J2EE with EJB and Weblogic interview questions

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					J2EE with EJB and Weblogic interview questions



1. What is the difference between URL instance and URLConnection instance?
   - A URL instance represents the location of a resource, and a URLConnection
   instance represents a link for accessing or communicating with the resource at the
   location.
2. What are the two important TCP Socket classes? - Socket and ServerSocket.
   ServerSocket is used for normal two-way socket communication. Socket class
   allows us to read and write through the sockets. getInputStream() and
   getOutputStream() are the two methods available in Socket class.
3. What technologies are included in J2EE? - The primary technologies in J2EE
   are: Enterprise JavaBeansTM (EJBsTM), JavaServer PagesTM (JSPsTM), Java
   Servlets, the Java Naming and Directory InterfaceTM (JNDITM), the Java
   Transaction API (JTA), CORBA, and the JDBCTM data access API.
4. What is the Java Authentication and Authorization Service (JAAS) 1.0? -
   The Java Authentication and Authorization Service (JAAS) provides a way for a
   J2EE application to authenticate and authorize a specific user or group of users to
   run it. JAAS is a Java programing language version of the standard Pluggable
   Authentication Module (PAM) framework that extends the Java 2 platform
   security architecture to support user-based authorization.
5. What‟s the difference between JNDI lookup(), list(), listBindings(), and
   search()? - lookup() attempts to find the specified object in the given context. I.e.,
   it looks for a single, specific object and either finds it in the current context or it
   fails. list() attempts to return an enumeration of all of the NameClassPair‟s of all
   of the objects in the current context. I.e., it‟s a listing of all of the objects in the
   current context but only returns the object‟s name and the name of the class to
   which the object belongs. listBindings() attempts to return an enumeration of the
   Binding‟s of all of the objects in the current context. I.e., it‟s a listing of all of the
   objects in the current context with the object‟s name, its class name, and a
   reference to the object itself. search() attempts to return an enumeration of all of
   the objects matching a given set of search criteria. It can search across multiple
   contexts (or not). It can return whatever attributes of the objects that you desire.
   It‟s by far the most complex and powerful of these options but is also the most
   expensive.
6. Components of JNDI - Naming Interface- The naming interface organizes
   information hierarchically and maps human-friendly names to addresses or
   objects that are machine-friendly. It allows access to named objects through
   multiple namespaces. Directory Interface - JNDI includes a directory service
   interface that provides access to directory objects, which can contain attributes,
   thereby providing attribute-based searching and schema support. Service Provider
   Interface - JNDI comes with the SPI, which supports the protocols provided by
   third parties.
7. What is the Max amount of information that can be saved in a Session
   Object? - As such there is no limit on the amount of information that can be



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    saved in a Session Object. Only the RAM available on the server machine is the
    limitation. The only limit is the Session ID length(Identifier), which should not
    exceed more than 4K. If the data to be store is very huge, then it‟s preferred to
    save it to a temporary file onto hard disk, rather than saving it in session.
    Internally if the amount of data being saved in Session exceeds the predefined
    limit, most of the servers write it to a temporary cache on Hard disk.
8. Must my bean-managed persistence mechanism use the WebLogic JTS
    driver? - BEA recommend that you use the TxDataSource for bean-managed
    persistence.
9. Do EJBs have to be homogeneously deployed across a cluster? Why? - Yes.
    Beginning with WebLogic Server version 6.0, EJBs must be homogeneously
    deployed across a cluster for the following reasons:
        o To keep clustering EJBs simple
        o To avoid cross server calls which results in more efficiency. If EJBs are
             not deployed on all servers, cross server calls are much more likely.
        o To ensure that every EJB is available locally
        o To ensure that all classes are loaded in an undeployable way
        o Every server must have access to each EJB‟s classes so that it can be
             bound into the local JNDI tree. If only a subset of the servers deploys the
             bean, the other servers will have to load the bean‟s classes in their
             respective system classpaths which makes it impossible to undeploy the
             beans.
10. Is an XSLT processor bundled in WebLogic Server? - Yes, an XSLT
    processor, based on Apache‟s Xalan 2.0.1 processor, in WebLogic Server 6.1.
11. I plugged in a version of Apache Xalan that I downloaded from the Apache
    Web site, and now I get errors when I try to transform documents. What is
    the problem? - You must ensure that the version of Apache Xalan you download
    from the Apache Web site is compatible with Apache Xerces version 1.3.1.
    Because you cannot plug in a different version of Apache Xerces , the only
    version of Apache Xerces that is compatible with WebLogic Server 6.1 is 1.3.1.
    The built-in parser (based on version 1.3.1 of Apache Xerces) and transformer
    (based on version 2.0.1 of Apache Xalan) have been modified by BEA to be
    compatible with each other.
12. How do I increase WebLogic Server memory? - Increase the allocation of Java
    heap memory for WebLogic Server. (Set the minimum and the maximum to the
    same size.) Start WebLogic Server with the -ms32m option to increase the
    allocation, as in this example:
13.             $ java ... -ms32m -mx32m ...

      This allocates 32 megabytes of Java heap memory to WebLogic Server, which
      improves performance and allows WebLogic Server to handle more simultaneous
      connections. You can increase this value if necessary.

14. What causes Java.io exceptions in the log file of WebLogic Server? - You may
    see messages like these in the log file:
15. (Windows NT)
16.         java.io.IOException Connection Reset by Peer



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17.         java.io.EOFException Connection Reset by Peer
18. (Solaris)
19.         java.io.Exception: Broken pipe

   These messages occur when you are using servlets. A client initiates an HTTP
   request, and then performs a series of actions on the browser:

       o   Click Stop or enter equivalent command or keystrokes
       o   Click Refresh or enter equivalent command or keystrokes
       o   Send a new HTTP request.

   The messages indicate that WebLogic Server has detected and recovered from an
   interrupted HTTP request.

20. What is the function of T3 in WebLogic Server? - T3 provides a framework for
    WebLogic Server messages that support for enhancements. These enhancements
    include abbreviations and features, such as object replacement, that work in the
    context of WebLogic Server clusters and HTTP and other product tunneling. T3
    predates Java Object Serialization and RMI, while closely tracking and leveraging
    these specifications. T3 is a superset of Java Object. Serialization or RMI;
    anything you can do in Java Object Serialization and RMI can be done over T3.
    T3 is mandated between WebLogic Servers and between programmatic clients
    and a WebLogic Server cluster. HTTP and IIOP are optional protocols that can be
    used to communicate between other processes and WebLogic Server. It depends
    on what you want to do. For example, when you want to communicate between a
    browser and WebLogic Server-use HTTP, or an ORB and WebLogic Server-
    IIOP.
21. What are the enhancements in EJB 2.0 specification with respect to
    Asynchronous communication? - EJB 2.0 mandates integration between JMS
    and EJB. We have specified the integration of Enterprise JavaBeans with the Java
    Message Service, and have introduced message-driven beans. A message-driven
    bean is a stateless component that is invoked by the container as a result of the
    arrival of a JMS message. The goal of the message-driven bean model is to make
    developing an enterprise bean that is asynchronously invoked to handle the
    processing of incoming JMS messages as simple as developing the same
    functionality in any other JMS MessageListener.
22. What are the enhancements in EJB 2.0 with respect to CMP? - EJB 2.0
    extends CMP to include far more robust modeling capability, with support for
    declarative management of relationships between entity EJBs. Developers no
    longer need to re-establish relationships between the various beans that make up
    their application – the container will restore the connections automatically as
    beans are loaded, allowing bean developers to navigate between beans much as
    they would between any standard Java objects.
    EJB 2.0 also introduces for the first time a portable query language, based on the
    abstract schema, not on the more complex database schema. This provides a
    database and vendor-independent way to find entity beans at run time, based on a
    wide variety of search criteria.


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23. Can you briefly describe local interfaces? - EJB was originally designed around
    remote invocation using the Java Remote Method Invocation (RMI) mechanism,
    and later extended to support to standard CORBA transport for these calls using
    RMI/IIOP. This design allowed for maximum flexibility in developing
    applications without consideration for the deployment scenario, and was a strong
    feature in support of a goal of component reuse in J2EE. Many developers are
    using EJBs locally - that is, some or all of their EJB calls are between beans in a
    single container. With this feedback in mind, the EJB 2.0 expert group has created
    a local interface mechanism. The local interface may be defined for a bean during
    development, to allow streamlined calls to the bean if a caller is in the same
    container. This does not involve the overhead involved with RMI like marshalling
    etc. This facility will thus improve the performance of applications in which co-
    location is planned. Local interfaces also provide the foundation for container-
    managed relationships among entity beans with container-managed persistence.
24. What are the special design care that must be taken when you work with
    local interfaces? - It is important to understand that the calling semantics of local
    interfaces are different from those of remote interfaces. For example, remote
    interfaces pass parameters using call-by-value semantics, while local interfaces
    use call-by-reference. This means that in order to use local interfaces safely,
    application developers need to carefully consider potential deployment scenarios
    up front, then decide which interfaces can be local and which remote, and finally,
    develop the application code with these choices in mind. While EJB 2.0 local
    interfaces are extremely useful in some situations, the long-term costs of these
    choices, especially when changing requirements and component reuse are taken
    into account, need to be factored into the design decision.
25. What happens if remove( ) is never invoked on a session bean? - In case of a
    stateless session bean it may not matter if we call or not as in both cases nothing
    is done. The number of beans in cache is managed by the container. In case of
    stateful session bean, the bean may be kept in cache till either the session times
    out, in which case the bean is removed or when there is a requirement for memory
    in which case the data is cached and the bean is sent to free pool.
26. What is the difference between creating a distributed application using RMI
    and using a EJB architecture? - It is possible to create the same application
    using RMI and EJB. But in case of EJB the container provides the requisite
    services to the component if we use the proper syntax. It thus helps in easier
    development and lesser error and use of proven code and methodology. But the
    investment on application server is mandatory in that case. But this investment is
    warranted because it results in less complex and maintainable code to the client,
    which is what the end client wants. Almost all the leading application servers
    provide load balancing and performance tuning techniques. In case of RMI we
    have to code the services and include in the program the way to invoke these
    services.
27. Why would a client application use JTA transactions? - One possible example
    would be a scenario in which a client needs to employ two (or more) session
    beans, where each session bean is deployed on a different EJB server and each
    bean performs operations against external resources (for example, a database)



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   and/or is managing one or more entity beans. In this scenario, the client‟s logic
   could required an all-or-nothing guarantee for the operations performed by the
   session beans; hence, the session bean usage could be bundled together with a
   JTA UserTransaction object. In the previous scenario, however, the client
   application developer should address the question of whether or not it would be
   better to encapsulate these operations in yet another session bean, and allow the
   session bean to handle the transactions via the EJB container. In general,
   lightweight clients are easier to maintain than heavyweight clients. Also, EJB
   environments are ideally suited for transaction management.
28. Context c = new InitialContext(); UserTransaction ut =
    (UserTransaction)
29. c.lookup("java:comp/UserTransaction");
30. ut.begin();
31.          // perform multiple operations...
32. ut.commit() ...
33. Can the bean class implement the EJBObject class directly? If not why? - It
    is better not to do it will make the Bean class a remote object and its methods can
    be accessed without the containers? security, and transaction implementations if
    our code by mistake passed it in one of its parameters. Its just a good design
    practice.
34. What does isIdentical() method return in case of different type of beans? -
    Stateless - true always. Stateful - depends whether the references point to the
    same session object. Entity - Depends whether the primary key is the same and
    the home is same.
35. How should you type cast a remote object? Why? - A client program that is
    intended to be interoperable with all compliant EJB Container implementations
    must use the javax.rmi.PortableRemoteObject.narrow(…) method to perform
    type-narrowing of the client-side representations of the remote home and remote
    interfaces. Programs using the cast operator for narrowing the remote and remote
    home interfaces are likely to fail if the Container implementation uses RMI-IIOP
    as the underlying communication transport.
36. What should you do in a passive method? - You try to make all nontransient
    variables, which are not one of the following to null. For the given list the
    container takes care of serializing and restoring the object when activated.
    Serializable objects, null, UserTransaction, SessionContext, JNDI contexts in the
    beans context, reference to other beans, references to connection pools.
    Things that must be handled explicitly are like a open database connection etc.
    These must be closed and set to null and retrieved back in the activate method.




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Interview questions for Java junior developer position

   1. What gives Java its “write once and run anywhere” nature? - Java is
       compiled to be a byte code which is the intermediate language between source
       code and machine code. This byte code is not platorm specific and hence can be
       fed to any platform. After being fed to the JVM, which is specific to a particular
       operating system, the code platform specific machine code is generated thus
       making java platform independent.
   2. What are the four corner stones of OOP? - Abstraction, Encapsulation,
       Polymorphism and Inheritance.
   3. Difference between a Class and an Object? - A class is a definition or prototype
       whereas an object is an instance or living representation of the prototype.
   4. What is the difference between method overriding and overloading? -
       Overriding is a method with the same name and arguments as in a parent, whereas
       overloading is the same method name but different arguments.
   5. What is a “stateless” protocol? - Without getting into lengthy debates, it is
       generally accepted that protocols like HTTP are stateless i.e. there is no retention
       of state between a transaction which is a single request response combination.
   6. What is constructor chaining and how is it achieved in Java? - A child object
       constructor always first needs to construct its parent (which in turn calls its parent
       constructor.). In Java it is done via an implicit call to the no-args constructor as
       the first statement.
   7. What is passed by ref and what by value? - All Java method arguments are
       passed by value. However, Java does manipulate objects by reference, and all
       object variables themselves are references
   8. Can RMI and Corba based applications interact? - Yes they can. RMI is
       available with IIOP as the transport protocol instead of JRMP.
   9. You can create a String object as String str = “abc"; Why cant a button
       object be created as Button bt = “abc";? Explain - The main reason you cannot
       create a button by Button bt1= “abc"; is because “abc” is a literal string
       (something slightly different than a String object, by the way) and bt1 is a Button
       object. The only object in Java that can be assigned a literal String is
       java.lang.String. Important to note that you are NOT calling a java.lang.String
       constuctor when you type String s = “abc";
   10. What does the “abstract” keyword mean in front of a method? A class? -
       Abstract keyword declares either a method or a class. If a method has a abstract
       keyword in front of it,it is called abstract method.Abstract method hs no body.It
       has only arguments and return type.Abstract methods act as placeholder methods
       that are implemented in the subclasses. Abstract classes can‟t be instantiated.If a
       class is declared as abstract,no objects of that class can be created.If a class
       contains any abstract method it must be declared as abstract.
   11. How many methods do u implement if implement the Serializable Interface?
       - The Serializable interface is just a “marker” interface, with no methods of its
       own to implement. Other „marker‟ interfaces are
   12.             java.rmi.Remote
   13.             java.util.EventListener




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14. What are the practical benefits, if any, of importing a specific class rather
    than an entire package (e.g. import java.net.* versus import
    java.net.Socket)? - It makes no difference in the generated class files since only
    the classes that are actually used are referenced by the generated class file. There
    is another practical benefit to importing single classes, and this arises when two
    (or more) packages have classes with the same name. Take java.util.Timer and
    javax.swing.Timer, for example. If I import java.util.* and javax.swing.* and then
    try to use “Timer", I get an error while compiling (the class name is ambiguous
    between both packages). Let‟s say what you really wanted was the
    javax.swing.Timer class, and the only classes you plan on using in java.util are
    Collection and HashMap. In this case, some people will prefer to import
    java.util.Collection and import java.util.HashMap instead of importing java.util.*.
    This will now allow them to use Timer, Collection, HashMap, and other
    javax.swing classes without using fully qualified class names in.
15. What is the difference between logical data independence and physical data
    independence? - Logical Data Independence - meaning immunity of external
    schemas to changeds in conceptual schema. Physical Data Independence -
    meaning immunity of conceptual schema to changes in the internal schema.
16. What is a user-defined exception? - Apart from the exceptions already defined
    in Java package libraries, user can define his own exception classes by extending
    Exception class.
17. Describe the visitor design pattern? - Represents an operation to be performed
    on the elements of an object structure. Visitor lets you define a new operation
    without changing the classes of the elements on which it operates. The root of a
    class hierarchy defines an abstract method to accept a visitor. Subclasses
    implement this method with visitor.visit(this). The Visitor interface has visit
    methods for all subclasses of the baseclass in the hierarchy.




