Docstoc

C# and Dot Net Interview

Document Sample
C# and Dot Net Interview Powered By Docstoc
					Where does the version dependencies recorded Inside an assembly‘s manifest

How do you refer parent classes in C# This keyword is used for reffering current object and Base keyword is used for referring parrent class. so ans. is C

Which attribute you generally find on top of main method [ STAThread ]

How do you make a class not instantiable Making class as Abstract

In a multilevel hierarchy how are the constructors are called TopDown Always a parent class constructor is executed before child class‘ constructor does .. when u instantiate a child/derived class.

Which utility is used to create resource file resgen

What is the extension of a resource file .resx

A shared assembly must have a strong name to uniquely identify the assembly True

Public policy applies to Public policies are applied on Shared Assemblies.

Stream object can not be initialized True

Which of the following has stream as the base class BufferedStream,MemoryStream and FileStream all these 3 classes are inherited from System.IO.Stream class. What is the use of fixed statement The fixed statement sets a pointer to a managed variable and ―pins‖ that variable during the execution of statement. Without fixed, pointers to managed variables would be of little use since garbage collection could relocate the variables unpredictably. (In fact, the C# compiler will not allow you to set a pointer to a managed variable except in a fixed statement.) Eg: Class A { public int i; } A objA = new A; // A is a .net managed type fixed(int *pt = &objA.i) // use fixed while using pointers with managed // variables { *pt=45; // in this block use the pointer the way u want }

What is the order of destructors called in a polymorphism hierarchy Destructors are called in reverse order of constructors. First destructor of most derived class is called followed by its parent‘s destructor and so on till the topmost class in the hierarchy. You don‘t have control over when the first destructor will be called, since it is determined by the garbage collector. Sometime after the object goes out of scope GC calls the destructor, then its parent‘s destructor and so on.

When a program terminates definitely all object‘s destructors are called.

How can you sort the elements of the array in descending order int[] arr = new int[3]; arr[0] = 4; arr[1] = 1; arr[2] = 5; Array.Sort(arr); Array.Reverse(arr);

Is it possible to Override Private Virtual methods No: First of all you cannot declare a method as ‗private virtual‘.

What does the volatile modifier do The system always reads the current value of a volatile object at the point it is requested, even if the previous instruction asked for a value from the same object. Also, the value of the object is written immediately on assignment. The volatile modifier is usually used for a field that is accessed by multiple threads without using the lock statement to serialize access. Using the volatile modifier ensures that one thread retrieves the most up-to-date value written by another thread.

What is the C# equivalent of System.Single Float 32 bit e.g. float i = 6.8F; // or 6.8f By default, a real numeric literal on the right-hand side of the assignment operator is treated as double. Therefore, to initialize a float variable use the suffix f or F. If you don‘t use the suffix in the previous declaration, you will get a compilation error because you are attempting to store a double value into a float variable.

A single line comments are implemented by //

Code running under the control of CLR is often referred as Managed Code

Platform specific code is obtained when MSIL code is the intermediate code which is platform independent. When MSIL is compiled actual platform dependent code is generated.

Intermediate Language also facilitates language interoperability True

NET interfaces are not derived from IUnknown & they do not have associated GUID’s True

Code written in C# can not used in which of the languages Java

It is not possible to debug the classes written in other .Net languages in a C# project. False: It is definitely possible to debug other .Net languages code in a C# project. As everyone knows .net can come Which class use to Read/Write data to memory MemoryStream It is a nonbuffered stream whose encapsulated data is directly accessible in memory(RAM not files on disk).

To Configure .Net for JIT activation what do you do Actually JIT activation is required for COM+ components which can be done by setting JustInTimeActivation attribute to true (choice A). For .net applications / components JIT comes in by default.

Which method is used by COM+ to ascertain whether class can be pooled CanBePooled

How do you import Activex component in to .NET An application called AXImp.exe shipped with .Net SDK is used. This application does something similar as Tlbimp.exe does for non graphical COM components. It creates a wrapper component that contains the type information that the .Net runtime can understand.

Net Remoting doesn’t allow creating stateless & stateful Remote objects False

Windows services created by C# app run only Windows NT & Above

What is an indexer in C# Indexer is a special syntax for overloading [] operator for a class. After defining an indexer, array syntaxes can be used for the class objects.

In the following cases which is not function overloading Same parameter types but different return values. Function overloading depends on the 1) parameter types

2) number of parameters 3) order of parameters

How to implement multiple inheritence in C# Multiple inheritence in C# is achived by using Interfaces.

In C# a technique used to stream the data is known as Serialization

Can static methods be overridable? No Which method is actually called ultimately when Console.WriteLine( ) is invoked AppendFormat() method is called.

What happens when you create an arraylist as ArrayList Arr=new ArrayList() Once it will reach size 16 addding element in the arraylist, it will be automatically double the size.

What is the output of Vectors.RemoveAt(1) Removes the object at position 1

GetEnumerator( ) of Ienumerable interface returns GetEnumerator() returns a reference to System.Collections.Ienumerator class which allows a simple iteration over a collection

How do you add objects to hashtable Actually operator ―=‖ adds an element too.

