about packages by urssravan

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									Packages
•A package is a collection of related classes and interfaces that
 provides access protection and namespace management.
•Packages are created using the package keyword.
Example:
package graphics;




                         TCS Internal
Packages
•Classes belong to one package are stored in the subdirectory
 whose name is same as the package name.
•Package member can be accessed by using import keyword.
•Only public members of package are accessible to universe.




                        TCS Internal
Java Class Path
•When the Java compiler encounters a new class, it must be
 able to find that class in order to resolve names, do type
 checking etc.
•When the Java interpreter encounters a new class, it must be
 able to find the class to load it and invoke its methods, etc.




                         TCS Internal
Access Specifiers
•Java provides four distinct access specifiers for class
 members.
  – private
  – protected
  – public
  – default / (package wide scope)




                          TCS Internal
Various locations of classes
•The class itself
•Its sub class in the same package
•Other classes in the same package
•Its sub class in a different package
•Other classes in other packages.




                         TCS Internal
Java Class Path
•Both compiler and interpreter search for classes in the
 specified directory.
•The directory specification is provided by CLASSPATH
 environment variable.
•A class path is a list of directories or zip files to search for the
 class files.
•The classpath can also be passed explicitly to javac or java




                           TCS Internal
Access Control
                    Private                  Default   Protected   Public


Class
                                                                 

Sub class, same
                                                                 
package
Other class, same
package                                                          

Sub class, diff
package                                                          

Other class, diff
package                                                          




                              TCS Internal
Java Language Library
•Defined in “java.lang” package.
•By default available for all Java programs and no need to
 import it explicitly.
•It contains classes and interfaces that are fundamental to
 virtually all classes.




                         TCS Internal
java.lang Package
•Wrapper classes                       •Process
  – Boolean, Integer, Float            •Runtime
     etc.                              •System
•String                                •Thread
•Class
•ClassLoader
•Object




                        TCS Internal
java.lang Package
•Interface
   – Clonable
   – Comparable
   – Runnable




                    TCS Internal
Java.util Package

•StringTokenizer                            •Calendar
  – To parse strings                           – Calendar related utilities
•BitSet                                     •TimeZone
  – To store an array of                       – The time zone of various
     bits                                        places
•Date
                                            •Random
  – Date related utilities
                                               – To generate Random number



                             TCS Internal
Java.util Package
• Collection Framework
    – ArrayList
    – LinkedList
    – HashSet
    – TreeSet
    – HashMap
    – TreeMap
• Legacy Classes
    – Vector
    – Hashtable
    – Stack
    – Properties



                         TCS Internal
Java.io Package
•Streams
  – Byte Streams
  – Character Streams
•Abstract classes
  – Byte
     •InputStream
     •OutputStream
  – Character
     •Reader
     •Writer
                        TCS Internal
Java.io Package
•Abstract Methods
  read()
  write()




                    TCS Internal
java.io Package

•Some Classes for byte streams
  – FileInputStream / FileOutputStream
  – ByteArrayInputStream/ByteArrayOutputStream
  – FilterOutputStream/FilterInputStream
  – BufferedInputStream/BufferedOutputStream
  – ObjectInputStream / ObjectOutputStream




                     TCS Internal
java.io Package

•Some Classes for character streams
  – FileReader / FileWriter
  – CharArrayReader / CharArrayWriter
  – BufferedReader / BufferedWriter
  – PushbackReader / PushbackWriter
  – PrintWriter




                      TCS Internal
Some Other Libraries
•java.net.*           - network related
•java.sql.*           - database related
•java.awt.*           - GUI related
•javax.swing.*        - Advanced GUI
•java.applet.*        - Applet Related
•java.security.*      - Security related

 And a lot more libraries are available for ready use.




                          TCS Internal
Using Java Documentation
   All
 Package
    s




            Classes &
           Interfaces in                    Class
            a Package                     Description




                           TCS Internal
Summary
•In this session, you learned:
   – Packages
   – Access Control
   – Java Language Library
   – Java Utility Library
   – Java I/O Library
   – Other Java Libraries
   – Using Java API documentation



                       TCS Internal

								
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