Best C# Language Interview Questions and Answers

36. What are abstract classes?

What are the distinct characteristics of an abstract class? An abstract class is a class that cannot be instantiated and is always used as a base class. The following are the characteristics of an abstract class:

• You cannot instantiate an abstract class directly. This implies that you cannot create an object of the abstract class; it must be inherited.
• You can have abstract as well as non-abstract members in an abstract class.
• You must declare at least one abstract method in the abstract class.
• An abstract class is always public.
• An abstract class is declared using the abstract keyword.

The basic objective of an abstract class is to provide a common definition of the base class that multiple derived classes can share

37. Give a brief description of properties in C# and the advantages that are obtained by using them in programs.

In C#, a property is a way to reveal an internal data element of a class in a simple and intuitive manner. In other words, it is a simple extension of data fields. You can create a property by defining an externally available name and then writing the set and get property accessors. The get property accessor is used to return the property value. The set property accessor is used to assign a new value to the property.

38. Explain different types of inheritance.

Inheritance in OOP is of four types:

• Single inheritance - Contains one base class and one derived class
• Hierarchical inheritance - Contains one base class and multiple derived classes of the same base class
• Multilevel inheritance - Contains a class derived from a derived class
• Multiple inheritance - Contains several base classes and a derived class

 All .NET languages supports single, hierarchical, and multilevel inheritance. They do not support multiple inheritance because in these languages, a derived class cannot have more than one base class. However, you can implement multiple inheritance in.NET through interfaces.

39. You have defined a destructor in a class that you have developed by using the C# programming language, but the destructor never executed. Why did the destructor not execute?

 The runtime environment automatically invokes the extirpator of a class to release the resources that are place by variables and methods of an object. However, in C#, programmers cannot control the timing for invoking destructors, as Garbage Collector is only responsible for releasing the resources used by an object. Garbage Collector automatically gets information about unreferenced objects from .NET's runtime environment and then invokes the Finalize() method.

Although, it is not preferable to force Garbage Collector to perform garbage collection and retrieve all inaccessible memory, programmers can use the Collect() method of the Garbage Collector class to forcefully execute Garbage Collector.

40. What is a hashtable?

Hashtable is a data structure that accomplishes the IDictionary interface. It is used to store multiple items and each of these items is associated with a unique string key. Each item can be accessed using the key attached with it. In short, hashtable is an object holding the key-value pairs.

Best C# Language Interview Questions and Answers

31. What are methods?

   Methods are the building blocks of a class, in which they are associated together to share and process data to generate  the result. In other words, a method is a block of code that contains a series of assertions and illustrates the behavior of a class. While declaring a method you need to specify the access specifier, the return value, the name of the method, and the method parameters. All these associated together is called the signature of the method.

32. What is a namespace?

  Namespace is deliberated as a container that contains functionally related group of classes and other types.

33. Do events have return type?

   No, events do not have return type.

34. What is the function of the Try-Catch-Finally block?

   The try block encompasses those statements that can cause exception and the catch block handles the exception, if it occurs. Catch block contains the statements that have to be executed, when an exception occurs. The finally block always executes, irrespective of the fact whether or not an exception has occurred. The finally block is generally used to perform the cleanup process. If any exception occurs in the try block, the program control directly transfers to its corresponding catch block and later to the finally block. If no exception occurs inside the try block, then the program control transfers directly to the finally block.

35. How can you prevent a class from overriding in C# and Visual Basic?

  You can restrain a class from overriding in C# by using the sealed keyword; whereas, the NotInheritablekeyword is used to prevent a class from overriding in Visual Basic.

Best C# Language Interview Questions and Answers

26. What is a delegate?

A delegate is same as to a class which is used for storing the reference to a method and invocating that method at runtime , as required. A delegate can hold the reference of only those methods whose signatures are same as that of the delegate. Some of the examples of delegates are type-safe functions, pointers, or callbacks.

27. What is the syntax to inherit from a class in C#?

When a class is derived from another class, then the members of the base class become the members of the derived class. The access modifier used while accessing members of the base class secludes the access status of the base class members inside the derived class.

 The syntax to inherit a class from another class in C# is as follows: class MyNewClass : MyBaseclass 

28. State the features of an interface.

 An interface is a generic model that contains only the signature of methods. The signature of a method consists of the numbers of parameters, the type of parameter (value, reference, or output), and the order of parameters. An interface has no accomplishment on its own because it contains only the definition of methods without any method body. An interface is defined using the interface keyword. Moreover, you cannot instantiate an interface. The various features of an interface are as follows:

 • An interface is used to appliance multiple inheritance in code. This feature of an interface is quite different from that of abstract classes because a class cannot obtain the features of more than one class but can easily implement multiple interfaces.

• It defines a specific set of methods and their arguments.

• Variables in interface must be declared as public, static, and final while methods must be public and abstract.

• A class implementing an interface must implement all of its methods. • An interface can derive from more than one interface.

29. Can you use the 'throws' clause to raise an exception?

No, the throws clause cannot be used to raise an exception. The throw statement signals the instance of an exception during the execution of a program. When the program encounters a throw statement, the method terminates and returns the error to the calling method.

30. Define an array.

An array is considered as a homogeneous collection of elements, stored at contiguous memory locations, which can be referred by the same variable name. All the elements of an array variable can be accessed by index values. An Index value specifies the position of a particular element in an array variable.

Best C# Language Interview Questions and Answers

21. Is it a good practice to handle exceptions in code?

Yes, you must handle exceptions in code so that you can deal with any unexpected conditions that occur when a program is running. For example, dividing a number by zero or passing a string value to a variable that holds an integer value would result in an exception.

22. Explain the concept of constructor?

Constructor is an unique process of a class, which is called automatically when the sing of a class is created. It is created with the same name as the class and initializes all class members, whenever you access the class.

 The main features of a constructor are as follows:

• Constructors do not have any return type.
• Constructors can be overloaded.
• It is not mandatory to declare a constructor; it is invoked automatically by .NET Framework.

 23. Can you inherit private members of a class?

No, you cannot inherit private members of a class because private members are accessible only to that class and not outside that class.

24. Does .NET support multiple inheritance?

 .NET does not support multiple inheritance directly because in .NET, a class cannot inherit from more than one class. .NET supports multiple inheritance through interfaces

 25. How has exception handling changed in .NET Framework 4.0?

 In .NET 4.0, a new namespace, System.Runtime.ExceptionServices, has been inagvrated which contains the following classes for handling exceptions in a better and advanced manner:

• HandleProcessCorruptedStateExceptionsAttribute Class - Enables managed code to handle the corrupted state exceptions that occur in an operating system. These exceptions cannot be caught by specifying the try...catch block. To handle such exceptions, you can apply this attribute to the method that is assigned to handle these exceptions.

• FirstChanceExceptionEventArgs Class - Generates an event whenever a managed exception first occurs in your code, before the common language runtime begins searching for event handlers.