The following example adds key-value pair ―x‖-‖value‖ to Hashatble h: HashTable h = new HashTable(); h(‖x‖) = ―value‖;

If A.equals(B) is true then A.getHashcode & B.getHashCode must always return same hash code The answer is False because it is given that A.equals(B) returns true i.e. objects are equal and now its hashCode is asked which is always independent of the fact that whether objects are equal or not. So, GetHashCode for both of the objects returns different value. Ans: False

The assembly class is defined in System.Reflection

What is the first step to do anything with assembly Load assembly to running process

How do you load assembly to running process Assembly class provides the following methods to load an assembly: Load LoadFrom LoadFile LoadWithPartialName LoadModule

Assemblies cannot be loaded side by side

This is possible in .net and thats the way DLL hell is said to be eliminated, its clearly evident from the GAC

Application Isolation is assured using ApplicationDomain Which method is implicitly called when an object is created When an object is created Constructor is get called first. A default constructor is created automatically if we do not create a constructor inside a class.

Which of the following statement is invalid with regards to constructor Constructors should have the same name as class name Constructors have to be public so that class can be instantiated Constructors can not be overloaded

Constructors can not be static C# supports two types of constructor, a class constructor (static constructor) and an instance constructor (non-static constructor). Static constructor is used to initialize static data members as soon as the class is referenced first time, whereas an instance constructor is used to create an instance of that class with <new> keyword. A static constructor does not take access modifiers or have parameters and can‘t access any non-static data member of a class. Since static constructor is a class constructor, they are guaranteed to be called as soon as we refer to that class or by creating an instance of that class.

It is not possible for a delegate to wrap more than 1 methods False In some cases you may want to call not just one, but two or more methods through a single delegate. This is known as multicasting. You accomplish multicasting by encapsulating the various methods in delegates, and then you combine the delegates using the Delegate.Combine shared method. The Combine method takes an array of delegates as a parameter and returns a new delegate that represents the combination of all the delegates in the array.

In C# events are actually a special form of delegates False Events are signals generated by an object to indicate occurrence of an action, while delegates are type safe function pointers. An event is a way for a class to signal state change / an interesting action. Delegates are reference types which are used to encapsulate methods with a specific signature. Events are declared using delegates. Objects which want to take some action on occurrence of the event attach their methods to the event handler, which is a delegate.

Which preprocessor directive are used to mark that contain block of code is to be treated as a single block #Region and #EndRegion indicates a block of code which can be expanded / collapsed.

How are the attributes specified in C# They are enclosed with in [].

For performing repeated modification on string which class is preferred? StringBuilder class is preferred for performing repeated operations on string since its value is mutable. String class represents a text value which is immutable. All operations on string class which appear to be modifying its value actually return the new value. So for modifying text contents StringBuilder class is preferred.

In order to use stringbuilder in our class we need to refer We only need to refer System.Text namespace. StringBuilder Class is contained in the System.Text namespace. hence we need to add the following lines in pur code: using System.Text;

Which of the following is not a member of stringbuilder Answer is: Dsubstring(); What is XML Schema? Document Type Declaration(DTD) <!DOCTYPE root-element [ doctype-declaration… ]> determines the name of the root element and contains the document type declarations Elements Elements are the main building blocks of both XML and HTML documents. Examples of HTML elements are ―body‖ and ―table‖. Examples of XML elements could be ―note‖ and ―message‖. Elements can contain text, other elements, or be empty. Examples of empty HTML elements are ―hr‖, ―br‖ and ―img‖. Examples: <body>body text in between</body> <message>some message in between</message> ———– Attributes Attributes provide extra information about elements. Attributes are always placed inside the starting tag of an element. Attributes always come in name/value pairs. The following ―img‖ element has additional information about a source file: <img src=‖computer.gif‖ /> The name of the element is ―img‖. The name of the attribute is ―src‖. The value of the attribute is ―computer.gif‖. Since the element itself is empty it is closed by a ‖ /‖. ———– Entities Entities are variables used to define common text. Entity references are references to entities. Most of you will know the HTML entity reference: ‖ ―. This ―no-breaking-space‖ entity is used in HTML to insert an extra space in a document. Entities are expanded when a document is parsed by an XML parser. The following entities are predefined in XML:

Entity References Character << >> && ‖― ‗‗

How can i check whether a dataset is empty or not in C#.net HasRows property is only for DataReader objects. For DataSet you can check whether it has a DataTable or not .. since the DataSet is a collection of DataTable you can check whether it has loaded a table or not using the following code DataSet dt=new DataSet(); if (dt.Tables.Count>0) // has tables in it { } else // otherwise it is empty { }

Is it possible to inherit a class that has only private constructor? No. ex. Base Class: /// Summary description for BaseA. /// </summary> public class BaseA

{ private BaseA() { // // TODO: Add constructor logic here // } } Dervied Class: /// <summary> /// Summary description for Class1. /// </summary> public class DerviedB: BaseA { public DerviedB() { // // TODO: Add constructor logic here // } } Result: DerviedB.cs(10): ‗PrivateAssembly.BaseA.BaseA()‘ is inaccessible due to its protection level

How do you choose 1 entry point when C# project has more Main( ) method?

