Implementing Comparable for multiple types

Question

I am currently refactoring some legacy code to make use of Java 5's generics, and I ran into a problem.
Foo extends Parent and implements Comparable. Bar is a sibling of Foo and does not implement Comparable. Now, in the legacy code, Foo is Comparable to both Foo and Bar, and in order to use generics, I have to specify a single class or use wild cards with "extends". I know I could resolve this problem by using <? extends Parent>, but I am reluctant to do this, because Foo and Bar also have about 30 other siblings.
Is there anyway that I can use generics and only let the two classes, Foo and Bar be Comparable to Foo?

Answer 1

I quite don't get what the legacy code does. If Bar does not implement comparable, how is Foo comparable to Bar? I think, this quite violates the rules for implementing Comparable.
You don't have to implement an additional class, though, but might work with an interface, which both Foo and Bar implement and which extends Comparable on the interface.
Maybe I should give an abstract example on my confusing statement. :)
interface FooBar extends Comparable<FooBar> { ...}
class Foo implements FooBar { ... }
class Bar implements FooBar { ... }