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Java database interview questions

   1. How do you call a Stored Procedure from JDBC? - The first step is to create a
      CallableStatement object. As with Statement and PreparedStatement objects, this
      is done with an open Connection object. A CallableStatement object contains a
      call to a stored procedure.
   2.             CallableStatement cs =
   3.                     con.prepareCall("{call SHOW_SUPPLIERS}");
   4.             ResultSet rs = cs.executeQuery();
   5. Is the JDBC-ODBC Bridge multi-threaded? - No. The JDBC-ODBC Bridge
       does not support concurrent access from different threads. The JDBC-ODBC
       Bridge uses synchronized methods to serialize all of the calls that it makes to
       ODBC. Multi-threaded Java programs may use the Bridge, but they won‟t get the
       advantages of multi-threading.
   6. Does the JDBC-ODBC Bridge support multiple concurrent open statements
       per connection? - No. You can open only one Statement object per connection
       when you are using the JDBC-ODBC Bridge.
   7. What is cold backup, hot backup, warm backup recovery? - Cold backup (All
       these files must be backed up at the same time, before the databaseis restarted).
       Hot backup (official name is „online backup‟) is a backup taken of each
       tablespace while the database is running and is being accessed by the users.
   8. When we will Denormalize data? - Data denormalization is reverse procedure,
       carried out purely for reasons of improving performance. It maybe efficient for a
       high-throughput system to replicate data for certain data.
   9. What is the advantage of using PreparedStatement? - If we are using
       PreparedStatement the execution time will be less. The PreparedStatement object
       contains not just an SQL statement, but the SQL statement that has been
       precompiled. This means that when the PreparedStatement is executed,the
       RDBMS can just run the PreparedStatement‟s Sql statement without having to
       compile it first.
   10. What is a “dirty read"? - Quite often in database processing, we come across
       the situation wherein one transaction can change a value, and a second transaction
       can read this value before the original change has been committed or rolled back.
       This is known as a dirty read scenario because there is always the possibility that
       the first transaction may rollback the change, resulting in the second transaction
       having read an invalid value. While you can easily command a database to
       disallow dirty reads, this usually degrades the performance of your application
       due to the increased locking overhead. Disallowing dirty reads also leads to
       decreased system concurrency.
   11. What is Metadata and why should I use it? - Metadata (‟data about data‟) is
       information about one of two things: Database information
       (java.sql.DatabaseMetaData), or Information about a specific ResultSet
       (java.sql.ResultSetMetaData). Use DatabaseMetaData to find information about
       your database, such as its capabilities and structure. Use ResultSetMetaData to
       find information about the results of an SQL query, such as size and types of
       columns



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   12. Different types of Transaction Isolation Levels? - The isolation level describes
       the degree to which the data being updated is visible to other transactions. This is
       important when two transactions are trying to read the same row of a table.
       Imagine two transactions: A and B. Here three types of inconsistencies can occur:
           o Dirty-read: A has changed a row, but has not committed the changes. B
              reads the uncommitted data but his view of the data may be wrong if A
              rolls back his changes and updates his own changes to the database.
           o Non-repeatable read: B performs a read, but A modifies or deletes that
              data later. If B reads the same row again, he will get different data.
           o Phantoms: A does a query on a set of rows to perform an operation. B
              modifies the table such that a query of A would have given a different
              result. The table may be inconsistent.

       TRANSACTION_READ_UNCOMMITTED : DIRTY READS, NON-
       REPEATABLE READ AND PHANTOMS CAN OCCUR.
       TRANSACTION_READ_COMMITTED : DIRTY READS ARE PREVENTED,
       NON-REPEATABLE READ AND PHANTOMS CAN OCCUR.
       TRANSACTION_REPEATABLE_READ : DIRTY READS , NON-
       REPEATABLE READ ARE PREVENTED AND PHANTOMS CAN OCCUR.
       TRANSACTION_SERIALIZABLE : DIRTY READS, NON-REPEATABLE
       READ AND PHANTOMS ARE PREVENTED.

   13. What is 2 phase commit? - A 2-phase commit is an algorithm used to ensure the
       integrity of a committing transaction. In Phase 1, the transaction coordinator
       contacts potential participants in the transaction. The participants all agree to
       make the results of the transaction permanent but do not do so immediately. The
       participants log information to disk to ensure they can complete In phase 2 f all
       the participants agree to commit, the coordinator logs that agreement and the
       outcome is decided. The recording of this agreement in the log ends in Phase 2,
       the coordinator informs each participant of the decision, and they permanently
       update their resources.
   14. How do you handle your own transaction ? - Connection Object has a method
       called setAutocommit(Boolean istrue)
       - Default is true. Set the Parameter to false , and begin your transaction
   15. What is the normal procedure followed by a java client to access the db.? -
       The database connection is created in 3 steps:
           1. Find a proper database URL
2.     Load the database driver
           3. Ask the Java DriverManager class to open a connection to your database

       In java code, the steps are realized in code as follows:

4.     Create a properly formatted JDBR URL for your database. (See FAQ on JDBC
URL for more information). A JDBC URL has the form
jdbc:someSubProtocol://myDatabaseServer/theDatabaseName
5.     Class.forName("my.database.driver");



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          6. Connection conn = DriverManager.getConnection("a.JDBC.URL",
              “databaseLogin","databasePassword");
  16. What is a data source? - A DataSource class brings another level of abstraction
      than directly using a connection object. Data source can be referenced by JNDI.
      Data Source may point to RDBMS, file System , any DBMS etc.
  17. What are collection pools? What are the advantages? - A connection pool is a
      cache of database connections that is maintained in memory, so that the
      connections may be reused
  18. How do you get Column names only for a table (SQL Server)? Write the
      Query. -
  19.          select name from syscolumns
  20.                  where id=(select id from sysobjects where
      name='user_hdr')
  21.                  order by colid --user_hdr is the table name

Java Messaging System interview questions

  1. What are the types of messaging? - There are two kinds of Messaging.
     Synchronous messaging involves a client that waits for the server to respond to a
     message. Asynchronous messaging involves a client that does not wait for a
     message from the server. An event is used to trigger a message from a server.
  2. What is publish/subscribe messaging? - With publish/subscribe message
     passing the sending application/client establishes a named topic in the JMS
     broker/server and publishes messages to this queue. The receiving clients register
     (specifically, subscribe) via the broker to messages by topic; every subscriber to a
     topic receives each message published to that topic. There is a one-to-many
     relationship between the publishing client and the subscribing clients.
  3. Why doesn‟t the JMS API provide end-to-end synchronous message delivery
     and notification of delivery? -Some messaging systems provide synchronous
     delivery to destinations as a mechanism for implementing reliable applications.
     Some systems provide clients with various forms of delivery notification so that
     the clients can detect dropped or ignored messages. This is not the model defined
     by the JMS API. JMS API messaging provides guaranteed delivery via the once-
     and-only-once delivery semantics of PERSISTENT messages. In addition,
     message consumers can insure reliable processing of messages by using either
     CLIENT_ACKNOWLEDGE mode or transacted sessions. This achieves reliable
     delivery with minimum synchronization and is the enterprise messaging model
     most vendors and developers prefer. The JMS API does not define a schema of
     systems messages (such as delivery notifications). If an application requires
     acknowledgment of message receipt, it can define an application-level
     acknowledgment message.
  4. What are the core JMS-related objects required for each JMS-enabled
     application? - Each JMS-enabled client must establish the following:
         o A connection object provided by the JMS server (the message broker)
         o Within a connection, one or more sessions, which provide a context for
             message sending and receiving



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             o     Within a session, either a queue or topic object representing the
                   destination (the message staging area) within the message broker
              o Within a session, the appropriate sender or publisher or receiver or
                   subscriber object (depending on whether the client is a message producer
                   or consumer and uses a point-to-point or publish/subscribe strategy,
                   respectively). Within a session, a message object (to send or to receive)
     5.   What is the Role of the JMS Provider? - The JMS provider handles security of
          the messages, data conversion and the client triggering. The JMS provider
          specifies the level of encryption and the security level of the message, the best
          data type for the non-JMS client.
     6.   How does a typical client perform the communication? -
              1. Use JNDI to locate administrative objects.
2.        Locate a single ConnectionFactory object.
              3. Locate one or more Destination objects.
              4. Use the ConnectionFactory to create a JMS Connection.
              5. Use the Connection to create one or more Session(s).
              6. Use a Session and the Destinations to create the MessageProducers and
                   MessageConsumers needed.
              7. Perform your communication.
     7.   Give an example of using the point-to-point model. - The point-to-point model
          is used when the information is specific to a single client. For example, a client
          can send a message for a print out, and the server can send information back to
          this client after completion of the print job.
     8.   How does the Application server handle the JMS Connection? -
              0. App server creates the server session and stores them in a pool.
1.        Connection consumer uses the server session to put messages in the session of the
JMS.
             2. Server session is the one that spawns the JMS session.
             3. Applications written by Application programmers creates the message
                listener.

Common JSP interview questions

     1. What are the implicit objects? - Implicit objects are objects that are created by
        the web container and contain information related to a particular request, page, or
        application. They are: request, response, pageContext, session, application, out,
        config, page, exception.
     2. Is JSP technology extensible? - Yes. JSP technology is extensible through the
        development of custom actions, or tags, which are encapsulated in tag libraries.
     3. How can I implement a thread-safe JSP page? What are the advantages and
        Disadvantages of using it? - You can make your JSPs thread-safe by having
        them implement the SingleThreadModel interface. This is done by adding the
        directive <%@ page isThreadSafe="false" %> within your JSP page. With this,
        instead of a single instance of the servlet generated for your JSP page loaded in
        memory, you will have N instances of the servlet loaded and initialized, with the
        service method of each instance effectively synchronized. You can typically


                                                                                         11
   control the number of instances (N) that are instantiated for all servlets
   implementing SingleThreadModel through the admin screen for your JSP engine.
   More importantly, avoid using the tag for variables. If you do use this tag, then
   you should set isThreadSafe to true, as mentioned above. Otherwise, all requests
   to that page will access those variables, causing a nasty race condition.
   SingleThreadModel is not recommended for normal use. There are many pitfalls,
   including the example above of not being able to use <%! %>. You should try
   really hard to make them thread-safe the old fashioned way: by making them
   thread-safe
4. How does JSP handle run-time exceptions? - You can use the errorPage
   attribute of the page directive to have uncaught run-time exceptions automatically
   forwarded to an error processing page. For example: <%@ page
   errorPage="error.jsp" %>
   redirects the browser to the JSP page error.jsp if an uncaught exception is
   encountered during request processing. Within error.jsp, if you indicate that it is
   an error-processing page, via the directive: <%@ page isErrorPage="true" %>
   Throwable object describing the exception may be accessed within the error page
   via the exception implicit object. Note: You must always use a relative URL as
   the value for the errorPage attribute.
5. How do I prevent the output of my JSP or Servlet pages from being cached
   by the browser? - You will need to set the appropriate HTTP header attributes to
   prevent the dynamic content output by the JSP page from being cached by the
   browser. Just execute the following scriptlet at the beginning of your JSP pages to
   prevent them from being cached at the browser. You need both the statements to
   take care of some of the older browser versions.

      <%
      response.setHeader("Cache-Control","no-store"); //HTTP 1.1
      response.setHeader("Pragma","no-cache"); //HTTP 1.0
      response.setDateHeader ("Expires", 0); //prevents caching at the proxy server
      %>

6. How do I use comments within a JSP page? - You can use “JSP-style”
   comments to selectively block out code while debugging or simply to comment
   your scriptlets. JSP comments are not visible at the client. For example:
7.               <%-- the scriptlet is now commented out
8.               <%
9.               out.println("Hello World");
10.              %>
11.              --%>

      You can also use HTML-style comments anywhere within your JSP page. These
      comments are visible at the client. For example:

      <!-- (c) 2004 -->




                                                                                      12
   Of course, you can also use comments supported by your JSP scripting language
   within your scriptlets. For example, assuming Java is the scripting language, you
   can have:

      <%
      //some comment
      /**
      yet another comment
      **/
      %>

12. Response has already been commited error. What does it mean? - This error
    show only when you try to redirect a page after you already have written
    something in your page. This happens because HTTP specification force the
    header to be set up before the lay out of the page can be shown (to make sure of
    how it should be displayed, content-type="text/html” or “text/xml” or “plain-text”
    or “image/jpg", etc.) When you try to send a redirect status (Number is
    line_status_402), your HTTP server cannot send it right now if it hasn‟t finished
    to set up the header. If not starter to set up the header, there are no problems, but
    if it ‟s already begin to set up the header, then your HTTP server expects these
    headers to be finished setting up and it cannot be the case if the stream of the page
    is not over… In this last case it‟s like you have a file started with <HTML
    Tag><Some Headers><Body>some output (like testing your variables.) Before
    you indicate that the file is over (and before the size of the page can be setted up
    in the header), you try to send a redirect status. It s simply impossible due to the
    specification of HTTP 1.0 and 1.1
13. How do I use a scriptlet to initialize a newly instantiated bean? - A
    jsp:useBean action may optionally have a body. If the body is specified, its
    contents will be automatically invoked when the specified bean is instantiated.
    Typically, the body will contain scriptlets or jsp:setProperty tags to initialize the
    newly instantiated bean, although you are not restricted to using those alone.
    The following example shows the “today” property of the Foo bean initialized to
    the current date when it is instantiated. Note that here, we make use of a JSP
    expression within the jsp:setProperty action.
14. <jsp:useBean id="foo" class="com.Bar.Foo" >
15. <jsp:setProperty name="foo" property="today"
16. value="<%=java.text.DateFormat.getDateInstance().format(new
   java.util.Date()) %>"/ >
17. <%-- scriptlets calling bean setter methods go here --%>
18. </jsp:useBean >
19. How can I enable session tracking for JSP pages if the browser has disabled
    cookies? - We know that session tracking uses cookies by default to associate a
    session identifier with a unique user. If the browser does not support cookies, or if
    cookies are disabled, you can still enable session tracking using URL rewriting.
    URL rewriting essentially includes the session ID within the link itself as a
    name/value pair. However, for this to be effective, you need to append the session
    ID for each and every link that is part of your servlet response. Adding the session
    ID to a link is greatly simplified by means of of a couple of methods:
    response.encodeURL() associates a session ID with a given URL, and if you are


