The difference between an abstract class and an interface

Question

Possible duplicate:
Interface vs Base class

I do not understand the difference between an abstract class and an interface. When do I need to use what type of art?

Answer 1

When we create an interface , we basically create a set of methods without any implementation, which should be overridden by the implemented classes. The advantage is that it provides a way for the class to be part of two classes: one from the inheritance hierarchy and one from the interface.

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article along with the demo project discussed Interfaces versus Abstract classes.

Answer 2

:

abstract "is-a". Volkswagon - .

"can-do". IDrive.

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Answer 3

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public abstract class A {
    public string sayHi() { return "hi"; } // a method with code in it
    public abstract string sayHello();  // no implementation
}

public class B 
   : A
{
    // must implement, since it is not abstract
    public override string sayHello() { return "Hello from B"; }
}

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public interface A
{
    string sayHi(); // no implementation (code) allowed
    string sayHello();  // no implementation (code) allowed
}

public class B
    : A
{
     // must implement both methods
    string sayHi() { return "hi"; }
    string sayHello() { return "hello"; }
}

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class A {
    virtual int a() = 0;  // pure virtual function (no implementation)
}