Description Frank Tip 2003-08-26 12:08:36 EDT

If I extract an interface "I" from class "A" in the program below, which
contains method "zip()" but not method "zap()", the resulting program
will contain a compile-error.

The problem is the fact that the methods J.foo(A) and E.foo(A) in the 
example program are related, despite the fact that one does not override
the other. Therefore, the signature of these methods must either be
changed as a group, or they must not be changed at all. In this example,
we cannot change the signature of E.foo(A), so we can also not change
the signature of J.foo(A). 

I think the solution will be to generate additional type constraints
that enforce equality of parameter types and return types for such
methods, similar to the way overridden methods are currently handled.

  -Frank


package typeConstraintBug;

public class TypeConstraintBug {
	public static void main(String[] args){
		J j = new C();
		j.foo(new A());
		System.out.println("done");
	}
}

class A {
	public void zip(){ }
	public void zap(){ }
}

interface J {
	public void foo(A a1);
}
class B implements J {
	public void foo(A a3){
		a3.zip();
	}
}
class E {
	public void foo(A a4){
		a4.zap();
	}
}
class C extends E implements J  {
	/* no foo() here */
}