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From: Robert Klemme <shortcutter@googlemail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: can this be done with generics?
Date: Mon, 25 Nov 2013 22:31:54 +0100
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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
>> applied?
>
> 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();
     }

     @SuppressWarnings("unchecked")
     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

	robert



-- 
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