In one .cs file there may be many classes having Main() method. While making the .exe you can define the class name as an entry point CSC /main:classname filename.cs

The compiler throws an error if XML comments is not well formed If the XML is not well-formed, a warning is generated and the documentation file will contain a comment saying that an error was encountered.

By declaring a base class function as virtual we allow the function to be overridden in subclasses The derived class can provide new functionality by overriding the virtual method of the base class. The method to be called is determined at the run-time depending on the type of the object calling the method, and it does not depend on the type of the variable declared to hold the object. The following example illustrates this point: Suppose base class B and derived class D provide different implementations of a virtual method V(). Also suppose that there is a non-virtual method NV() of B which is overriden by D. //In Main(), an object, obj, is declared to be of type B. B obj; //An object of D is created for initializing obj obj = new D; //Call virtual and non-virtual methods on obj: obj.V(); //This call would execute D::F() since F() is virtual, and although obj is declared to be of type B, it contains object of type D. obj.NV(); //This call would execute B::F(), looking at the declaration of obj. This is the difference between virtual and plain overridable methods. Virtual methods execute slower than non-virtual ones because of run-time resolve of the method to be called. So programmer should be caeful while declaring a method as virtual.

Which of the following can not be declared as virtual Both A and B are correct choices. Declaring a static function as virtual generates build error. Same with declaring member fields as virtual.

A static function can be called only using class_name.static_function_name() syntax, so there is no run-time resolve depending on the type of object, hence the term virtual does not make a sense in case of static functions. In case member fields are overriden by a derived class the derived class methods will use the overriden variables by default, so there is no run-time resolve required for fields.

Sealed class can be inherited sealed classes cannot be inherited as the sealed classes provides full functionality only the classes that have no full functionality can be inherited

Which of the following statements is not true for interfaces Interfaces must always be declared as public so that they can be implemented or inherited

It is not permitted to declare modifier on the members in an interface definition A is the correct answer. By default all the members in an Interface definition are public, so there is no need to declare access modifier public. It would be a compile time error otherwise

Interface members can not be declared as Virtual keyword is meaningful when the derived class is expected to override base class method. Here a class will ‗implement‘ a method of an interface, hence virtual is not meaningful for interface methods. Static keyword indicates that a method or field is common to all instances of a class. For an interface there will not be any instance, hence static is not meaningful. An interface and all its methods must be declared public for enabling classes to implement them. How to find exceptions in database If program successfully complie . but program is not run or execute.then give an exception.

How can objects be late bound in .NET?

Instead of using new keyword we can use create object like in this example we are creating object to write in excel sheet through our programexampleImports Excel = Microsoft.Office.Interop.ExcelPrivate Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim objApp As Object Dim objBook As Object Dim objBooks As Object Dim objSheets As Object Dim objSheet As Object Dim range As Object ‗ Instantiate Excel and start a new workbook. objApp = CreateObject(‖Excel.Application‖) objBooks = objApp.Workbooks objBook = objBooks.Add objSheets = objBook.Worksheets objSheet = objSheets.Item(1) range = objSheet.Range(‖A1″) ‗Set the range value. range.Value = ―Hello, World!‖ ‗Return control of Excel to the user. objApp.Visible = True objApp.UserControl = TrueEnd Sub

Where we can use DLL made in C#.Net Supporting .Net, bcoz DLL made in C#.Net semicompiled version. Its not a com object. It is used only in .Net Framework.As it is to be compiled at runtime to byte code.

What Datatypes does the RangeValidator Control support? String, Integer, Double, Date, Currency

Constructor is the method which is implicitly created when ever a class is instantiated. Why? Constructors are class methods that are executed when an object of a given type is created. Constructors have the same name as the class, and usually initialize the data members of the new object

Why multiple Inheritance is not possible in C#? Multiple Inheritance is possible in C++, but its not possible in Java, and C#. what we are read above those are all we know, but as per my knowledge, in C++ to resolve multiple inheritance we are using ―this pointer‖. But in C# there is no pointer concept. In such way, the architectures using the interface concept. To resolving the ambiguity ―this pointer‖ concept used in c++. Offcourse it not absolutely correct, but its my idea only. If you are agree with my view then follow it, else leave it.

Why strings are immutable? 1) In VB6.0 and c++ strings are simple array of bytes, but in .Net it is class System.String and is immutable.

2) A string is a sequential collection of Unicode characters, which usually is used to represent text. A String, on the other hand, is a .NET Framework class (System.String) that represents a Unicode string with a sequential collection of System.Char structure.

