Re: can this be done with generics?

Robert Klemme <>
Mon, 25 Nov 2013 22:31:54 +0100
On 25.11.2013 12:59, Patrick Roemer wrote:

Responding to Andreas Leitgeb:

Is there a way to use *generics* for the methods of class Foo such that
each foo#() returns the *static* type on which the compiler saw it

Just a naive attempt... Not sure if this matches your use case and
requirements - this will only work for a one-level hierarchy with an
abstract root class and will probably require some ugly gymnastics
inside the Foo method implementations:

The approach is all but naive. And it can actually be made to work with
deeper hierarchies in a type safe way. There is only a single
@SuppressWarnings("unchecked") here:

package inh;

public class Foo<T extends Foo<?>> {

     public T foo() {
         System.out.println(getClass().getName() + " in foo()");
         return self();

     protected final T self() {
         return (T) this;

     public static void main(String[] args) {
         new Baz<Baz<?>>().foo().baz().bar();
         new TheEnd().foo().last().baz().bar();


class Bar<T extends Bar<?>> extends Foo<T> {
     public T bar() {
         System.out.println(getClass().getName() + " in bar()");
         return self();


class Baz<T extends Baz<?>> extends Bar<T> {
     public T baz() {
         System.out.println(getClass().getName() + " in baz()");
         return self();

final class TheEnd extends Baz<TheEnd> {
     public TheEnd last() {
         System.out.println(getClass().getName() + " in last()");
         return self();

A final class does not need a type parameter any more as it does not
need to propagate it.

Kind regards


remember.guy do |as, often| as.you_can - without end

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