                                                                                      13
      using redirection, response.encodeRedirectURL() can be used by giving the
      redirected URL as input. Both encodeURL() and encodeRedirectedURL() first
      determine whether cookies are supported by the browser; if so, the input URL is
      returned unchanged since the session ID will be persisted as a cookie. Consider
      the following example, in which two JSP files, say hello1.jsp and hello2.jsp,
      interact with each other. Basically, we create a new session within hello1.jsp and
      place an object within this session. The user can then traverse to hello2.jsp by
      clicking on the link present within the page.Within hello2.jsp, we simply extract
      the object that was earlier placed in the session and display its contents. Notice
      that we invoke the encodeURL() within hello1.jsp on the link used to invoke
      hello2.jsp; if cookies are disabled, the session ID is automatically appended to the
      URL, allowing hello2.jsp to still retrieve the session object. Try this example first
      with cookies enabled. Then disable cookie support, restart the brower, and try
      again. Each time you should see the maintenance of the session across pages. Do
      note that to get this example to work with cookies disabled at the browser, your
      JSP engine has to support URL rewriting.
20.               hello1.jsp
21.               <%@ page session="true" %>
22.               <%
23.               Integer num = new Integer(100);
24.               session.putValue("num",num);
25.               String url =response.encodeURL("hello2.jsp");
26.               %>
27.               <a href='<%=url%>'>hello2.jsp</a>
28.               hello2.jsp
29.               <%@ page session="true" %>
30.               <%
31.               Integer i= (Integer )session.getValue("num");
32.               out.println("Num value in session is "+i.intValue());
33. How can I declare methods within my JSP page? - You can declare methods
    for use within your JSP page as declarations. The methods can then be invoked
    within any other methods you declare, or within JSP scriptlets and expressions.
    Do note that you do not have direct access to any of the JSP implicit objects like
    request, response, session and so forth from within JSP methods. However, you
    should be able to pass any of the implicit JSP variables as parameters to the
    methods you declare. For example:
34.               <%!
35.               public String whereFrom(HttpServletRequest req) {
36.               HttpSession ses = req.getSession();
37.               ...
38.               return req.getRemoteHost();
39.               }
40.               %>
41.               <%
42.               out.print("Hi there, I see that you are coming in from
      ");
43.               %>
44.               <%= whereFrom(request) %>
45.               Another Example
46.               file1.jsp:
47.               <%@page contentType="text/html"%>
48.               <%!


                                                                                         14
49.               public void test(JspWriter writer) throws IOException{
50.               writer.println("Hello!");
51.               }
52.               %>
53.               file2.jsp
54.               <%@include file="file1.jsp"%>
55.               <html>
56.               <body>
57.               <%test(out);% >
58.               </body>
59.               </html>
60. Is there a way I can set the inactivity lease period on a per-session basis? -
    Typically, a default inactivity lease period for all sessions is set within your JSP
    engine admin screen or associated properties file. However, if your JSP engine
    supports the Servlet 2.1 API, you can manage the inactivity lease period on a per-
    session basis. This is done by invoking the HttpSession.setMaxInactiveInterval()
    method, right after the session has been created. For example:
61.               <%
62.               session.setMaxInactiveInterval(300);
63.               %>

      would reset the inactivity period for this session to 5 minutes. The inactivity
      interval is set in seconds.

64. How can I set a cookie and delete a cookie from within a JSP page? - A
    cookie, mycookie, can be deleted using the following scriptlet:
65.               <%
66.               //creating a cookie
67.               Cookie mycookie = new Cookie("aName","aValue");
68.               response.addCookie(mycookie);
69.               //delete a cookie
70.               Cookie killMyCookie = new Cookie("mycookie", null);
71.               killMyCookie.setMaxAge(0);
72.               killMyCookie.setPath("/");
73.               response.addCookie(killMyCookie);
74.               %>
75. How does a servlet communicate with a JSP page? - The following code
    snippet shows how a servlet instantiates a bean and initializes it with FORM data
    posted by a browser. The bean is then placed into the request, and the call is then
    forwarded to the JSP page, Bean1.jsp, by means of a request dispatcher for
    downstream processing.
76.          public void doPost (HttpServletRequest request,
    HttpServletResponse response) {
77.          try {
78.                  govi.FormBean f = new govi.FormBean();
79.                  String id = request.getParameter("id");
80.                  f.setName(request.getParameter("name"));
81.                  f.setAddr(request.getParameter("addr"));
82.                  f.setAge(request.getParameter("age"));
83.                  //use the id to compute
84.                  //additional bean properties like info
85.                  //maybe perform a db query, etc.
86.                  // . . .



                                                                                        15
87.                        f.setPersonalizationInfo(info);
88.                        request.setAttribute("fBean",f);
89.
      getServletConfig().getServletContext().getRequestDispatcher
90.                         ("/jsp/Bean1.jsp").forward(request,
    response);
91.                  } catch (Exception ex) {
92.           . . .
93.              }
94.           }

      The JSP page Bean1.jsp can then process fBean, after first extracting it from the
      default request scope via the useBean action.

      jsp:useBean id="fBean" class="govi.FormBean" scope="request"
      / jsp:getProperty name="fBean" property="name"
      / jsp:getProperty name="fBean" property="addr"
      / jsp:getProperty name="fBean" property="age"
      / jsp:getProperty name="fBean" property="personalizationInfo" /

95. How do I have the JSP-generated servlet subclass my own custom servlet
    class, instead of the default? - One should be very careful when having JSP
    pages extend custom servlet classes as opposed to the default one generated by
    the JSP engine. In doing so, you may lose out on any advanced optimization that
    may be provided by the JSP engine. In any case, your new superclass has to fulfill
    the contract with the JSP engine by:
    Implementing the HttpJspPage interface, if the protocol used is HTTP, or
    implementing JspPage otherwise Ensuring that all the methods in the Servlet
    interface are declared final Additionally, your servlet superclass also needs to do
    the following:
        o The service() method has to invoke the _jspService() method
        o The init() method has to invoke the jspInit() method
        o The destroy() method has to invoke jspDestroy()

      If any of the above conditions are not satisfied, the JSP engine may throw a
      translation error.
      Once the superclass has been developed, you can have your JSP extend it as
      follows:

        <%@ page extends="packageName.ServletName" %>

96. How can I prevent the word "null" from appearing in my HTML input text
    fields when I populate them with a resultset that has null values? - You could
    make a simple wrapper function, like
97.              <%!
98.              String blanknull(String s) {
99.              return (s == null) ? "" : s;
100.             }
101.             %>
102.             then use it inside your JSP form, like



                                                                                      16
103.        <input type="text" name="shoesize"
   value="<%=blanknull(shoesize)% >" >
104.       How can I get to print the stacktrace for an exception occuring within
   my JSP page? - By printing out the exception‟s stack trace, you can usually
   diagonse a problem better when debugging JSP pages. By looking at a stack trace,
   a programmer should be able to discern which method threw the exception and
   which method called that method. However, you cannot print the stacktrace using
   the JSP out implicit variable, which is of type JspWriter. You will have to use a
   PrintWriter object instead. The following snippet demonstrates how you can print
   a stacktrace from within a JSP error page:
105.           <%@ page isErrorPage="true" %>
106.           <%
107.           out.println(" ");
108.            PrintWriter pw = response.getWriter();
109.            exception.printStackTrace(pw);
110.           out.println(" ");
111.           %>
112.       How do you pass an InitParameter to a JSP? - The JspPage interface
   defines the jspInit() and jspDestroy() method which the page writer can use in
   their pages and are invoked in much the same manner as the init() and destory()
   methods of a servlet. The example page below enumerates through all the
   parameters and prints them to the console.
113.        <%@ page import="java.util.*" %>
114.        <%!
115.        ServletConfig cfg =null;
116.        public void jspInit(){
117.        ServletConfig cfg=getServletConfig();
118.        for (Enumeration e=cfg.getInitParameterNames();
   e.hasMoreElements();) {
119.        String name=(String)e.nextElement();
120.        String value = cfg.getInitParameter(name);
121.        System.out.println(name+"="+value);
122.        }
123.        }
124.        %>
125.      How can my JSP page communicate with an EJB Session Bean? - The
   following is a code snippet that demonstrates how a JSP page can interact with an
   EJB session bean:
126.        <%@ page import="javax.naming.*,
   javax.rmi.PortableRemoteObject, foo.AccountHome, foo.Account" %>
127.        <%!
128.        //declare a "global" reference to an instance of the
   home interface of the session bean
129.        AccountHome accHome=null;
130.        public void jspInit() {
131.        //obtain an instance of the home interface
132.        InitialContext cntxt = new InitialContext( );
133.        Object ref=
   cntxt.lookup("java:comp/env/ejb/AccountEJB");
134.        accHome =
   (AccountHome)PortableRemoteObject.narrow(ref,AccountHome.class);
135.        }
136.        %>



                                                                                     17
   137.           <%
   138.           //instantiate the session bean
   139.           Account acct = accHome.create();
   140.           //invoke the remote methods
   141.           acct.doWhatever(...);
   142.           // etc etc...
   143.           %>




Java interview questions

   1. What is the Collections API? - The Collections API is a set of classes and
       interfaces that support operations on collections of objects
   2. What is the List interface? - The List interface provides support for ordered
       collections of objects.
   3. What is the Vector class? - The Vector class provides the capability to
       implement a growable array of objects
   4. What is an Iterator interface? - The Iterator interface is used to step through the
       elements of a Collection
   5. Which java.util classes and interfaces support event handling? - The
       EventObject class and the EventListener interface support event processing
   6. What is the GregorianCalendar class? - The GregorianCalendar provides
       support for traditional Western calendars
   7. What is the Locale class? - The Locale class is used to tailor program output to
       the conventions of a particular geographic, political, or cultural region
   8. What is the SimpleTimeZone class? - The SimpleTimeZone class provides
       support for a Gregorian calendar
   9. What is the Map interface? - The Map interface replaces the JDK 1.1 Dictionary
       class and is used associate keys with values
   10. What is the highest-level event class of the event-delegation model? - The
       java.util.EventObject class is the highest-level class in the event-delegation class
       hierarchy
   11. What is the Collection interface? - The Collection interface provides support for
       the implementation of a mathematical bag - an unordered collection of objects
       that may contain duplicates
   12. What is the Set interface? - The Set interface provides methods for accessing the
       elements of a finite mathematical set. Sets do not allow duplicate elements
   13. What is the purpose of the enableEvents() method? - The enableEvents()
       method is used to enable an event for a particular object. Normally, an event is
       enabled when a listener is added to an object for a particular event. The
       enableEvents() method is used by objects that handle events by overriding their
       event-dispatch methods.
   14. What is the ResourceBundle class? - The ResourceBundle class is used to store
       locale-specific resources that can be loaded by a program to tailor the program‟s
       appearance to the particular locale in which it is being run.




                                                                                        18
15. What is the difference between yielding and sleeping? - When a task invokes
    its yield() method, it returns to the ready state. When a task invokes its sleep()
    method, it returns to the waiting state.
16. When a thread blocks on I/O, what state does it enter? - A thread enters the
    waiting state when it blocks on I/O.
17. When a thread is created and started, what is its initial state? - A thread is in
    the ready state after it has been created and started.
18. What invokes a thread‟s run() method? - After a thread is started, via its start()
    method or that of the Thread class, the JVM invokes the thread‟s run() method
    when the thread is initially executed.
19. What method is invoked to cause an object to begin executing as a separate
    thread? - The start() method of the Thread class is invoked to cause an object to
    begin executing as a separate thread.
20. What is the purpose of the wait(), notify(), and notifyAll() methods? - The
    wait(),notify(), and notifyAll() methods are used to provide an efficient way for
    threads to wait for a shared resource. When a thread executes an object‟s wait()
    method, it enters the waiting state. It only enters the ready state after another
    thread invokes the object‟s notify() or notifyAll() methods.
21. What are the high-level thread states? - The high-level thread states are ready,
    running, waiting, and dead
22. What happens when a thread cannot acquire a lock on an object? - If a thread
    attempts to execute a synchronized method or synchronized statement and is
    unable to acquire an object‟s lock, it enters the waiting state until the lock
    becomes available.
23. How does multithreading take place on a computer with a single CPU? - The
    operating system‟s task scheduler allocates execution time to multiple tasks. By
    quickly switching between executing tasks, it creates the impression that tasks
    execute sequentially.
24. What happens when you invoke a thread‟s interrupt method while it is
    sleeping or waiting? - When a task‟s interrupt() method is executed, the task
    enters the ready state. The next time the task enters the running state, an
    InterruptedException is thrown.
25. What state is a thread in when it is executing? - An executing thread is in the
    running state
26. What are three ways in which a thread can enter the waiting state? - A thread
    can enter the waiting state by invoking its sleep() method, by blocking on I/O, by
    unsuccessfully attempting to acquire an object‟s lock, or by invoking an object‟s
    wait() method. It can also enter the waiting state by invoking its (deprecated)
    suspend() method.
27. What method must be implemented by all threads? - All tasks must implement
    the run() method, whether they are a subclass of Thread or implement the
    Runnable interface.
28. What are the two basic ways in which classes that can be run as threads may
    be defined? - A thread class may be declared as a subclass of Thread, or it may
    implement the Runnable interface.




                                                                                   19
   29. How can you store international / Unicode characters into a cookie? - One
       way is, before storing the cookie URLEncode it. URLEnocder.encoder(str); And
       use URLDecoder.decode(str) when you get the stored cookie.