How to convert ocx into DLL you cannot convert OCX to dll becoz dll do not have GUI interfaces .IF your ocx does not have GUI and you have convert manuly by cut and paste from OCX to Dll project

What is the main difference between pointer and delegate with examples? A Delegate in c# allows to pass a method of class to object of other class. Rules in Deligation:1.In order to create a Delegate a Signature(parameter) must match Signature of object. 2.Define all the methods which has the same Signature as Deligate define. 3.Create the deligate object & pass the method as a parameter to Deligate. 4.Now call the encapsulated method using deligated object. the best example of Deligation modle is ADO.NET Architecture & Event Handling in windows environament.

How do i read the information from web.config file? string ConStrFromWeb=System.Configuration.ConfigurationSettings.AppSettings[‖ConStringKey‖]; // Here ConStringKey is the key name of connection string in web.config

What is the default Function arguments? Default function argument is a function argument with a default value. Callers of this function have a choice whether to pass a value for default argument or not. If a function call passes a value for default argument it is used as its value. If a function call does not pass a value the default value specified in the function definition is used. A function may have any number of default arguments. However all these arguments must follow all mandatory arguments. That is first you have to specify all non-default or mandatory parameters and then all default parameters.

What is the difference between shadow and override? Overriding is used to redefines only the methods.but shadowing redefines the entire element.

You have an event handler called MyEvent and you want to link the click event of control, MyButton, to use MyEvent, what is the code that will like them together? control.Click += new EventHandler(MyEvent)

Which debugging window allows you to see the methods called in the order they were called? The call stack.

Which debugging window allows you to see all the name and values of all the variables in scope? In Call stack window in MS Visual Studio IDE.

What is wrapper class?is it available in c#? Wrapper Classes are the classes that wrap up the primitive values in to a class that offer utility method to access it . For eg you can store list of int values in a vector class and access the class. Also the methods are static and hence you can use them without creating an instance . The values are immutable .

What is protected internal class in C# Class can be internal not protected or not even protected internal. Class can have only two access modifiers Public and internal.if any field or method having access modifier protected internal then this field available to the others assemblies class and as well as class whose inharits this class.

Which keyword is used of specify a class that cannot inherit by other class By using ―sealed‖ keyword we can restrict a class from inheritence.

Can u create the instance for abstract classes

No we cannot instanciate abstract class we hav to extend it first exabstract class A {} class B : A {} Class C { B b=new B; }

Can we use Friend Classes or functions in C# the way we use it in C++ No we can not use friend keyword but instead c# provide ―internal‖ keyword for friend

How we can use inheritance and polymorphisms in c# programming? Inheritance in C# is similar to cpp, if you are familiar to cpp, the only difference is you dont inherit a class in public or protected mode, the way to inherit a class is Class Base { protected int length, breadth; public Base(int a, int b) { this.length = a; this.breadth = b; } public virtual int Show() { Console.WriteLine(Length of a rectangle is {0} and breadth is {1}, length, breadth); } } Class Derived: Base // The way to inherit a class in C# { public Derived(int l, int b, string color): base(l, b) // call Base constructor { this.color = color; } // an overridden method beacuse in the derived method we can // change the behaviour, This is a kind on polymorphism. public override int Show() { base.Show(); Console.WriteLine(‖Color of the rectangle is ‖ color); } public string color; } Class Tester { public static void Main() { Base b = new Base(10, 20); Derived d = new Derived(30, 40, ―Red‖ ); b.Show(); d.show(); } }Output: Length of a rectangle is 10 and breadth is 20 Length of a rectangle is 30 and breadth is 40 Color of the rectangle is RedI hope this will make you a bit clear about Inheritance and polymorphism.

1. Does C# support multiple-inheritance? No. 2. Who is a protected class-level variable available to? It is available to any sub-class (a class inheriting this class). 3. Are private class-level variables inherited? Yes, but they are not accessible. Although they are not visible or accessible via the class interface, they are inherited.

4. Describe the accessibility modifier “protected internal”. It is available to classes that are within the same assembly and derived from the specified base class. 5. What‟s the top .NET class that everything is derived from? System.Object. 6. What does the term immutable mean? The data value may not be changed. Note: The variable value may be changed, but the original immutable data value was discarded and a new data value was created in memory. 7. What‟s the difference between System.String and System.Text.StringBuilder classes? System.String is immutable. System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed. 8. What‟s the advantage of using System.Text.StringBuilder over System.String? StringBuilder is more efficient in cases where there is a large amount of string manipulation. Strings are immutable, so each time a string is changed, a new instance in memory is created. 9. Can you store multiple data types in System.Array? No. 10. What‟s the difference between the System.Array.CopyTo() and System.Array.Clone()? The Clone() method returns a new array (a shallow copy) object containing all the elements in the original array. The CopyTo() method copies the elements into another existing array. Both perform a shallow copy. A shallow copy means the contents (each array element) contains references to the same object as the elements in the original array. A deep copy (which neither of these methods performs) would create a new instance of each element‟s object, resulting in a different, yet identacle object. 11. How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods. 12. What‟s the .NET collection class that allows an element to be accessed using a unique key? HashTable. 13. What class is underneath the SortedList class? A sorted HashTable. 14. Will the finally block get executed if an exception has not occurred? Yes. 15. What‟s the C# syntax to catch any possible exception? A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}. 16. Can multiple catch blocks be executed for a single try statement? No. Once the proper catch block processed, control is transferred to the finally block (if there are any).

