Dear all,

sorry, I'm still confused about instanceof and generics although I read
several good introductions and explanations.

My question is:  If A is an abstract class, how can I write a test that
succeeds for all instances
of subclasses of A (and fails for all others ;-)?

I short, I have the following situation:
I have an abstract class A with several subclasses B, C, ...

There is an easy way of comparing subclasses of A for equality.  In
particular, this comparison gurarantees that no two instances of
subclasses of A are found to be equal unless they are an instance of
the same subclass.

In other words "boolean equal(Object other)" can be the same for all
subclasses of A and therefore I want to override it in A.

My approach is

@Override
boolean equals(Object other)
{
    if(!(other instanceof A))
    {
         // error
    }

    return compare(this, (A) other);
}

But that does not work because !(other instanceof A) is true for all
instances of subclasses of A.

How can I write a test that succeeds for all subclasses of A?

Thank you,

Uli