Java GUI designer interview questions

   1. What advantage do Java‟s layout managers provide over traditional
      windowing systems? - Java uses layout managers to lay out components in a
      consistent manner across all windowing platforms. Since Java‟s layout managers
      aren‟t tied to absolute sizing and positioning, they are able to accomodate
      platform-specific differences among windowing systems.
   2. What is the difference between the paint() and repaint() methods? - The
      paint() method supports painting via a Graphics object. The repaint() method is
      used to cause paint() to be invoked by the AWT painting thread.
   3. How can the Checkbox class be used to create a radio button? - By
      associating Checkbox objects with a CheckboxGroup
   4. What is the difference between a Choice and a List? - A Choice is displayed in
      a compact form that requires you to pull it down to see the list of available
      choices. Only one item may be selected from a Choice. A List may be displayed
      in such a way that several List items are visible. A List supports the selection of
      one or more List items.
   5. What interface is extended by AWT event listeners? - All AWT event listeners
      extend the java.util.EventListener interface.
   6. What is a layout manager? - A layout manager is an object that is used to
      organize components in a container
   7. Which Component subclass is used for drawing and painting? - Canvas
   8. What are the problems faced by Java programmers who dont use layout
      managers? - Without layout managers, Java programmers are faced with
      determining how their GUI will be displayed across multiple windowing systems
      and finding a common sizing and positioning that will work within the constraints
      imposed by each windowing system
   9. What is the difference between a Scrollbar and a ScrollPane? (Swing) - A
      Scrollbar is a Component, but not a Container. A ScrollPane is a Container.
      A ScrollPane handles its own events and performs its own scrolling.

J2EE interview questions

Thanks to Sachin Rastogi for contributing these.

   1. What makes J2EE suitable for distributed multitiered Applications?
      - The J2EE platform uses a multitiered distributed application model. Application
      logic is divided into components according to function, and the various
      application components that make up a J2EE application are installed on different
      machines depending on the tier in the multitiered J2EE environment to which the
      application component belongs. The J2EE application parts are:
          o Client-tier components run on the client machine.



                                                                                      20
             o     Web-tier components run on the J2EE server.
             o     Business-tier components run on the J2EE server.
             o     Enterprise information system (EIS)-tier software runs on the EIS server.
     2.   What is J2EE? - J2EE is an environment for developing and deploying enterprise
          applications. The J2EE platform consists of a set of services, application
          programming interfaces (APIs), and protocols that provide the functionality for
          developing multitiered, web-based applications.
     3.   What are the components of J2EE application?
          - A J2EE component is a self-contained functional software unit that is assembled
          into a J2EE application with its related classes and files and communicates with
          other components. The J2EE specification defines the following J2EE
          components:
1.        Application clients and applets are client components.
              2. Java Servlet and JavaServer Pages technology components are web
                   components.
              3. Enterprise JavaBeans components (enterprise beans) are business
                   components.
              4. Resource adapter components provided by EIS and tool vendors.
     4.   What do Enterprise JavaBeans components contain? - Enterprise JavaBeans
          components contains Business code, which is logic
          that solves or meets the needs of a particular business domain such as banking,
          retail, or finance, is handled by enterprise beans running in the business tier. All
          the business code is contained inside an Enterprise Bean which receives data from
          client programs, processes it (if necessary), and sends it to the enterprise
          information system tier for storage. An enterprise bean also retrieves data from
          storage, processes it (if necessary), and sends it back to the client program.
     5.   Is J2EE application only a web-based? - No, It depends on type of application
          that client wants. A J2EE application can be web-based or non-web-based. if an
          application client executes on the client machine, it is a non-web-based J2EE
          application. The J2EE application can provide a way for users to handle tasks
          such as J2EE system or application administration. It typically has a graphical
          user interface created from Swing or AWT APIs, or a command-line interface.
          When user request, it can open an HTTP connection to establish communication
          with a servlet running in the web tier.
     6.   Are JavaBeans J2EE components? - No. JavaBeans components are not
          considered J2EE components by the J2EE specification. They are written to
          manage the data flow between an application client or applet and components
          running on the J2EE server or between server components and a database.
          JavaBeans components written for the J2EE platform have instance variables and
          get and set methods for accessing the data in the instance variables. JavaBeans
          components used in this way are typically simple in design and implementation,
          but should conform to the naming and design conventions outlined in the
          JavaBeans component architecture.
     7.   Is HTML page a web component? - No. Static HTML pages and applets are
          bundled with web components during application assembly, but are not




                                                                                           21
    considered web components by the J2EE specification. Even the server-side
    utility classes are not considered web components, either.
8. What can be considered as a web component? - J2EE Web components can be
    either servlets or JSP pages. Servlets are Java programming language classes that
    dynamically process requests and construct responses. JSP pages are text-based
    documents that execute as servlets but allow a more natural approach to creating
    static content.
9. What is the container? - Containers are the interface between a component and
    the low-level platform specific functionality that supports the component. Before
    a Web, enterprise bean, or application client component can be executed, it must
    be assembled into a J2EE application and deployed into its container.
10. What are container services? - A container is a runtime support of a system-
    level entity. Containers provide components with services such as lifecycle
    management, security, deployment, and threading.
11. What is the web container? - Servlet and JSP containers are collectively referred
    to as Web containers. It manages the execution of JSP page and servlet
    components for J2EE applications. Web components and their container run on
    the J2EE server.
12. What is Enterprise JavaBeans (EJB) container? - It manages the execution of
    enterprise beans for J2EE applications.
    Enterprise beans and their container run on the J2EE server.
13. What is Applet container? - IManages the execution of applets. Consists of a
    Web browser and Java Plugin running on the client together.
14. How do we package J2EE components? - J2EE components are packaged
    separately and bundled into a J2EE application for deployment. Each component,
    its related files such as GIF and HTML files or server-side utility classes, and a
    deployment descriptor are assembled into a module and added to the J2EE
    application. A J2EE application is composed of one or more enterprise bean,Web,
    or application client component modules. The final enterprise solution can use
    one J2EE application or be made up of two or more J2EE applications, depending
    on design requirements. A J2EE application and each of its modules has its own
    deployment descriptor. A deployment descriptor is an XML document with an
    .xml extension that describes a component‟s deployment settings.
15. What is a thin client? - A thin client is a lightweight interface to the application
    that does not have such operations like query databases, execute complex business
    rules, or connect to legacy applications.
16. What are types of J2EE clients? - Following are the types of J2EE clients:
         o Applets
         o Application clients
         o Java Web Start-enabled rich clients, powered by Java Web Start
             technology.
         o Wireless clients, based on Mobile Information Device Profile (MIDP)
             technology.
17. What is deployment descriptor? - A deployment descriptor is an Extensible
    Markup Language (XML) text-based file with an .xml extension that describes a
    component‟s deployment settings. A J2EE application and each of its modules has



                                                                                     22
    its own deployment descriptor. For example, an enterprise bean module
    deployment descriptor declares transaction attributes and security authorizations
    for an enterprise bean. Because deployment descriptor information is declarative,
    it can be changed without modifying the bean source code. At run time, the J2EE
    server reads the deployment descriptor and acts upon the component accordingly.
18. What is the EAR file? - An EAR file is a standard JAR file with an .ear
    extension, named from Enterprise ARchive file. A J2EE application with all of its
    modules is delivered in EAR file.
19. What is JTA and JTS? - JTA is the abbreviation for the Java Transaction API.
    JTS is the abbreviation for the Jave Transaction Service. JTA provides a standard
    interface and allows you to demarcate transactions in a manner that is independent
    of the transaction manager implementation. The J2EE SDK implements the
    transaction manager with JTS. But your code doesn‟t call the JTS methods
    directly. Instead, it invokes the JTA methods, which then call the lower-level JTS
    routines. Therefore, JTA is a high level transaction interface that your application
    uses to control transaction. and JTS is a low level transaction interface and ejb
    uses behind the scenes (client code doesn‟t directly interact with JTS. It is based
    on object transaction service(OTS) which is part of CORBA.
20. What is JAXP? - JAXP stands for Java API for XML. XML is a language for
    representing and describing text-based data which can be read and handled by any
    program or tool that uses XML APIs. It provides standard services to determine
    the type of an arbitrary piece of data, encapsulate access to it, discover the
    operations available on it, and create the appropriate JavaBeans component to
    perform those operations.
21. What is J2EE Connector? - The J2EE Connector API is used by J2EE tools
    vendors and system integrators to create resource adapters that support access to
    enterprise information systems that can be plugged into any J2EE product. Each
    type of database or EIS has a different resource adapter. Note: A resource adapter
    is a software component that allows J2EE application components to access and
    interact with the underlying resource manager. Because a resource adapter is
    specific to its resource manager, there is typically a different resource adapter for
    each type of database or enterprise information system.
22. What is JAAP? - The Java Authentication and Authorization Service (JAAS)
    provides a way for a J2EE application to authenticate and authorize a specific user
    or group of users to run it. It is a standard Pluggable Authentication Module
    (PAM) framework that extends the Java 2 platform security architecture to
    support user-based authorization.
23. What is Java Naming and Directory Service? - The JNDI provides naming and
    directory functionality. It provides applications with methods for performing
    standard directory operations, such as associating attributes with objects and
    searching for objects using their attributes. Using JNDI, a J2EE application can
    store and retrieve any type of named Java object. Because JNDI is independent of
    any specific implementations, applications can use JNDI to access multiple
    naming and directory services, including existing naming and
    directory services such as LDAP, NDS, DNS, and NIS.




                                                                                      23
   24. What is Struts? - A Web page development framework. Struts combines Java
       Servlets, Java Server Pages, custom tags, and message resources into a unified
       framework. It is a cooperative, synergistic platform, suitable for development
       teams, independent developers, and everyone between.
   25. How is the MVC design pattern used in Struts framework? - In the MVC
       design pattern, application flow is mediated by a central Controller. The
       Controller delegates requests to an appropriate handler. The handlers are tied to a
       Model, and each handler acts as an adapter between the request and the Model.
       The Model represents, or encapsulates, an application‟s business logic or state.
       Control is usually then forwarded back through the Controller to the appropriate
       View. The forwarding can be determined by consulting a set of mappings, usually
       loaded from a database or configuration file. This provides a loose coupling
       between the View and Model, which can make an application significantly easier
       to create and maintain. Controller: Servlet controller which supplied by Struts
       itself; View: what you can see on the screen, a JSP page and presentation
       components; Model: System state and a business logic JavaBeans.

Basic Java servlet interview questions

   1. What is the difference between CGI and Servlet?
   2. What is meant by a servlet?
   3. What are the types of servlets? What is the difference between 2 types of
       Servlets?
   4. What is the type of method for sending request from HTTP server ?
   5. What are the exceptions thrown by Servlets? Why?
   6. What is the life cycle of a servlet?
   7. What is meant by cookies? Why is Cookie used?
   8. What is HTTP Session?
   9. What is the difference between GET and POST methods?
   10. How can you run a Servlet Program?
   11. What is the middleware? What is the functionality of Webserver?
   12. What webserver is used for running the Servlets?
   13. How do you invoke a Servelt? What is the difference in between doPost and
       doGet methods?
   14. What is the difference in between the HTTPServlet and Generic Servlet? Explain
       their methods? Tell me their parameter names also?
   15. What are session variable in Servlets?
   16. What is meant by Session? Tell me something about HTTPSession Class?
   17. What is Session Tracking?
   18. Difference between doGet and doPost?
   19. What are the methods in HttpServlet?
   20. What are the types of SessionTracking? Why do you use Session Tracking in
       HttpServlet?

Java AWT interview questions



                                                                                       24
Thanks to Sachin Rastogi for contributing these.

   1. What is meant by Controls and what are different types of controls? -
      Controls are componenets that allow a user to interact with your application. The
      AWT supports the following types of controls:
         o Labels
         o Push buttons
         o Check boxes
         o Choice lists
         o Lists
         o Scroll bars
         o Text components

       These controls are subclasses of Component.

   2. Which method of the component class is used to set the position and the size
      of a component? - setBounds(). The following code snippet explains this:
           3.     txtName.setBounds(x,y,width,height);

       places upper left corner of the text field txtName at point (x,y) with the width and
       height of the text field set as width and height.

   4. Which TextComponent method is used to set a TextComponent to the read-
      only state? - setEditable()
   5. How can the Checkbox class be used to create a radio button? - By
      associating Checkbox objects with a CheckboxGroup.
   6. What methods are used to get and set the text label displayed by a Button
      object? - getLabel( ) and setLabel( )
   7. What is the difference between a Choice and a List? - Choice: A Choice is
      displayed in a compact form that requires you to pull it down to see the list of
      available choices. Only one item may be selected from a Choice. List: A List may
      be displayed in such a way that several List items are visible. A List supports the
      selection of one or more List items.
   8. What is the difference between a Scollbar and a Scrollpane? - A Scrollbar is a
      Component, but not a Container. A Scrollpane is a Container and handles its own
      events and performs its own scrolling.
   9. Which are true about the Container class?
          o The validate( ) method is used to cause a Container to be laid out and
              redisplayed.
          o The add( ) method is used to add a Component to a Container.
          o The getBorder( ) method returns information about a Container‟s insets.
          o getComponent( ) method is used to access a Component that is contained
              in a Container.

       Answers: a, b and d




                                                                                         25
10. Suppose a Panel is added to a Frame and a Button is added to the Panel. If
    the Frame‟s font is set to 12-point TimesRoman, the Panel‟s font is set to 10-
    point TimesRoman, and the Button‟s font is not set, what font will be used to
    display the Button‟s label?
        o 12-point TimesRoman
        o 11-point TimesRoman
        o 10-point TimesRoman
        o 9-point TimesRoman

   Answer: c.

11. What are the subclasses of the Container class? - The Container class has three
    major subclasses. They are:
        o Window
        o Panel
        o ScrollPane
12. Which object is needed to group Checkboxes to make them exclusive? -
    CheckboxGroup.
13. What are the types of Checkboxes and what is the difference between them?
    - Java supports two types of Checkboxes:
        o Exclusive
        o Non-exclusive.

   In case of exclusive Checkboxes, only one among a group of items can be
   selected at a time. I f an item from the group is selected, the checkbox currently
   checked is deselected and the new selection is highlighted. The exclusive
   Checkboxes are also called as Radio buttons. The non-exclusive checkboxes are
   not grouped together and each one can be selected independent of the other.

14. What is a Layout Manager and what are the different Layout Managers
    available in java.awt and what is the default Layout manager for the panel
    and the panel subclasses? - A layout Manager is an object that is used to
    organize components in a container. The different layouts available in java.awt
    are:
         o FlowLayout: The elements of a FlowLayout are organized in a top to
           bottom, left to right fashion.
         o BorderLayout: The elements of a BorderLayout are organized at the
           borders (North, South, East and West) and the center of a container.
         o CardLayout: The elements of a CardLayout are stacked, one on top of the
           other, like a deck of cards.
         o GridLayout: The elements of a GridLayout are of equal size and are laid
           out using the square of a grid.
         o GridBagLayout:
           The elements of a GridBagLayout are organized according to a
           grid.However, the elements are of different sizes and may occupy more




                                                                                    26
                than one row or column of the grid. In addition, the rows and columns
                may have different sizes.

         The default Layout Manager of Panel and Panel sub classes is FlowLayout.