17. Explain the three services model commonly know as a three-tier application. Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources). 18. What is the syntax to inherit from a class in C#? Place a colon and then the name of the base class. Example: class MyNewClass : MyBaseClass 19. Can you prevent your class from being inherited by another class? Yes. The keyword “sealed” will prevent the class from being inherited. 20. Can you allow a class to be inherited, but prevent the method from being over-ridden? Yes. Just leave the class public and make the method sealed. 21. What‟s an abstract class? A class that cannot be instantiated. An abstract class is a class that must be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without any implementation. 22. When do you absolutely have to declare a class as abstract? 1. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden. 2. When at least one of the methods in the class is abstract. 23. What is an interface class? Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes. 24. Why can‟t you specify the accessibility modifier for methods inside the interface? They all must be public, and are therefore public by default. 25. Can you inherit multiple interfaces? Yes. .NET does support multiple interfaces. 26. What happens if you inherit multiple interfaces and they have conflicting method names? It‟s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you‟re okay. To Do: Investigate 27. What‟s the difference between an interface and abstract class? In an interface class, all methods are abstract - there is no implementation. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed. An abstract class may have accessibility modifiers. 28. What is the difference between a Struct and a Class? Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval. Another difference is that structs cannot inherit. 29. Is it possible to inline assembly or IL in C# code? No.

30. Is it possible to have different access modifiers on the get/set methods of a property? No. The access modifier on a property applies to both its get and set accessors. What you need to do if you want them to be different is make the property readonly (by only providing a get accessor) and create a private/internal set method that is separate from the property. 31. Is it possible to have a static indexer in C#? No. Static indexers are not allowed in C#. 32. If I return out of a try/finally in C#, does the code in the finally-clause run? Yes. The code in the finally always runs. If you return out of the try block, or even if you do a “goto” out of the try, the finally block always runs:
33. using System; 34. 35. class main 36. { 37. public static void Main() 38. { 39. try 40. { 41. Console.WriteLine("In Try block"); 42. return; 43. } 44. finally 45. { 46. Console.WriteLine("In Finally block"); 47. } 48. } }

Both “In Try block” and “In Finally block” will be displayed. Whether the return is in the try block or after the try-finally block, performance is not affected either way. The compiler treats it as if the return were outside the try block anyway. If it‟s a return without an expression (as it is above), the IL emitted is identical whether the return is inside or outside of the try. If the return has an expression, there‟s an extra store/load of the value of the expression (since it has to be computed within the try block). 49. I was trying to use an “out int” parameter in one of my functions. How should I declare the variable that I am passing to it? You should declare the variable as an int, but when you pass it in you must specify it as „out‟, like the following: int i; foo(out i); where foo is declared as follows: [return-type] foo(out int o) { } 50. How does one compare strings in C#? In the past, you had to call .ToString() on the strings when using the == or != operators to compare the strings‟ values. That will still work, but the C# compiler now automatically compares the values instead of the references when the == or != operators are used on string types. If you actually do want to compare references, it can be done as follows: if ((object) str1 == (object) str2) { … } Here‟s an example showing how string compares work:
51. using System;

52. public class StringTest 53. { 54. public static void Main(string[] args) 55. { 56. Object nullObj = null; Object realObj = new StringTest(); 57. int i = 10; 58. Console.WriteLine("Null Object is [" + nullObj + "]n" 59. + "Real Object is [" + realObj + "]n" 60. + "i is [" + i + "]n"); 61. // Show string equality operators 62. string str1 = "foo"; 63. string str2 = "bar"; 64. string str3 = "bar"; 65. Console.WriteLine("{0} == {1} ? {2}", str1, str2, str1 == str2 ); 66. Console.WriteLine("{0} == {1} ? {2}", str2, str3, str2 == str3 ); 67. } }

Output:
Null Object is [] Real Object is [StringTest] i is [10] foo == bar ? False bar == bar ? True

68. How do you specify a custom attribute for the entire assembly (rather than for a class)? Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:
69. using System; [assembly : MyAttributeClass] class X {}

Note that in an IDE-created project, by convention, these attributes are placed in AssemblyInfo.cs. 70. How do you mark a method obsolete? [Obsolete] public int Foo() {...}

or
[Obsolete("This is a message describing why this method is obsolete")] public int Foo() {...}

Note: The O in Obsolete is always capitalized. 71. How do you implement thread synchronization (Object.Wait, Notify,and CriticalSection) in C#? You want the lock statement, which is the same as Monitor Enter/Exit:

lock(obj) { // code }

translates to
try { CriticalSection.Enter(obj); // code } finally { CriticalSection.Exit(obj); }

