What is the difference between an interface and an abstract class? [duplicate]

Question

Possible Duplicate:
Interface vs Abstract Class (general OO)

I'm not exactly clear on the difference.

Thanks

Answer 1

They are quite similar but there are some important technical differences:

• An abstract class allows you to provide a default implementation for some of the methods but an interface does not allow you to provide any implementations.
• You can implement multiple interfaces but you can only inherit from one abstract class.

These differences affect how the two techniques should be used:

• You should use an interface to define a contract.
• An abstract class can be useful to reuse code... but be aware that it is not the only way to reuse code. You should also consider other approaches such as containment.

Answer 2

An interface doesn't allow definition of any of the member methods, whereas an abstract class does allow some or all to be defined. A class however can only extend one class (abstract or not) but can implement as many interfaces as it wants.