Any good way to declare method as `return this`?

Something like this:

class C 开发者_开发问答{

    typeof(this) foo() { return this; }

}

Well, I know it's impossible in Java 6, so I'll be glad to hear if I can do it in Java 7.

EDIT

This should be useful for chaining method calls, and avoid to create temporary local variables, like this:

class Entity {

    typeof(this) refresh();

    typeof(this) clone();

    typeof(this) detach();

}

class FooEntity extends Entity {

    @Override
    typeof(this) detach() {
        fooLink21.removeRef(this); 
        bar39.detach(); 
        return this; 
    }

    void doSomeInteresting() {}
}

fooEntity.clone().detach().doSomeInteresting();

and lot more.

I deem it should be very easy to add this function to compiler, well maybe I should hack into openjdk or gcj maybe?

BTW, I had never succeeded to rebuild the openjdk.

If you would use generics it might look a little bit like this:

class Parent<C extends Parent> {

   public C getMe (){
      return this;
   }
}

class Sub extends Parent<Sub> { }

It might work, but I wouldn't suggest writing code like this. It's bad design...

I don't think there's any way to do this, in either Java 6 or Java 7. Adding it would not be easy - i think the return type would be what's called a 'dependent type', and that's something from a far more complicated type system than Java has at present.

Gressie's answer about adding a type parameter to the base class is the only way to get close to what you want, as far as i know.

However, if you were prepared to use a helper function, you could do it without a type parameter on the class:

abstract class Entity {
    public static <T extends Entity> T detach(T entity) {
        entity.detach();
        return entity;
    }
    protected abstract void detach();
}

You could then say:

import static Entity.detach;

detach(fooEntity).doSomeInteresting();

That's pretty clunky, though.

I do not know much about Java (Second year SD student using primarily C#/C++), but you may want to look at Generics. If they are what I think they are in relation to C++, C#, they are like Templates, where you can write methods that return a Template type.

http://en.wikipedia.org/wiki/Generics_in_Java

From what it looks like you are doing, why not use a constructor? It also looks like you may be asking how to return a method? If so:

You can return a method in Java. I highly suggest you don't and consider alternatives to this practice. Have a look at java.lang.reflect ; provides access to methods, fields and constructors. Java is not 'meant' to deal with first-class functions. If you DO decide to do this, be prepared for a lot of catch statements...