Differences between Interfaces and Abstract Classes

Q

What's the difference between an interface and an abstract class?

✍: FYIcenter

A

An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.

Interfaces provide a form of multiple inheritance. A class can extend only one other class. Interfaces are limited to public methods and constants with no implementation.

Abstract classes can have a partial implementation, protected parts, static methods, etc. A Class may implement several interfaces. But in case of abstract class, a class may extend only one abstract class.

Interfaces are slow as it requires extra indirection to to find corresponding method in in the actual class. Abstract classes are fast.

Neither Abstract classe or Interface can be instantiated.

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