This program doesn't compile:

class Foo<X> {
   <Z> Foo test() { return null; }
   Foo<?> foo = test();
}

The compiler reports the following message:

Test.java:3: error: incompatible types; no instance(s) of type variable(s) Z exist so that Foo conforms to Foo<?>
   Foo<?> foo = test();
                    ^
  required: Foo<?>
  found: <Z>Foo
  where Z is a type-variable:
    Z extends Object declared in method <Z>test()
1 error