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.Net Object Oriented Programming Interview Questions and Answers for Freshers and Experience Part-3

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object oriented13. What is the difference between a class and a structure?

Class:

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

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

14. What are similarities between a class and a structure.

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.

15. What is a multicast delegate?

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.

16. Can you declare an overridden method to be static if the original method is not static?

No. Two virtual methods must have the same signature.

17. Why is the virtual keyword used in code?

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.

18. Can you allow a class to be inherited, but prevent a method from being overridden in C#?

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

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