Do I need a rebuild for Java here?

Question

I have a ClassA that is being used my many components and libraries in various areas of a project.
Now I need to add an extra member to this class but since it will not be needed/used by other areas it does not feel proper to extend the class.
If I add the member to ClassA instead of extending would I have any issues? Would everything need to be rebuild?

Answer 1

Adding a new member preserves binary compatibility, see also Chapter 13. Binary Compatibility of the Java Language specification.

Obviously you need to rebuild the modified class, but not classes which are using the modified one.

Answer 2

Unless your existing contacts and interactions between ClassA and other classes BREAK, there should be no issue. But if you change signature of a method that is used by other classes you could get a runtime error while locating the old version of method as it does not exist anymore.

Answer 3

If you change your Class A, obviously a rebuild is necessary. To minimize the impact you can extend the class A and use the subclass for your work. The other components and libraries will continue to keep using your Class A, while your code should now refer to the sublcass which has the added member.

Again, it depends on how you define your objects.