72. How do you directly call a native function exported from a DLL? Here‟s a quick example of the DllImport attribute in action:
73. using System.Runtime.InteropServices; 74. class C 75. { 76. [DllImport("user32.dll")] 77. public static extern int MessageBoxA(int h, string m, string c, int type); 78. public static int Main() 79. { 80. return MessageBoxA(0, "Hello World!", "Caption", 0); 81. } }

This example shows the minimum requirements for declaring a C# method that is implemented in a native DLL. The method C.MessageBoxA() is declared with the static and external modifiers, and has the DllImport attribute, which tells the compiler that the implementation comes from the user32.dll, using the default name of MessageBoxA. For more information, look at the Platform Invoke tutorial in the documentation. 82. How do I simulate optional parameters to COM calls? You must use the Missing class and pass Missing.Value (in System.Reflection) for any values that have optional parameters. 1. Are private class-level variables inherited? Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are. 2. Why does DllImport not work for me? All methods marked with the DllImport attribute must be marked as public static extern. 3. Why does my Windows application pop up a console window every time I run it? Make sure that the target type set in the project properties setting is set to Windows Application, and not Console Application. If you‟re using the command line, compile with /target:winexe, not /target:exe.

4. Why do I get an error (CS1006) when trying to declare a method without specifying a return type? If you leave off the return type on a method declaration, the compiler thinks you are trying to declare a constructor. So if you are trying to declare a method that returns nothing, use void. The following is an example: // This results in a CS1006 error public static staticMethod (mainStatic obj) // This will work as wanted public static void staticMethod (mainStatic obj) 5. Why do I get a syntax error when trying to declare a variable called checked? The word checked is a keyword in C#. 6. Why do I get a security exception when I try to run my C# app? Some security exceptions are thrown if you are working on a network share. There are some parts of the frameworks that will not run if being run off a share (roaming profile, mapped drives, etc.). To see if this is what‟s happening, just move the executable over to your local drive and see if it runs without the exceptions. One of the common exceptions thrown under these conditions is System.Security.SecurityException. To get around this, you can change your security policy for the intranet zone, code group 1.2, (the zone that running off shared folders falls into) by using the caspol.exe tool. 7. Why do I get a CS5001: does not have an entry point defined error when compiling? The most common problem is that you used a lowercase „m‟ when defining the Main method. The correct way to implement the entry point is as follows: class test { static void Main(string[] args) {} } 8. What optimizations does the C# compiler perform when you use the /optimize+ compiler option? The following is a response from a developer on the C# compiler team: We get rid of unused locals (i.e., locals that are never read, even if assigned). We get rid of unreachable code. We get rid of try-catch with an empty try. We get rid of try-finally with an empty try. We get rid of try-finally with an empty finally. We optimize branches over branches: gotoif A, lab1 goto lab2: lab1: turns into: gotoif !A, lab2 lab1: We optimize branches to ret, branches to next instruction, and branches to branches. 9. What is the syntax for calling an overloaded constructor within a constructor (this() and constructorname() does not compile)? The syntax for calling another constructor is as follows: class B { B(int i) { } } class C : B { C() : base(5) // call base constructor B(5) { } C(int i) : this() // call C() { } public static void Main() {} } 10. What is the equivalent to regsvr32 and regsvr32 /u a file in .NET development? Try using RegAsm.exe. Search MSDN on Assembly Registration Tool.

11. What is the difference between a struct and a class in C#? From language spec: The list of similarities between classes and structs is as follows. Longstructs can implement interfaces and can have the same kinds of members as classes. Structs differ from classes in several important ways; however, structs are value types rather than reference types, and inheritance is not supported for structs. Struct values are stored on the stack or in-line. Careful programmers can sometimes enhance performance through judicious use of structs. For example, the use of a struct rather than a class for a Point can make a large difference in the number of memory allocations performed at runtime. The program below creates and initializes an array of 100 points. With Point implemented as a class, 101 separate objects are instantiated-one for the array and one each for the 100 elements. 12. My switch statement works differently than in C++! Why? C# does not support an explicit fall through for case blocks. The following code is not legal and will not compile in C#: switch(x) { case 0: // do something case 1: // do something as continuation of case 0 default: // do something in common with //0, 1 and everything else break; } To achieve the same effect in C#, the code must be modified as shown below (notice how the control flows are explicit): class Test { public static void Main() { int x = 3; switch(x) { case 0: // do something goto case 1; case 1: // do something in common with 0 goto default; default: // do something in common with 0, 1, and anything else break; } } }

