Object-Oriented Programming - .NET Interview Questions and Answers

Class:

1. A class is a reference type.
2. While instantiating a class, CLR allocates memory for its instance in heap.
3. Classes support inheritance.
4. Variables of a class can be assigned as null.
5. Class can contain constructor/destructor.

1. A structure is a value type.
2. In structure, memory is allocated on stack.
3. Structures do not support inheritance.
4. Structure members cannot have null values.
5. Structure does not require constructor/destructor and members can be initialiazed automatically.

Structures and classes are the two most important data structures that are used by programmers to build modular programs by using OOP languages, such as Visual Basic .NET, and Visual C#. The following are some of the similarities between a class and a structure:

• Access specifiers, such as public, private, and protected, are identically used in structures and classes to restrict the access of their data and methods outside their body.
• The access level for class members and struct members, including nested classes and structs, is private by default. Private nested types are not accessible from outside the containing type.
• Both can have constructors, methods, properties, fields, constants, enumerations, events, and event handlers.
• Both structures and classes can implement interfaces to use multiple-inheritance in code.
• Both structures and classes can have constructors with parameter.
• Both structures and classes can have delegates and events.

Each delegate object holds reference to a single method. However, it is possible for a delegate object to hold references of and invoke multiple methods. Such delegate objects are called multicast delegates or combinable delegates.

No. Two virtual methods must have the same signature.

The virtual keyword is used while defining a class to specify that the methods and the properties of that class can be overridden in derived classes.

Yes. Just declare the class public and make the method sealed.