How to create a class that “extends” two existing concrete classes

Question

I very well know that it can be done with the help of interfaces and i have done it many times. But this time my situation is quite difference. I have class A ,

Answer 1

Maybe you can create a new class D, and have both class A and class B inherit from D?

Answer 2

You may try create class C that will contain one instance of class A and one of class B and their methods (create methods with same names that will just call methods from A and B), it's called Composition - another method in opposite to inheritance. Of course that's in case if you don't need instanceof to work with that C class.

Answer 3

Change the way you are thinking. Think in interfaces. It means that class A is actually an implementation of interface A' and class B is an implementation of interface B'. And you actually want a class C that implements both interfaces A' and B'. Class C doesn't need to extend anything or to use any particular pattern or whatsoever. It can extend A and delegate some methods to B, or it can extend B and delegate some methods to A. Or it can delegate all methods to A and B - implementation is your decision.

Answer 4

It is not possible to extend two classes, and thus inherit functionality from both, in Java. Your easiest alternative it to "wrap" at least one of the two classes. So, instead of also extending B you can have an instance of B inside C, and declare each of B's methods on C, and pass them through. C would not "be" a B, but it sounds like you just want to inherit functionality. And if that's true of A too, then, well, you should be using this pattern for both A and B and not extending either.

Answer 5

Make use of composition. Class C will contain an instance each of classes A and B.

Answer 6

http://en.wikipedia.org/wiki/Adapter_pattern

Your problem is solved by the adapter pattern. I went back to check the wiki document, just to be sure :)