class A ...
class B extends A ...
class C extends A ...

String foo() ...
String bar(A a) ...

String r = (new B()).foo();
String r = (new B()).bar(new C());

A fred;
List as = new LinkedList();
for (A a : as) ... fred.bar(a); ...

class A<T,U,V> ...
class B<T> extends A<T,Void,Object> ...
class C<N> extends A<String,Void,Object> ...

T foo() ...

String r = (new A<String,Void,Object>()).foo();
String r = (new B<String>()).foo();
String r = (new C<Integer>()).foo();

String r = (new B<String>()).foo();
String r = (new B<String>()).bar(new C<Integer>());

A<String,String,Integer> fred;
List<A<String,String,Integer>> as = new LinkedList<>();
for (A a : as) ... fred.bar(a); ...