13. Is there regular expression (regex) support available to C# developers? Yes. The .NET class libraries provide support for regular expressions. Look at the System.Text.RegularExpressions namespace. 14. Is there any sample C# code for simple threading? Yes: using System; using System.Threading; class ThreadTest { public void runme() { Console.WriteLine(”Runme Called”); } public static void Main(String[] args) { ThreadTest b = new ThreadTest(); Thread t = new Thread(new ThreadStart(b.runme)); t.Start(); } } 15. Is there an equivalent of exit() for quitting a C# .NET application? Yes, you can use System.Environment.Exit(int exitCode) to exit the application or Application.Exit() if it‟s a Windows Forms app. 16. Is there a way to force garbage collection? Yes. Set all references to null and then call System.GC.Collect(). If you need to have some objects destructed, and System.GC.Collect() doesn‟t seem to be doing it for you, you can force finalizers to be run by setting all the references to the object to null and then calling System.GC.RunFinalizers(). 17. Is there a way of specifying which block or loop to break out of when working with nested loops? The easiest way is to use goto: using System; class BreakExample { public static void Main(String[] args) { for(int i=0; i<3; i++) { Console.WriteLine(”Pass {0}: “, i); for( int j=0 ; j<100 ; j++ ) {

if ( j == 10) goto done; Console.WriteLine(”{0} “, j); } Console.WriteLine(”This will not print”); } done: Console.WriteLine(”Loops complete.”); } } 18. Is it possible to restrict the scope of a field/method of a class to the classes in the same namespace? There is no way to restrict to a namespace. Namespaces are never units of protection. But if you‟re using assemblies, you can use the „internal‟ access modifier to restrict access to only within the assembly. 1) The C# keyword „int‟ maps to which .NET type? 1. 2. 3. 4. System.Int16 System.Int32 System.Int64 System.Int128

2) Which of these string definitions will prevent escaping on backslashes in C#? 1. 2. 3. 4. string s = #”n Test string”; string s = “‟n Test string”; string s = @”n Test string”; string s = “n Test string”;

3) Which of these statements correctly declares a two-dimensional array in C#? 1. 2. 3. 4. int[,] myArray; int[][] myArray; int[2] myArray; System.Array[2] myArray;

4) If a method is marked as protected internal who can access it? 1. 2. 3. 4. Classes that are both in the same assembly and derived from the declaring class. Only methods that are in the same class as the method in question. Internal methods can be only be called using reflection. Classes within the same assembly, and classes derived from the declaring class.

5) What is boxing? a) Encapsulating an object in a value type. b) Encapsulating a copy of an object in a value type. c) Encapsulating a value type in an object. d) Encapsulating a copy of a value type in an object. 6) What compiler switch creates an xml file from the xml comments in the files in an assembly? 1. 2. 3. 4. /text /doc /xml /help

7) What is a satellite Assembly? 1. A peripheral assembly designed to monitor permissions requests from an application. 2. Any DLL file used by an EXE file. 3. An assembly containing localized resources for another assembly. 4. An assembly designed to alter the appearance or „skin‟ of an application. What is a delegate? 1. 2. 3. 4. A strongly typed function pointer. A light weight thread or process that can call a single method. A reference to an object in a different process. An inter-process message channel.

9) How does assembly versioning in .NET prevent DLL Hell? 1. The runtime checks to see that only one version of an assembly is on the machine at any one time. 2. .NET allows assemblies to specify the name AND the version of any assemblies they need to run. 3. The compiler offers compile time checking for backward compatibility. 4. It doesn‟t. 10) Which “Gang of Four” design pattern is shown below?
public class A { private A instance;

private A() { } public static A Instance { get { if ( A == null ) A = new A(); return instance; } } }

1. 2. 3. 4.

Factory Abstract Factory Singleton Builder

11) In the NUnit test framework, which attribute must adorn a test class in order for it to be picked up by the NUnit GUI? 1. 2. 3. 4. TestAttribute TestClassAttribute TestFixtureAttribute NUnitTestClassAttribute

12) Which of the following operations can you NOT perform on an ADO.NET DataSet? 1. 2. 3. 4. A DataSet can be synchronised with the database. A DataSet can be synchronised with a RecordSet. A DataSet can be converted to XML. You can infer the schema from a DataSet.

13) In Object Oriented Programming, how would you describe encapsulation? 1. The conversion of one type of object to another. 2. The runtime resolution of method calls. 3. The exposition of data.

4. The separation of interface and implementation. 5. What‟s the advantage of using System.Text.StringBuilder over System.String? StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it‟s being operated on, a new instance is created. 6. Can you store multiple data types in System.Array? No. 7. What‟s the difference between the System.Array.CopyTo() and System.Array.Clone()? The first one performs a deep copy of the array, the second one is shallow. 8. How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods. 9. What‟s the .NET datatype that allows the retrieval of data by a unique key? HashTable. 10. What‟s class SortedList underneath? A sorted HashTable. 11. Will finally block get executed if the exception had not occurred? Yes. 12. What‟s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception? A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}. 13. Can multiple catch blocks be executed? No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block. 14. Why is it a bad idea to throw your own exceptions? Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project. Advanced C# interview questions 1. What‟s the advantage of using System.Text.StringBuilder over System.String? StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it‟s being operated on, a new instance is created. 2. Can you store multiple data types in System.Array? No. 3. What‟s the difference between the System.Array.CopyTo() and System.Array.Clone()? The first one performs a deep copy of the array, the second one is shallow. 4. How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods. 5. What‟s the .NET datatype that allows the retrieval of data by a unique key? HashTable. 6. What‟s class SortedList underneath? A sorted HashTable. 7. Will finally block get executed if the exception had not occurred? Yes. 8. What‟s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception? A catch block that catches the exception of type

