Re: Generics puzzle with implements Comparable

On May 20, 10:17 pm, Roedy Green <see_webs...@mindprod.com.invalid>
wrote:


If class Foo is comparable to other instances of class Foo, then
subclass Bar of Foo must also be comparable to other instances of
class Foo. Thus, the subclass must also implement Comparable<Foo> --
which it does anyways, via inheritance. You also can't implement the
same interface twice, and two generics specializations of an interface
are actually the same interface under the hood.

You'll have to either do double-dispatch tricks or check which
subclass is involved on the right in the derived class' compareTo
method.

This isn't entirely a generics-related problem. The following might
demonstrate the issue:

class Foo {
  public void frobWith(Foo otherFoo) {...}
}

class Bar extends Foo {
  public void frobWith(Bar otherBar) {...}
}

The derived class' frobWith method doesn't actually override the
parent class's and won't be called via dynamic dispatch.