   15. Can I add the same component to more than one container? - No. Adding a
       component to a container automatically removes it from any previous parent
       (container).
   16. How can we create a borderless window? - Create an instance of the Window
       class, give it a size, and show it on the screen.
   17.    Frame aFrame = new Frame();
   18.    Window aWindow = new Window(aFrame);
   19.    aWindow.setLayout(new FlowLayout());
   20.    aWindow.add(new Button("Press Me"));
   21.    aWindow.getBounds(50,50,200,200);
   22.    aWindow.show();
   23. Can I create a non-resizable windows? If so, how? - Yes. By using
       setResizable() method in class Frame.
   24. Which containers use a BorderLayout as their default layout? Which
       containers use a FlowLayout as their default layout? - The Window, Frame
       and Dialog classes use a BorderLayout as their default layout. The Panel and the
       Applet classes use the FlowLayout as their default layout.
   25. How do you change the current layout manager for a container?
           o Use the setLayout method
           o Once created you cannot change the current layout manager of a
              component
           o Use the setLayoutManager method
           o Use the updateLayout method

         Answer: a.

   26. What is the difference between a MenuItem and a CheckboxMenuItem?- The
       CheckboxMenuItem class extends the MenuItem class to support a menu item
       that may be checked or unchecked.

Java applet interview questions

Thanks to Sachin Rastogi for sending this set in.

   1. What is an Applet? Should applets have constructors?
      - Applets are small programs transferred through Internet, automatically installed
      and run as part of web-browser. Applets implements functionality of a client.
      Applet is a dynamic and interactive program that runs inside a Web page
      displayed by a Java-capable browser. We don‟t have the concept of Constructors
      in Applets. Applets can be invoked either through browser or through
      Appletviewer utility provided by JDK.




                                                                                        27
2. What are the Applet‟s Life Cycle methods? Explain them? - Following are
   methods in the life cycle of an Applet:
      o init() method - called when an applet is first loaded. This method is called
           only once in the entire cycle of an applet. This method usually intialize the
           variables to be used in the applet.
      o start( ) method - called each time an applet is started.
      o paint() method - called when the applet is minimized or refreshed. This
           method is used for drawing different strings, figures, and images on the
           applet window.
      o stop( ) method - called when the browser moves off the applet‟s page.
      o destroy( ) method - called when the browser is finished with the applet.
3. What is the sequence for calling the methods by AWT for applets? - When an
   applet begins, the AWT calls the following methods, in this sequence:
      o init()
      o start()
      o paint()

   When an applet is terminated, the following sequence of method calls takes place
   :

       o    stop()
       o    destroy()
4. How do Applets differ from Applications? - Following are the main
   differences: Application: Stand Alone, doesn‟t need
   web-browser. Applet: Needs no explicit installation on local machine. Can be
   transferred through Internet on to the local machine and may run as part of web-
   browser. Application: Execution starts with main() method. Doesn‟t work if main
   is not there. Applet: Execution starts with init() method. Application: May or
   may not be a GUI. Applet: Must run within a GUI (Using AWT). This is essential
   feature of applets.
5. Can we pass parameters to an applet from HTML page to an applet? How? -
   We can pass parameters to an applet using <param> tag in the following way:
       o <param name="param1″ value="value1″>
       o <param name="param2″ value="value2″>

   Access those parameters inside the applet is done by calling getParameter()
   method inside the applet. Note that getParameter() method returns String value
   corresponding to the parameter name.

6. How do we read number information from my applet‟s parameters, given
   that Applet‟s getParameter() method returns a string?
   - Use the parseInt() method in the Integer Class, the Float(String) constructor or
   parseFloat() method in the Class Float, or the
   Double(String) constructor or parseDoulbl() method in the class Double.
7. How can I arrange for different applets on a web page to communicate with
   each other?



                                                                                     28
   - Name your applets inside the Applet tag and invoke AppletContext‟s
   getApplet() method in your applet code to obtain references to the
   other applets on the page.
8. How do I select a URL from my Applet and send the browser to that page? -
   Ask the applet for its applet context and invoke showDocument() on that context
   object.
9.      URL targetURL;
10.     String URLString
11.     AppletContext context = getAppletContext();
12.     try
13.     {
14.             targetURL = new URL(URLString);
15.     }
16.     catch (MalformedURLException e)
17.     {
18.             // Code for recover from the exception
19.     }
20.     context. showDocument (targetURL);
21. Can applets on different pages communicate with each other?
    - No, Not Directly. The applets will exchange the information at one meeting
    place either on the local file system or at remote system.
22. How do I determine the width and height of my application?
    - Use the getSize() method, which the Applet class inherits from the Component
    class in the Java.awt package. The getSize() method returns the size of the applet
    as a Dimension object, from which you extract separate width, height fields. The
    following code snippet explains this:
         23.     Dimension dim = getSize();
         24.     int appletwidth = dim.width();
         25.     int appletheight = dim.height();
26. Which classes and interfaces does Applet class consist? - Applet class consists
    of a single class, the Applet class and three interfaces: AppletContext,
    AppletStub, and AudioClip.
27. What is AppletStub Interface?
    - The applet stub interface provides the means by which an applet and the browser
    communicate. Your code will not typically implement this interface.
28. What tags are mandatory when creating HTML to display an applet?
        1. name, height, width
        2. code, name
        3. codebase, height, width
        4. code, height, width

      Correct answer is d.

29. What are the Applet‟s information methods?
    - The following are the Applet‟s information methods: getAppletInfo() method:
    Returns a string describing the applet, its author, copyright information, etc.
    getParameterInfo( ) method: Returns an array of string describing the applet‟s
    parameters.



                                                                                      29
   30. What are the steps involved in Applet development? - Following are the steps
       involved in Applet development:
          o Create/Edit a Java source file. This file must contain a class which extends
               Applet class.
          o Compile your program using javac
          o Execute the appletviewer, specifying the name of your applet‟s source file
               or html file. In case the applet information is stored in html file then
               Applet can be invoked using java enabled web browser.
   31. Which method is used to output a string to an applet? Which function is this
       method included in? - drawString( ) method is used to output a string to an
       applet. This method is included in the paint method of the Applet.

Servlet interview questions

   1. What is a servlet?
      Servlets are modules that extend request/response-oriented servers,such as Java-
      enabled web servers. For example, a servlet might be responsible for taking data
      in an HTML order-entry form and applying the business logic used to update a
      company‟s order database. Servlets are to servers what applets are to browsers.
      Unlike applets, however, servlets have no graphical user interface.
   2. Whats the advantages using servlets over using CGI?
      Servlets provide a way to generate dynamic documents that is both easier to write
      and faster to run. Servlets also address the problem of doing server-side
      programming with platform-specific APIs: they are developed with the Java
      Servlet API, a standard Java extension.
   3. What are the general advantages and selling points of Servlets?
      A servlet can handle multiple requests concurrently, and synchronize requests.
      This allows servlets to support systems such as online
      real-time conferencing. Servlets can forward requests to other servers and
      servlets. Thus servlets can be used to balance load among several servers that
      mirror the same content, and to partition a single logical service over several
      servers, according to task type or organizational boundaries.
   4. Which package provides interfaces and classes for writing servlets? javax
   5. What‟s the Servlet Interface?
      The central abstraction in the Servlet API is the Servlet interface. All servlets
      implement this interface, either directly or, more
      commonly, by extending a class that implements it such as HttpServlet.Servlets >
      Generic Servlet > HttpServlet > MyServlet.
      The Servlet interface declares, but does not implement, methods that manage the
      servlet and its communications with clients. Servlet writers provide some or all of
      these methods when developing a servlet.
   6. When a servlet accepts a call from a client, it receives two objects. What are
      they?
      ServletRequest (which encapsulates the communication from the client to the
      server) and ServletResponse (which encapsulates the communication from the




                                                                                       30
       servlet back to the client). ServletRequest and ServletResponse are interfaces
       defined inside javax.servlet package.
   7. What information does ServletRequest allow access to?
       Information such as the names of the parameters passed in by the client, the
       protocol (scheme) being used by the client, and the names
       of the remote host that made the request and the server that received it. Also the
       input stream, as ServletInputStream.Servlets use the input stream to get data from
       clients that use application protocols such as the HTTP POST and GET methods.
   8. What type of constraints can ServletResponse interface set on the client?
       It can set the content length and MIME type of the reply. It also provides an
       output stream, ServletOutputStream and a Writer through
       which the servlet can send the reply data.
   9. Explain servlet lifecycle?
       Each servlet has the same life cycle: first, the server loads and initializes the
       servlet (init()), then the servlet handles zero or more client requests (service()),
       after that the server removes the servlet (destroy()). Worth noting that the last step
       on some servers is done when they shut down.
   10. How does HTTP Servlet handle client requests?
       An HTTP Servlet handles client requests through its service method. The service
       method supports standard HTTP client requests by dispatching each request to a
       method designed to handle that request.

JDBC interview questions

Thanks to Sachin Rastogi for sending in Java database interview questions.

   1. What are the steps involved in establishing a JDBC connection? This action
      involves two steps: loading the JDBC driver and making the connection.
   2. How can you load the drivers?
      Loading the driver or drivers you want to use is very simple and involves just one
      line of code. If, for example, you want to use the JDBC-ODBC Bridge driver, the
      following code will load it:

       Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

       Your driver documentation will give you the class name to use. For instance, if
       the class name is jdbc.DriverXYZ, you would load the driver with the following
       line of code:

       Class.forName("jdbc.DriverXYZ");

   3. What will Class.forName do while loading drivers? It is used to create an
      instance of a driver and register it with the
      DriverManager. When you have loaded a driver, it is available for making a
      connection with a DBMS.



                                                                                          31
4. How can you make the connection? To establish a connection you need to have
   the appropriate driver connect to the DBMS.
   The following line of code illustrates the general idea:

   String url = “jdbc:odbc:Fred";
   Connection con = DriverManager.getConnection(url, “Fernanda", “J8?);

5. How can you create JDBC statements and what are they?
   A Statement object is what sends your SQL statement to the DBMS. You simply
   create a Statement object and then execute it, supplying the appropriate execute
   method with the SQL statement you want to send. For a SELECT statement, the
   method to use is executeQuery. For statements that create or modify tables, the
   method to use is executeUpdate. It takes an instance of an active connection to
   create a Statement object. In the following example, we use our Connection object
   con to create the Statement object

   Statement stmt = con.createStatement();

6. How can you retrieve data from the ResultSet?
   JDBC returns results in a ResultSet object, so we need to declare an instance of
   the class ResultSet to hold our results. The following code demonstrates declaring
   the ResultSet object rs.

   ResultSet rs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM
   COFFEES");
   String s = rs.getString("COF_NAME");

   The method getString is invoked on the ResultSet object rs, so getString() will
   retrieve (get) the value stored in the column COF_NAME in the current row of rs.

7. What are the different types of Statements?
   Regular statement (use createStatement method), prepared statement (use
   prepareStatement method) and callable statement (use prepareCall)
8. How can you use PreparedStatement? This special type of statement is derived
   from class Statement.If you need a
   Statement object to execute many times, it will normally make sense to use a
   PreparedStatement object instead. The advantage to this is that in most cases, this
   SQL statement will be sent to the DBMS right away, where it will be compiled.
   As a result, the PreparedStatement object contains not just an SQL statement, but
   an SQL statement that has been precompiled. This means that when the
   PreparedStatement is executed, the DBMS can just run the PreparedStatement‟s
   SQL statement without having to compile it first.
       9.       PreparedStatement updateSales =
       10.              con.prepareStatement("UPDATE COFFEES SET SALES =
             ? WHERE COF_NAME LIKE ?");
11. What does setAutoCommit do?
    When a connection is created, it is in auto-commit mode. This means that each


                                                                                    32
   individual SQL statement is treated as a transaction and will be automatically
   committed right after it is executed. The way to allow two or more statements to
   be grouped into a transaction is to disable auto-commit mode:

   con.setAutoCommit(false);

   Once auto-commit mode is disabled, no SQL statements will be committed until
   you call the method commit explicitly.

   con.setAutoCommit(false);
   PreparedStatement updateSales =
     con.prepareStatement( "UPDATE COFFEES SET SALES = ? WHERE
   COF_NAME LIKE ?");
   updateSales.setInt(1, 50); updateSales.setString(2, "Colombian");
   updateSales.executeUpdate();
   PreparedStatement updateTotal =
     con.prepareStatement("UPDATE COFFEES SET TOTAL = TOTAL + ? WHERE
   COF_NAME LIKE ?");
   updateTotal.setInt(1, 50);
   updateTotal.setString(2, "Colombian");
   updateTotal.executeUpdate();
   con.commit();
   con.setAutoCommit(true);

12. How do you call a stored procedure from JDBC?
    The first step is to create a CallableStatement object. As with Statement an and
    PreparedStatement objects, this is done with an open
    Connection object. A CallableStatement object contains a call to a stored
    procedure.
       13.            CallableStatement cs = con.prepareCall("{call
           SHOW_SUPPLIERS}");
       14.            ResultSet rs = cs.executeQuery();
15. How do I retrieve warnings?
    SQLWarning objects are a subclass of SQLException that deal with database
    access warnings. Warnings do not stop the execution of an
    application, as exceptions do; they simply alert the user that something did not
    happen as planned. A warning can be reported on a
    Connection object, a Statement object (including PreparedStatement and
    CallableStatement objects), or a ResultSet object. Each of these
    classes has a getWarnings method, which you must invoke in order to see the first
    warning reported on the calling object:
       16.    SQLWarning warning = stmt.getWarnings();
       17.    if (warning != null)
       18.    {
       19.            System.out.println("n---Warning---n");
       20.            while (warning != null)
       21.            {
       22.                    System.out.println("Message: " +
           warning.getMessage());
       23.                    System.out.println("SQLState: " +
           warning.getSQLState());



                                                                                       33
       24.                        System.out.print("Vendor error code: ");
       25.
               System.out.println(warning.getErrorCode());
       26.                    System.out.println("");
       27.                    warning = warning.getNextWarning();
       28.             }
       29.     }
30. How can you move the cursor in scrollable result sets?
    One of the new features in the JDBC 2.0 API is the ability to move a result set‟s
    cursor backward as well as forward. There are also methods that let you move the
    cursor to a particular row and check the position of the cursor.

   Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
   ResultSet.CONCUR_READ_ONLY);
   ResultSet srs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM
   COFFEES");

   The first argument is one of three constants added to the ResultSet API to indicate
   the type of a ResultSet object: TYPE_FORWARD_ONLY,
   TYPE_SCROLL_INSENSITIVE , and TYPE_SCROLL_SENSITIVE. The
   second argument is one of two ResultSet constants for specifying whether a result
   set is read-only or updatable: CONCUR_READ_ONLY and
   CONCUR_UPDATABLE. The point to remember here is that if you specify a
   type, you must also specify whether it is read-only or updatable. Also, you must
   specify the type first, and because both parameters are of type int , the compiler
   will not complain if you switch the order. Specifying the constant
   TYPE_FORWARD_ONLY creates a nonscrollable result set, that is, one in
   which the cursor moves only forward. If you do not specify any constants for the
   type and updatability of a ResultSet object, you will automatically get one that is
   TYPE_FORWARD_ONLY and CONCUR_READ_ONLY.

