Abstract method in Interface

You have no choice but to use an abstract method in an interface. Concrete methods are not permitted on an interface

I wonder, are you actually referring to the use of the "abstract" modifier on methods in an interface? That's superfluous, yes. I see this all the time, and the argument is that it clarifies for other developers that methods on the interface are abstract, but if a Java developer doesn't already understand that all methods on an interface are implicitly abstract, and doesn't understand that a method without a body must be abstract, I don't see what value that clarity provides anyway

georgemca at 2007-7-28 17:07:53 >

> Thanks for your answer.

>

> I can declare an abstract class which implementes an

> interface.

> The abstract class doesn't require the implementation

> of the methods

> declared in the interface.

>

> Why this?

Because the class is abstract.

A concrete class must provide (or inherit) implementations for all abstract methods in all its ancestor classes and for all methods in all interfaces it implements (and remember, all methods in an interface are abstract).

If a class does NOT have an implementation for one or more of those methods, the class must be declared abstract to indicate that.

> I don't understand because an abstract class can

> implements an interface!

Any class *can* be declared abstract (except final classes, I think).

Any class that doesn't have implementations for all its methods (including those from interfaces) *MUST* be declared abstract.

jverda at 2007-7-28 17:07:53 >