Java: How do I add to a base class without modifying class file

Question

I am using a Java library that has a class hierarchy:

e.g. classes C1 and C2 that both extend class B

Is there a way for me to add functionality (attributes, methods) to class B such that it will be available to the child classes C1 & C2 without modifying the 3 files?

If not, what is the right way to do this short of rewriting all 3 classes?

Answer 1

Assuming you aren't able to modify B for some reason, make an intermediary class that extends it for you:

public class ClassC extends ClassB {

    //additional functionality

}

Then it's simple:

public class Class1 extends ClassC {...}

If you can modify B, the other classes already inherit the methods, and you don't need to worry about rewriting them unless you mark the methods abstract