31. What‟s the difference between TYPE_SCROLL_INSENSITIVE , and
    TYPE_SCROLL_SENSITIVE?
    You will get a scrollable ResultSet object if you specify one of these ResultSet
    constants.The difference between the two has to do with whether a result set
    reflects changes that are made to it while it is open and whether certain methods
    can be called to detect these changes. Generally speaking, a result set that is
    TYPE_SCROLL_INSENSITIVE does not reflect changes made while it is still
    open and one that is TYPE_SCROLL_SENSITIVE does. All three types of result
    sets will make changes visible if they are closed and then reopened:
       32.    Statement stmt =
       33.            con.createStatement(ResultSet.TYPE_SCROLL_INSENSI
           TIVE, ResultSet.CONCUR_READ_ONLY);
       34.    ResultSet srs =
       35.            stmt.executeQuery("SELECT COF_NAME, PRICE FROM
           COFFEES");
       36.    srs.afterLast();
       37.    while (srs.previous())
       38.    {



                                                                                   34
          39.               String name = srs.getString("COF_NAME");
          40.               float price = srs.getFloat("PRICE");
          41.               System.out.println(name + " " + price);
          42.     }
   43. How to Make Updates to Updatable Result Sets?
       Another new feature in the JDBC 2.0 API is the ability to update rows in a result
       set using methods in the Java programming language rather than having to send
       an SQL command. But before you can take advantage of this capability, you need
       to create a ResultSet object that is updatable. In order to do this, you supply the
       ResultSet constant CONCUR_UPDATABLE to the createStatement method.
          44.    Connection con =
          45.            DriverManager.getConnection("jdbc:mySubprotocol:m
              ySubName");
          46.    Statement stmt =
          47.            con.createStatement(ResultSet.TYPE_SCROLL_SENSITI
              VE, ResultSet.CONCUR_UPDATABLE);
          48.    ResultSet uprs =
          49.            stmt.executeQuery("SELECT COF_NAME, PRICE FROM
              COFFEES");

Java interview questions

   1. What are synchronized methods and synchronized statements? Synchronized
      methods are methods that are used to control access to an object. For example, a
      thread only executes a synchronized method after it has acquired the lock for the
      method‟s object or class. Synchronized statements are similar to synchronized
      methods. A synchronized statement can only be executed after a thread has
      acquired the lock for the object or class referenced in the synchronized statement.
   2. What are different ways in which a thread can enter the waiting state? A
      thread can enter the waiting state by invoking its sleep() method, blocking on I/O,
      unsuccessfully attempting to acquire an object‟s lock, or invoking an object‟s
      wait() method. It can also enter the waiting state by invoking its (deprecated)
      suspend() method.
   3. Can a lock be acquired on a class? Yes, a lock can be acquired on a class. This
      lock is acquired on the class‟s Class object.
   4. What‟s new with the stop(), suspend() and resume() methods in new JDK
      1.2? The stop(), suspend() and resume() methods have been deprecated in JDK
      1.2.
   5. What is the preferred size of a component? The preferred size of a component
      is the minimum component size that will allow the component to display
      normally.
   6. What method is used to specify a container‟s layout? The setLayout() method
      is used to specify a container‟s layout. For example, setLayout(new
      FlowLayout()); will be set the layout as FlowLayout.
   7. Which containers use a FlowLayout as their default layout? The Panel and
      Applet classes use the FlowLayout as their default layout.
   8. What state does a thread enter when it terminates its processing? When a
      thread terminates its processing, it enters the dead state.



                                                                                        35
9. What is the Collections API? The Collections API is a set of classes and
    interfaces that support operations on collections of objects. One example of class
    in Collections API is Vector and Set and List are examples of interfaces in
    Collections API.
10. What is the List interface? The List interface provides support for ordered
    collections of objects. It may or may not allow duplicate elements but the
    elements must be ordered.
11. How does Java handle integer overflows and underflows? It uses those low
    order bytes of the result that can fit into the size of the type allowed by the
    operation.
12. What is the Vector class? The Vector class provides the capability to implement
    a growable array of objects. The main visible advantage of this class is
    programmer needn‟t to worry about the number of elements in the Vector.
13. What modifiers may be used with an inner class that is a member of an outer
    class? A (non-local) inner class may be declared as public, protected, private,
    static, final, or abstract.
14. If a method is declared as protected, where may the method be accessed? A
    protected method may only be accessed by classes or interfaces of the same
    package or by subclasses of the class in which it is declared.
15. What is an Iterator interface? The Iterator interface is used to step through the
    elements of a Collection.
16. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8
    characters? Unicode requires 16 bits, ASCII require 7 bits (although the ASCII
    character set uses only 7 bits, it is usually represented as 8 bits), UTF-8 represents
    characters using 8, 16, and 18 bit patterns, UTF-16 uses 16-bit and larger bit
    patterns
17. What is the difference between yielding and sleeping? Yielding means a thread
    returning to a ready state either from waiting, running or after creation, where as
    sleeping refers a thread going to a waiting state from running state. With reference
    to Java, when a task invokes its yield() method, it returns to the ready state and
    when a task invokes its sleep() method, it returns to the waiting state
18. What are wrapper classes? Wrapper classes are classes that allow primitive
    types to be accessed as objects. For example, Integer, Double. These classes
    contain many methods which can be used to manipulate basic data types
19. Does garbage collection guarantee that a program will not run out of
    memory? No, it doesn‟t. It is possible for programs to use up memory resources
    faster than they are garbage collected. It is also possible for programs to create
    objects that are not subject to garbage collection. The main purpose of Garbage
    Collector is recover the memory from the objects which are no longer required
    when more memory is needed.
20. Name Component subclasses that support painting? The following classes
    support painting: Canvas, Frame, Panel, and Applet.
21. What is a native method? A native method is a method that is implemented in a
    language other than Java. For example, one method may be written in C and can
    be called in Java.
22. How can you write a loop indefinitely?



                                                                                       36
   for(;;) //for loop
   while(true); //always true

23. Can an anonymous class be declared as implementing an interface and
    extending a class? An anonymous class may implement an interface or extend a
    superclass, but may not be declared to do both.
24. What is the purpose of finalization? The purpose of finalization is to give an
    unreachable object the opportunity to perform any cleanup processing before the
    object is garbage collected. For example, closing a opened file, closing a opened
    database Connection.
25. What invokes a thread‟s run() method? After a thread is started, via its start()
    method or that of the Thread class, the JVM invokes the thread‟s run() method
    when the thread is initially executed.
26. What is the GregorianCalendar class? The GregorianCalendar provides support
    for traditional Western calendars.
27. What is the SimpleTimeZone class? The SimpleTimeZone class provides
    support for a Gregorian calendar.
28. What is the Properties class? The properties class is a subclass of Hashtable that
    can be read from or written to a stream. It also provides the capability to specify a
    set of default values to be used.
29. What is the purpose of the Runtime class? The purpose of the Runtime class is
    to provide access to the Java runtime system.
30. What is the purpose of the System class? The purpose of the System class is to
    provide access to system resources.
31. What is the purpose of the finally clause of a try-catch-finally statement? The
    finally clause is used to provide the capability to execute code no matter whether
    or not an exception is thrown or caught. For example,

   try
   {
   //some statements
   }
   catch
   {
   // statements when exception is cought
   }
   finally
   {
   //statements executed whether exception occurs or not
   }

32. What is the Locale class? The Locale class is used to tailor program output to
    the conventions of a particular geographic, political, or cultural region.
33. What must a class do to implement an interface? It must provide all of the
    methods in the interface and identify the interface in its implements clause.




                                                                                      37
JSP interview questions

   1. What is JSP? Describe its concept. JSP is a technology that combines
      HTML/XML markup languages and elements of Java programming Language to
      return dynamic content to the Web client, It is normally used to handle
      Presentation logic of a web application, although it may have business logic.
   2. What are the lifecycle phases of a JSP?
      JSP page looks like a HTML page but is a servlet. When presented with JSP page
      the JSP engine does the following 7 phases.
          1. Page translation: -page is parsed, and a java file which is a servlet is
               created.
          2. Page compilation: page is compiled into a class file
          3. Page loading : This class file is loaded.
          4. Create an instance :- Instance of servlet is created
          5. jspInit() method is called
          6. _jspService is called to handle service calls
          7. _jspDestroy is called to destroy it when the servlet is not required.
   3. What is a translation unit? JSP page can include the contents of other HTML
      pages or other JSP files. This is done by using the include directive. When the JSP
      engine is presented with such a JSP page it is converted to one servlet class and
      this is called a translation unit, Things to remember in a translation unit is that
      page directives affect the whole unit, one variable declaration cannot occur in the
      same unit more than once, the standard action jsp:useBean cannot declare the
      same bean twice in one unit.
   4. How is JSP used in the MVC model? JSP is usually used for presentation in the
      MVC pattern (Model View Controller ) i.e. it plays the role of the view. The
      controller deals with calling the model and the business classes which in turn get
      the data, this data is then presented to the JSP for rendering on to the client.
   5. What are context initialization parameters? Context initialization parameters
      are specified by the <context-param> in the web.xml file, these are initialization
      parameter for the whole application and not specific to any servlet or JSP.
   6. What is a output comment? A comment that is sent to the client in the viewable
      page source. The JSP engine handles an output comment as un-interpreted HTML
      text, returning the comment in the HTML output sent to the client. You can see
      the comment by viewing the page source from your Web browser.
   7. What is a Hidden Comment? A comment that documents the JSP page but is
      not sent to the client. The JSP engine ignores a hidden comment, and does not
      process any code within hidden comment tags. A hidden comment is not sent to
      the client, either in the displayed JSP page or the HTML page source. The hidden
      comment is useful when you want to hide or “comment out” part of your JSP
      page.
   8. What is a Expression? Expressions are act as place holders for language
      expression, expression is evaluated each time the page is accessed.
   9. What is a Declaration? It declares one or more variables or methods for use later
      in the JSP source file. A declaration must contain at least one complete
      declarative statement. You can declare any number of variables or methods within


                                                                                      38
    one declaration tag, as long as semicolons separate them. The declaration must be
    valid in the scripting language used in the JSP file.
10. What is a Scriptlet? A scriptlet can contain any number of language statements,
    variable or method declarations, or expressions that are valid in the page scripting
    language. Within scriptlet tags, you can declare variables or methods to use later
    in the file, write expressions valid in the page scripting language, use any of the
    JSP implicit objects or any object declared with a <jsp:useBean>.
11. What are the implicit objects? List them. Certain objects that are available for
    the use in JSP documents without being declared first. These objects are parsed by
    the JSP engine and inserted into the generated servlet. The implicit objects are:
        o request
        o response
        o pageContext
        o session
        o application
        o out
        o config
        o page
        o exception
12. What‟s the difference between forward and sendRedirect? When you invoke a
    forward request, the request is sent to another resource on the server, without the
    client being informed that a different resource is going to process the request. This
    process occurs completely with in the web container And then returns to the
    calling method. When a sendRedirect method is invoked, it causes the web
    container to return to the browser indicating that a new URL should be requested.
    Because the browser issues a completely new request any object that are stored as
    request attributes before the redirect occurs will be lost. This extra round trip a
    redirect is slower than forward.
13. What are the different scope values for the <jsp:useBean>? The different
    scope values for <jsp:useBean> are:
        o page
        o request
        o session
        o application
14. Why are JSP pages the preferred API for creating a web-based client
    program? Because no plug-ins or security policy files are needed on the client
    systems(applet does). Also, JSP pages enable cleaner and more module
    application design because they provide a way to separate applications
    programming from web page design. This means personnel involved in web page
    design do not need to understand Java programming language syntax to do their
    jobs.
15. Is JSP technology extensible? Yes, it is. JSP technology is extensible through
    the development of custom actions, or tags, which are encapsulated in tag
    libraries.
16. What is difference between custom JSP tags and beans? Custom JSP tag is a
    tag you defined. You define how a tag, its attributes and its body are interpreted,



                                                                                      39
      and then group your tags into collections called tag libraries that can be used in
      any number of JSP files. Custom tags and beans accomplish the same goals –
      encapsulating complex behavior into simple and accessible forms. There are
      several differences:
         o Custom tags can manipulate JSP content; beans cannot.
         o Complex operations can be reduced to a significantly simpler form with
              custom tags than with beans.
         o Custom tags require quite a bit more work to set up than do beans.
         o Custom tags usually define relatively self-contained behavior, whereas
              beans are often defined in one servlet and used in a different servlet or JSP
              page.
         o Custom tags are available only in JSP 1.1 and later, but beans can be used
              in all JSP 1.x versions.