System.Exception. You can also omit the parameter data type in this case and just write catch {}. 9. Can multiple catch blocks be executed? No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block. 10. Why is it a bad idea to throw your own exceptions? Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project. 11. What‟s a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers. 12. What‟s a multicast delegate? It‟s a delegate that points to and eventually fires off several methods. 13. How‟s the DLL Hell problem solved in .NET? Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly. 14. What are the ways to deploy an assembly? An MSI installer, a CAB archive, and XCOPY command. 15. What‟s a satellite assembly? When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies. 16. What namespaces are necessary to create a localized application? System.Globalization, System.Resources. 17. What‟s the difference between // comments, /* */ comments and /// comments? Single-line, multi-line and XML documentation comments. 18. How do you generate documentation from the C# file commented properly with a command-line compiler? Compile it with a /doc switch. 19. What‟s the difference between <c> and <code> XML documentation tag? Single line code example and multiple-line code example. 20. Is XML case-sensitive? Yes, so <Student> and <student> are different elements. 21. What debugging tools come with the .NET SDK? CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch. 22. What does the This window show in the debugger? It points to the object that‟s pointed to by this reference. Object‟s instance data is shown. 23. What does assert() do? In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true. 24. What‟s the difference between the Debug class and Trace class? Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds. 25. Why are there five tracing levels in System.Diagnostics.TraceSwitcher? The tracing dumps can be quite verbose and for some applications that are constantly

running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities. 26. Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor. 27. How do you debug an ASP.NET Web application? Attach the aspnet_wp.exe process to the DbgClr debugger. 28. What are three test cases you should go through in unit testing? Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly). 29. Can you change the value of a variable while debugging a C# application? Yes, if you are debugging via Visual Studio.NET, just go to Immediate window. 30. Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources). 31. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET? SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it‟s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines. 32. What‟s the role of the DataReader class in ADO.NET connections? It returns a read-only dataset from the data source when the command is executed. 33. What is the wildcard character in SQL? Let‟s say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve „La%‟. 34. Explain ACID rule of thumb for transactions. Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn‟t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after). 35. What connections does Microsoft SQL Server support? Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords). 36. Which one is trusted and which one is untrusted? Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction. 37. Why would you use untrusted verificaion? Web Services might use it, as well as non-Windows applications. 38. What does the parameter Initial Catalog define inside Connection String? The database name to connect to. 39. What‟s the data provider name to connect to Access database? Microsoft.Access.

40. What does Dispose method do with the connection object? Deletes it from the memory. 41. What is a pre-requisite for connection pooling? Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings 42. What‟s the implicit name of the parameter that gets passed into the class‟ set method? Value, and it‟s datatype depends on whatever variable we‟re changing. 43. How do you inherit from a class in C#? Place a colon and then the name of the base class. 44. Does C# support multiple inheritance? No, use interfaces instead. 45. When you inherit a protected class-level variable, who is it available to? Classes in the same namespace. 46. Are private class-level variables inherited? Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are. 47. Describe the accessibility modifier protected internal. It‟s available to derived classes and classes within the same Assembly (and naturally from the base class it‟s declared in). 48. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write? Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there‟s no implementation in it. 49. What‟s the top .NET class that everything is derived from? System.Object. 50. How‟s method overriding different from overloading? When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class. 51. What does the keyword virtual mean in the method definition? The method can be over-ridden. 52. Can you declare the override method static while the original method is nonstatic? No, you can‟t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override. 53. Can you override private virtual methods? No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access. 54. Can you prevent your class from being inherited and becoming a base class for some other classes? Yes, that‟s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It‟s the same concept as final class in Java. 55. Can you allow class to be inherited, but prevent the method from being overridden? Yes, just leave the class public and make the method sealed. 56. What‟s an abstract class? A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it‟s a blueprint for a class without any implementation.

57. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)? When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden. 58. What‟s an interface class? It‟s an abstract class with public abstract methods all of which must be implemented in the inherited classes. 59. Why can‟t you specify the accessibility modifier for methods inside the interface? They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it‟s public by default. 60. Can you inherit multiple interfaces? Yes, why not. 61. And if they have conflicting method names? It‟s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you‟re okay. 62. What‟s the difference between an interface and abstract class? In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes. 63. How can you overload a method? Different parameter data types, different number of parameters, different order of parameters. 64. If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor? Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class. 65. What‟s the difference between System.String and System.StringBuilder classes? System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed. 66. Is it namespace class or class namespace? The .NET class library is organized into namespaces. Each namespace contains a functionally related group of classes so natural namespace comes first.


				
DOCUMENT INFO
Shared By:
Stats:
views:805
posted:1/14/2010
language:English
pages:34