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What is the difference between an Abstract class and Interface?


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Answered 2012-02-08 06:46:26
We can't instantiate both interfaces and abstract classes.

The only one difference between them is that an interface can't contain concrete(fully defined) methods where as an abstract class may contain them.

An abstract class not necessarily contain abstract methods. we can make a class as abstract class even it does not has any abstract methods.

When there is a need to write both abstract and concrete methods in a single unit we have to use an abstract class instead of an interface since an interface cant contain concrete methods.

All the fields(or properties) of an interface are by default 'static final' even when you don't mention explicitly. And all methods are 'public abstract'.

But in an abstract class we can have any type of fields and methods.

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