Java interview questions

   1. What is a class? A class is a blueprint, or prototype, that defines the variables
      and the methods common to all objects of a certain kind.
   2. What is a object? An object is a software bundle of variables and related
      methods.An instance of a class depicting the state and behavior at that particular
      time in real world.
   3. What is a method? Encapsulation of a functionality which can be called to
      perform specific tasks.
   4. What is encapsulation? Explain with an example. Encapsulation is the term
      given to the process of hiding the implementation details of the object. Once an
      object is encapsulated, its implementation details are not immediately accessible
      any more. Instead they are packaged and are only indirectly accessible via the
      interface of the object
   5. What is inheritance? Explain with an example. Inheritance in object oriented
      programming means that a class of objects can inherit properties and methods
      from another class of objects.
   6. What is polymorphism? Explain with an example. In object-oriented
      programming, polymorphism refers to a programming language‟s ability to
      process objects differently depending on their data type or class. More
      specifically, it is the ability to redefine methods for derived classes. For example,
      given a base class shape, polymorphism enables the programmer to define
      different area methods for any number of derived classes, such as circles,
      rectangles and triangles. No matter what shape an object is, applying the area
      method to it will return the correct results. Polymorphism is considered to be a
      requirement of any true object-oriented programming language
   7. Is multiple inheritance allowed in Java? No, multiple inheritance is not allowed
      in Java.
   8. What is interpreter and compiler? Java interpreter converts the high level
      language code into a intermediate form in Java called as bytecode, and then
      executes it, where as a compiler converts the high level language code to machine
      language making it very hardware specific


                                                                                        40
9. What is JVM? The Java interpreter along with the runtime environment required
    to run the Java application in called as Java virtual machine(JVM)
10. What are the different types of modifiers? There are access modifiers and there
    are other identifiers. Access modifiers are public, protected and private. Other are
    final and static.
11. What are the access modifiers in Java? There are 3 access modifiers. Public,
    protected and private, and the default one if no identifier is specified is called
    friendly, but programmer cannot specify the friendly identifier explicitly.
12. What is a wrapper class? They are classes that wrap a primitive data type so it
    can be used as a object
13. What is a static variable and static method? What‟s the difference between
    two? The modifier static can be used with a variable and method. When declared
    as static variable, there is only one variable no matter how instances are created,
    this variable is initialized when the class is loaded. Static method do not need a
    class to be instantiated to be called, also a non static method cannot be called from
    static method.
14. What is garbage collection? Garbage Collection is a thread that runs to reclaim
    the memory by destroying the objects that cannot be referenced anymore.
15. What is abstract class? Abstract class is a class that needs to be extended and its
    methods implemented, aclass has to be declared abstract if it has one or more
    abstract methods.
16. What is meant by final class, methods and variables? This modifier can be
    applied to class method and variable. When declared as final class the class
    cannot be extended. When declared as final variable, its value cannot be changed
    if is primitive value, if it is a reference to the object it will always refer to the
    same object, internal attributes of the object can be changed.
17. What is interface? Interface is a contact that can be implemented by a class, it
    has method that need implementation.
18. What is method overloading? Overloading is declaring multiple method with
    the same name, but with different argument list.
19. What is method overriding? Overriding has same method name, identical
    arguments used in subclass.
20. What is singleton class? Singleton class means that any given time only one
    instance of the class is present, in one JVM.
21. What is the difference between an array and a vector? Number of elements in
    an array are fixed at the construction time, whereas the number of elements in
    vector can grow dynamically.
22. What is a constructor? In Java, the class designer can guarantee initialization of
    every object by providing a special method called a constructor. If a class has a
    constructor, Java automatically calls that constructor when an object is created,
    before users can even get their hands on it. So initialization is guaranteed.
23. What is casting? Conversion of one type of data to another when appropriate.
    Casting makes explicitly converting of data.
24. What is the difference between final, finally and finalize? The modifier final is
    used on class variable and methods to specify certain behaviour explained above.
    And finally is used as one of the loop in the try catch blocks, It is used to hold



                                                                                      41
      code that needs to be executed whether or not the exception occurs in the try catch
      block. Java provides a method called finalize( ) that can be defined in the class.
      When the garbage collector is ready to release the storage ed for your object, it
      will first call finalize( ), and only on the next garbage-collection pass will it
      reclaim the objects memory. So finalize( ), gives you the ability to perform some
      important cleanup at the time of garbage collection.
  25. What is are packages? A package is a collection of related classes and interfaces
      providing access protection and namespace management.
  26. What is a super class and how can you call a super class? When a class is
      extended that is derived from another class there is a relationship is created, the
      parent class is referred to as the super class by the derived class that is the child.
      The derived class can make a call to the super class using the keyword super. If
      used in the constructor of the derived class it has to be the first statement.
  27. What is meant by a Thread? Thread is defined as an instantiated parallel
      process of a given program.
  28. What is multi-threading? Multi-threading as the name suggest is the scenario
      where more than one threads are running.
  29. What are two ways of creating a thread? Which is the best way and why?
      Two ways of creating threads are, one can extend from the Java.lang.Thread and
      can implement the rum method or the run method of a different class can be
      called which implements the interface Runnable, and the then implement the run()
      method. The latter one is mostly used as first due to Java rule of only one class
      inheritance, with implementing the Runnable interface that problem is sorted out.
  30. What is deadlock? Deadlock is a situation when two threads are waiting on each
      other to release a resource. Each thread waiting for a resource which is held by the
      other waiting thread. In Java, this resource is usually the object lock obtained by
      the synchronized keyword.
  31. What are the three types of priority? MAX_PRIORITY which is 10,
      MIN_PRIORITY which is 1, NORM_PRIORITY which is 5.
  32. What is the use of synchronizations? Every object has a lock, when a
      synchronized keyword is used on a piece of code the, lock must be obtained by
      the thread first to execute that code, other threads will not be allowed to execute
      that piece of code till this lock is released.

Java networking and algoritms interview questions

  1. What is the protocol used by server and client ?
  2. Can I modify an object in CORBA ?
  3. What is the functionality stubs and skeletons ?

  4.   What is the mapping mechanism used by Java to identify IDL language ?
  5.   Diff between Application and Applet ?
  6.   What is serializable Interface ?
  7.   What is the difference between CGI and Servlet ?
  8.   What is the use of Interface ?
  9.   Why Java is not fully objective oriented ?


                                                                                         42
10. Why does not support multiple Inheritance ?
11. What it the root class for all Java classes ?
12. What is polymorphism ?
13. Suppose If we have variable „ I „ in run method, If I can create one or more thread
    each thread will occupy a separate copy or same variable will be shared ?
14. In servlets, we are having a web page that is invoking servlets username and
    password ? which is checked in the database ? Suppose the second page also If we
    want to verify the same information whether it will connect to the database or it
    will be used previous information?
15. What are virtual functions ?
16. Write down how will you create a binary Tree ?
17. What are the traverses in Binary Tree ?
18. Write a program for recursive Traverse ?
19. What are session variable in Servlets ?
20. What is client server computing ?
21. What is Constructor and Virtual function? Can we call Virtual function in a
    constructor ?
22. Why we use OOPS concepts? What is its advantage ?
23. What is the middleware ? What is the functionality of Webserver ?
24. Why Java is not 100 % pure OOPS ? ( EcomServer )
25. When we will use an Interface and Abstract class ?
26. What is an RMI?
27. How will you pass parameters in RMI ? Why u serialize?
28. What is the exact difference in between Unicast and Multicast object ? Where we
    will use ?
29. What is the main functionality of the Remote Reference Layer ?
30. How do you download stubs from a Remote place ?
31. What is the difference in between C++ and Java ? can u explain in detail ?
32. I want to store more than 10 objects in a remote server ? Which methodology will
    follow ?
33. What is the main functionality of the Prepared Statement ?
34. What is meant by static query and dynamic query ?
35. What are the Normalization Rules ? Define the Normalization ?
36. What is meant by Servlet? What are the parameters of the service method ?
37. What is meant by Session ? Tell me something about HTTPSession Class ?
38. How do you invoke a Servlet? What is the difference in between doPost and
    doGet methods ?
39. What is the difference in between the HTTPServlet and Generic Servlet ? Explain
    their methods ? Tell me their parameter names also ?
40. Have you used threads in Servlet ?
41. Write a program on RMI and JDBC using StoredProcedure ?
42. How do you sing an Applet ?
43. In a Container there are 5 components. I want to display the all the components
    names, how will you do that one ?
44. Why there are some null interface in java ? What does it mean ? Give me some
    null interfaces in JAVA ?



                                                                                    43
   45. Tell me the latest versions in JAVA related areas ?
   46. What is meant by class loader ? How many types are there? When will we use
       them ?
   47. How do you load an Image in a Servlet ?
   48. What is meant by flickering ?
   49. What is meant by distributed Application ? Why we are using that in our
       applications ?
   50. What is the functionality of the stub ?
   51. Have you used any version control ?
   52. What is the latest version of JDBC ? What are the new features are added in that ?
   53. Explain 2 tier and 3 -tier Architecture ?
   54. What is the role of the webserver ?
   55. How have you done validation of the fields in your project ?
   56. What is the main difficulties that you are faced in your project ?
   57. What is meant by cookies ? Explain ?

Large collection of Java interview questions

   1. What is the difference between an Abstract class and Interface ?
   2. What is user defined exception ?
   3. What do you know about the garbage collector ?

   4.  What is the difference between C++ & Java ?
   5.  Explain RMI Architecture?
   6.  How do you communicate in between Applets & Servlets ?
   7.  What is the use of Servlets ?
   8.  What is JDBC? How do you connect to the Database ?
   9.  In an HTML form I have a Button which makes us to open another page in 15
       seconds. How will do you that ?
   10. What is the difference between Process and Threads ?
   11. What is the difference between RMI & Corba ?
   12. What are the services in RMI ?
   13. How will you initialize an Applet ?
   14. What is the order of method invocation in an Applet ?
   15. When is update method called ?
   16. How will you pass values from HTML page to the Servlet ?
   17. Have you ever used HashTable and Dictionary ?
   18. How will you communicate between two Applets ?
   19. What are statements in JAVA ?
   20. What is JAR file ?
   21. What is JNI ?
   22. What is the base class for all swing components ?
   23. What is JFC ?
   24. What is Difference between AWT and Swing ?




                                                                                      44
   25. Considering notepad/IE or any other thing as process, What will happen if you
       start notepad or IE 3 times? Where 3 processes are started or 3 threads are started
       ?
   26. How does thread synchronization occurs inside a monitor ?
   27. How will you call an Applet using a Java Script function ?
   28. Is there any tag in HTML to upload and download files ?
   29. Why do you Canvas ?
   30. How can you push data from an Applet to Servlet ?
   31. What are 4 drivers available in JDBC ?
   32. How you can know about drivers and database information ?
   33. If you are truncated using JDBC, How can you know ..that how much data is
       truncated ?
   34. And What situation , each of the 4 drivers used ?
   35. How will you perform transaction using JDBC ?
   36. In RMI, server object first loaded into the memory and then the stub reference is
       sent to the client ? or whether a stub reference is directly sent to the client ?
   37. Suppose server object is not loaded into the memory, and the client request for it ,
       what will happen?
   38. What is serialization ?
   39. Can you load the server object dynamically? If so, what are the major 3 steps
       involved in it ?
   40. What is difference RMI registry and OSAgent ?
   41. To a server method, the client wants to send a value 20, with this value exceeds to
       20,. a message should be sent to the client ? What will you do for achieving for
       this ?
   42. What are the benefits of Swing over AWT ?
   43. Where the CardLayout is used ?
   44. What is the Layout for ToolBar ?
   45. What is the difference between Grid and GridbagLayout ?
   46. How will you add panel to a Frame ?
   47. What is the corresponding Layout for Card in Swing ?
   48. What is light weight component ?
   49. Can you run the product development on all operating systems ?
   50. What is the webserver used for running the Servlets ?
   51. What is Servlet API used for connecting database ?
   52. What is bean ? Where it can be used ?
   53. What is difference in between Java Class and Bean ?
   54. Can we send object using Sockets ?
   55. What is the RMI and Socket ?
   56. How to communicate 2 threads each other ?
   57. What are the files generated after using IDL to Java Compilet ?

What is a platform?
A platform is the hardware or software environment in which a program runs.
Most platforms can be described as a combination of the operating system and
hardware, like Windows 2000/XP, Linux, Solaris, and MacOS.



                                                                                        45
What is the main difference between Java platform and other platforms?
The Java platform differs from most other platforms in that it\‟s a
software-only platform that runs on top of other hardware-based platforms.

The Java platform has two components:

The Java Virtual Machine (Java VM)
The Java Application Programming Interface (Java API)

What is the Java Virtual Machine?
The Java Virtual Machine is a software that can be ported onto various
hardware-based platforms.

What is the Java API?
The Java API is a large collection of ready-made software components that
provide many useful capabilities, such as graphical user interface (GUI)
widgets.

What is the package?
The package is a Java namespace or part of Java libraries. The Java API is
grouped into libraries of related classes and interfaces; these libraries are
known as packages.

What is native code?
The native code is code that after you compile it, the compiled code runs
on a specific hardware platform.

Is Java code slower than native code?
Not really. As a platform-independent environment, the Java platform can be
a bit slower than native code. However, smart compilers, well-tuned
interpreters, and just-in-time bytecode compilers can bring performance close
to that of native code without threatening portability.

What is the serialization?
The serialization is a kind of mechanism that makes a class or a bean
persistence by having its properties or fields and state information saved and
restored to and from storage.

How to make a class or a bean serializable?
By implementing either the java.io.Serializable interface, or the
java.io.Externalizable interface. As long as one class in a class\‟s
inheritance hierarchy implements Serializable or Externalizable, that class is
serializable.

How many methods in the Serializable interface?
There is no method in the Serializable interface. The Serializable


                                                                                 46
interface acts as a marker, telling the object serialization tools that your
class is serializable.

How many methods in the Externalizable interface?
There are two methods in the Externalizable interface. You have to
implement these two methods in order to make your class externalizable. These
two methods are readExternal() and writeExternal().

What is the difference between Serializalble and Externalizable interface?

When you use Serializable interface, your class is serialized automatically
by default. But you can override writeObject() and readObject() two methods to
control more complex object serailization process. When you use Externalizable
interface, you have a complete control over your class\‟s serialization
process.

What is a transient variable?
A transient variable is a variable that may not be serialized. If you don\‟t
want some field not to be serialized, you can mark that field transient or
static.

Which containers use a border layout as their default layout?
The window, Frame and Dialog classes use a border layout as their default
layout.

How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers.
When an Observable object is updated it invokes the update() method of each of
its observers to notify the observers that it has changed state. The Observer
interface is implemented by objects that observe Observable objects.

What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to
control the access of multiple threads to shared resources. Without
synchronization, it is possible for one thread to modify a shared object while
another thread is in the process of using or updating that object\‟s value.
This often causes dirty data and leads to significant errors.

Is Java a super set of JavaScript?
No. They are completely different. Some syntax may be similar.

What is user defined exception?
Ans: There are many exception defined by java which are used to track the run time
exceptions and act accordingly. User can also define his exceptions that can be thrown in
the same way java exceptions.




                                                                                       47
What do you know about the garbage collector?
Ans: Garbage collector is used to recollect memory from the us=nused objects. They are
the objects that are no longer needed because of function or class scope is going to finish.

Explain RMI Architecture?
Ans: Sometimes it is necessary to invoke a method of an object that is being executed on
a remote machine as part of distributed computing. This shares computation between 2
machines. Fortunately java has provided this mechanism. This mechanism is called RMI.

What is the use of Servlets?
Ans: Servlets are used as a middleware and contains the whole business logic and keep
client and server free with their presentation and data processing parts respectively. They
are mainly used in web projects where many clients are requesting the service from the
server. The communication always takes place through servlets.

What is JDBC? How do you connect to the Database?
Ans: Java Database Connectivity is a technique of connect java front end to back end
database and allowing the retrieval and manipulation of data in the database using java.
The process of using JDBC to connect to the database is as follows:
1. Register the driver: Class.forName(\"driverName\")// for example,
sun.jdbc.odbc.JdbcOdbcDriver
2. Making the connection using DriverManager Class\‟s getConnection method:
Connection con = DriverManager.getConnection(\"url,\"myLogin\", \"myPassword\"); //
For example url may be jdbc:odbc:dsn_name.
3. Creating the JDBC Statement: Statement stmt = con.createStatement();
4. Retreiving the data in the ResultSet: ResultSet rs = stmt.executeQuery(query); // where
query can be any valid sql query.

What is the difference between Process and Threads?
Ans: Process is a program in execution. The execution of processes must be sequential.
On the other hand thread is a light-weighted process which is executed in parallel with
other threads. The theard shares some of the resources with other threads but ceratin
things are unique to as particular thread like process id and program counter.

What is the difference between RMI & Corba?
Ans: The main difference between the two is in RMI a method is invoked executing on a
remote machine while in Corba the whole obejct is returned back to the calling machine.
Moreover for RMI object whose method is being called must be alive where as for Corba
object may not need to be alived.

How will you initialize an Applet?
Ans: Using init() method.

What is the order of method invocation in an Applet?
Ans: The following is order:
1. init()


                                                                                          48
2. start()
3. paint()
4. stop()
5. destroy()

When is update method called?
Ans: update method is called every time whenever we call a repaint() method.

How will you pass values from HTML page to the Servlet?
Ans: HTML page calls Servlet using action attribute of form tag. In the servlet
paramaters names and their values can be retreived using
request.getParameterNames() and request.getParameterValues(paramName) functions.

Java Swing interview questions

1) Can a class be it‟s own event handler? Explain how to implement this.

Answer: Sure. an example could be a class that extends Jbutton and implements
ActionListener. In the actionPerformed method, put the code to perform when the button
is pressed.

2) Why does JComponent have add() and remove() methods but Component does
not?

Answer: because JComponent is a subclass of Container, and can contain other
components and jcomponents.

3) How would you create a button with rounded edges?

Answer: there‟s 2 ways. The first thing is to know that a JButton‟s edges are drawn by a
Border. so you can override the Button‟s paintComponent(Graphics) method and draw a
circle or rounded rectangle (whatever), and turn off the border. Or you can create a
custom border that draws a circle or rounded rectangle around any component and set the
button‟s border to it.

4) If I wanted to use a SolarisUI for just a JTabbedPane, and the Metal UI for
everything else, how would I do that?

Answer: in the UIDefaults table, override the entry for tabbed pane and put in the
SolarisUI delegate. (I don‟t know it offhand, but I think it‟s
"com.sun.ui.motiflookandfeel.MotifTabbedPaneUI" - anything simiar is a good answer.)

5) What is the difference between the „Font‟ and „FontMetrics‟ class?




                                                                                      49
Answer: The Font Class is used to render „glyphs‟ - the characters you see on the screen.
FontMetrics encapsulates information about a specific font on a specific Graphics object.
(width of the characters, ascent, descent)

6) What class is at the top of the AWT event hierarchy?

Answer: java.awt.AWTEvent. if they say java.awt.Event, they haven‟t dealt with swing
or AWT in a while.

7) Explain how to render an HTML page using only Swing.

Answer: Use a JEditorPane or JTextPane and set it with an HTMLEditorKit, then load
the text into the pane.

8) How would you detect a keypress in a JComboBox?

Answer: This is a trick. most people would say „add a KeyListener to the JComboBox‟ -
but the right answer is „add a KeyListener to the JComboBox‟s editor component.‟

9) Why should the implementation of any Swing callback (like a listener) execute
quickly?

A: Because callbacks are invoked by the event dispatch thread which will be blocked
processing other events for as long as your method takes to execute.

10) In what context should the value of Swing components be updated directly?

A: Swing components should be updated directly only in the context of callback methods
invoked from the event dispatch thread. Any other context is not thread safe?

11) Why would you use SwingUtilities.invokeAndWait or
SwingUtilities.invokeLater?

A: I want to update a Swing component but I‟m not in a callback. If I want the update to
happen immediately (perhaps for a progress bar component) then I‟d use invokeAndWait.
If I don‟t care when the update occurs, I‟d use invokeLater.

12) If your UI seems to freeze periodically, what might be a likely reason?

A: A callback implementation like ActionListener.actionPerformed or
MouseListener.mouseClicked is taking a long time to execute thereby blocking the event
dispatch thread from processing other UI events.

13) Which Swing methods are thread-safe?

A: The only thread-safe methods are repaint(), revalidate(), and invalidate()


                                                                                       50
14) Why won‟t the JVM terminate when I close all the application windows?

A: The AWT event dispatcher thread is not a daemon thread. You must explicitly call
System.exit to terminate the JVM.

Java interview questions

Q1: What are the advantages of OOPL?

Ans: Object oriented programming languages directly represent the real life objects. The
features of OOPL as inhreitance, polymorphism, encapsulation makes it powerful.

Q2: What do mean by polymorphisum, inheritance, encapsulation?

Ans: Polymorhisum: is a feature of OOPl that at run time depending upon the type of
object the appropriate method is called.
Inheritance: is a feature of OOPL that represents the "is a" relationship between different
objects(classes). Say in real life a manager is a employee. So in OOPL manger class is
inherited from the employee class.
Encapsulation: is a feature of OOPL that is used to hide the information.

Q3: What do you mean by static methods?

Ans: By using the static method there is no need creating an object of that class to use
that method. We can directly call that method on that class. For example, say class A has
static function f(), then we can call f() function as A.f(). There is no need of creating an
object of class A.

Q4: What do you mean by virtual methods?

Ans: virtual methods are used to use the polymorhism feature in C++. Say class A is
inherited from class B. If we declare say fuction f() as virtual in class B and override the
same function in class A then at runtime appropriate method of the class will be called
depending upon the type of the object.

Q5: Given two tables Student(SID, Name, Course) and Level(SID, level) write the
SQL statement to get the name and SID of the student who are taking course = 3
and at freshman level.

Ans: SELECT Student.name, Student.SID
FROM Student, Level
WHERE Student.SID = Level.SID
AND Level.Level = "freshman"
AND Student.Course = 3;

Q6: What are the disadvantages of using threads?


                                                                                           51
Ans: DeadLock.

Q1: Write the Java code to declare any constant (say gravitational constant) and to
get its value

Ans: Class ABC
{
static final float GRAVITATIONAL_CONSTANT = 9.8;
public void getConstant()
{
system.out.println("Gravitational_Constant: " + GRAVITATIONAL_CONSTANT);
}
}
Q2: What do you mean by multiple inheritance in C++ ?

Ans: Multiple inheritance is a feature in C++ by which one class can be of different
types. Say class teachingAssistant is inherited from two classes say teacher and Student.

Q3: Can you write Java code for declaration of multiple inheritance in Java ?

Ans: Class C extends A implements B
{
}

Java software engineering interview questions

Question 1: What is the three tier model?
Answer: It is the presentation, logic, backend
Question 2: Why do we have index table in the database?
Answer: Because the index table contain the information of the other tables. It will
be faster if we access the index table to find out what the other contain.
Question 3: Give an example of using JDBC access the database.
Answer:
try
{
Class.forName("register the driver");
Connection con = DriverManager.getConnection("url of db", "username","password");
Statement state = con.createStatement();
state.executeUpdate("create table testing(firstname varchar(20), lastname varchar(20))");
state.executeQuery("insert into testing values(‟phu‟,'huynh‟)");
state.close();
con.close();
}
catch(Exception e)
{
System.out.println(e);


                                                                                        52
}
Question 4: What is the different of an Applet and a Java Application
Answer: The applet doesn‟t have the main function
Question 5: How do we pass a reference parameter to a function in Java?
Answer: Even though Java doesn‟t accept reference parameter, but we can
pass in the object for the parameter of the function.
For example in C++, we can do this:

void changeValue(int& a)
{
a++;
}
void main()
{
int b=2;
changeValue(b);
}

however in Java, we cannot do the same thing. So we can pass the
the int value into Integer object, and we pass this object into the
the function. And this function will change the object.

JSP interview questions

Q: What are the most common techniques for reusing functionality in object-
oriented systems?
A: The two most common techniques for reusing functionality in object-oriented systems
are class inheritance and object composition.

Class inheritance lets you define the implementation of one class in terms of another‟s.
Reuse by subclassing is often referred to as white-box reuse.
Object composition is an alternative to class inheritance. Here, new functionality is
obtained by assembling or composing objects to get more complex functionality. This is
known as black-box reuse.

Q: Why would you want to have more than one catch block associated with a single
try block in Java?
A: Since there are many things can go wrong to a single executed statement, we should
have more than one catch(s) to catch any errors that might occur.

Q: What language is used by a relational model to describe the structure of a
database?
A: The Data Definition Language.

Q: What is JSP? Describe its concept.
A: JSP is the JavaServer Page. The JavaServer Page concept is to provide an HTML


                                                                                       53
document with the ability to plug in content at selected locations in the document. (This
content is then supplied by the Web server along with the rest of the HTML document at
the time the document is downloaded).

Q: What does the JSP engine do when presented with a JavaServer Page to process?
A: The JSP engine builds a servlet. The HTML portions of the JavaServer Page become
Strings transmitted to print methods of a PrintWriter object. The JSP tag portions result in
calls to methods of the appropriate JavaBean class whose output is translated into more
calls to a println method to place the result in the HTML document.

Java and networking interview questions

QUESTION: What is a JavaBean? (asked by Lifescan inc)

ANSWER: JavaBeans are reusable software components written in the Java
programming language, designed to be manipulated visually by a software develpoment
environment, like JBuilder or VisualAge for Java. They are similar to Microsoft‟s
ActiveX components, but designed to be platform-neutral, running anywhere there is a
Java Virtual Machine (JVM).

QUESTION: What are the seven layers(OSI model) of networking? (asked by
Caspio.com)

ANSWER: 1.Physical, 2.Data Link, 3.Network, 4.Transport, 5.Session, 6.Presentation
and 7.Application Layers.

QUESTION: What are some advantages and disadvantages of Java Sockets? (asked
by Arashsoft.com)

ANSWER:
Advantages of Java Sockets:

Sockets are flexible and sufficient. Efficient socket based programming can be easily
implemented for general communications.

Sockets cause low network traffic. Unlike HTML forms and CGI scripts that generate
and transfer whole web pages for each new request, Java applets can send only necessary
updated information.

Disadvantages of Java Sockets:

Security restrictions are sometimes overbearing because a Java applet running in a Web
browser is only able to establish connections to the machine where it came from, and to
nowhere else on the network




                                                                                         54
Despite all of the useful and helpful Java features, Socket based communications allows
only to send packets of raw data between applications. Both the client-side and server-
side have to provide mechanisms to make the data useful in any way.

Since the data formats and protocols remain application specific, the re-use of socket
based implementations is limited.

QUESTION: What is the difference between a NULL pointer and a void pointer?
(asked by Lifescan inc)

ANSWER: A NULL pointer is a pointer of any type whose value is zero. A void pointer
is a pointer to an object of an unknown type, and is guaranteed to have enough bits to
hold a pointer to any object. A void pointer is not guaranteed to have enough bits to point
to a function (though in general practice it does).

QUESTION: What is encapsulation technique? (asked by Microsoft)

ANSWER: Hiding data within the class and making it available only through the
methods. This technique is used to protect your class against accidental changes to fields,
which might leave the class in an inconsistent state.

Advanced enterprise Java interview questions

1) What is the purpose of garbage collection in Java, and when is it used?

The purpose of garbage collection is to identify and discard objects that are no longer
needed by a program so that their resources can be reclaimed and reused. A Java object is
subject to garbage collection when it becomes unreachable to the program in which it is
used.

2) Describe synchronization in respect to multithreading.

With respect to multithreading, synchronization is the capability to control the access of
multiple threads to shared resources. Without synchonization, it is possible for one thread
to modify a shared variable while another thread is in the process of using or updating
same shared variable. This usually leads to significant errors.

>

3) How is JavaBeans differ from Enterprise JavaBeans?

The JavaBeans architecture is meant to provide a format for general-purpose components.
On the other hand, the Enterprise JavaBeans architecture provides a format for highly
specialized business logic components.

4) In what ways do design patterns help build better software?


                                                                                         55
Design patterns helps software developers to reuse successful designs and architectures.
It helps them to choose design alternatives that make a system reusuable and avoid
alternatives that compromise reusability through proven techniques as design patterns.

5) Describe 3-Tier Architecture in enterprise application development.

In 3-tier architecture, an application is broken up into 3 separate logical layers, each with
a well-defined set of interfaces. The presentation layer typically consists of a graphical
user interfaces. The business layer consists of the application or business logic, and the
data layer contains the data that is needed for the application.

Advanced Java interview questions

Q:In Java, what is the difference between an Interface and an Abstract class?

A: An Abstract class declares have at least one instance method that is declared abstract
which will be implemented by the subclasses. An abstract class can have instance
methods that implement a default behavior. An Interface can only declare constants and
instance methods, but cannot implement default behavior.

Q: Can you have virtual functions in Java? Yes or No. If yes, then what are virtual
functions?

A: Yes, Java class functions are virtual by default. Virtual functions are functions of
subclasses that can be invoked from a reference to their superclass. In other words, the
functions of the actual object are called when a function is invoked on the reference to
that object.

Q:Write a function to reverse a linked list p in C++?

A:

Link* reverse_list(Link* p)
{
if (p == NULL)
return NULL;

Link* h = p;
p = p->next;
h->next = NULL;
while (p != null)
{
Link* t = p->next;
p->next = h;
h = p;



                                                                                           56
p = t;
}

return h;
}

Q:In C++, what is the usefulness of Virtual destructors?

A:Virtual destructors are neccessary to reclaim memory that were allocated for objects in
the class hierarchy. If a pointer to a base class object is deleted, then the compiler
guarantees the various subclass destructors are called in reverse order of the object
construction chain.

Q:What are mutex and semaphore? What is the difference between them?

A:A mutex is a synchronization object that allows only one process or thread to access a
critical code block. A semaphore on the other hand allows one or more processes or
threads to access a critial code block. A semaphore is a multiple mutex.

Java Web programming interview questions

Question1:

What is a Servlet?

Answer: Servlets are modules of Java code that run in a server application (hence the
name "Servlets", similar to "Applets" on the client side) to answer client requests.

Question2:

What advantages does CMOS have over TTL(transitor transitor logic)?
(ALCATEL)

Answer:

        low power dissipation
        pulls up to rail
        easy to interface

How is Java unlike C++? (Asked by Sun)

Answer:

Some language features of C++ have been removed. String manipulations in Java do not
allow for buffer overflows and other typical attacks. OS-specific calls are not advised, but



                                                                                         57
you can still call native methods. Everything is a class in Java. Everything is compiled to
Java bytecode, not executable (although that is possible with compiler tools).

Question4:

What is HTML (Hypertext Markup Language)?

Answer:

HTML (HyperText Markup Language) is the set of "markup" symbols or tags inserted in
a file intended for display on a World Wide Web browser. The markup tells the Web
browser how to display a Web page‟s words and images for the user.

Question5:

Define class.

Answer: A class describes a set of properties (primitives and objects) and behaviors
(methods).

Basic Java interview questions

1. Why do you prefer Java?

Answer: write once ,run anywhere.

2. Name some of the classes which provide the functionality of collation?

Answer: collator, rulebased collator, collationkey, collationelement iterator.

3. Awt stands for? and what is it?

Answer: AWT stands for Abstract window tool kit. It is a is a package that provides an
integrated set of classes to manage user interface components.

4. why a java program can not directly communicate with an ODBC driver?

Answer: Since ODBC API is written in C language and makes use of pointers which Java
can not support.

5. Are servlets platform independent? If so Why? Also what is the most common
application of servlets?

Answer: Yes, Because they are written in Java. The most common application of servlet
is to access database and dynamically construct HTTP response



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