Why can't I use .this in anonymous class?

Question

I recently use this code, and realize that in anonymous class, I can't access the instance by .this, like this:

Sprite sprFace = new Sprite() {

    @Override
    protected void onManagedUpdate(float pSecondElapsed) {
        runOnUpdateThread(new Runnable() {

        @Override
        protected void run() {    
            Sprite.this.getParent().detach(Sprite.this); // Here
        }});
    }

};

I know how to solve it (just declare a "me" variable), but I need to know why I can't use <Class>.this?

@Thilo Sorry I have a typo mistake. me will return the Runnable. — Luke Vo, Aug 18 '11 at 06:47

score 4 · Accepted Answer · answered Aug 18 '11 at 06:11

The <Class>.this syntax gives a special way of referring to the object of type <Class>, as opposed to the shadowing type.

In addition, <Class> must be the name of the type you're trying to access. In your case, Sprite is not the actual type of sprFace. Rather, sprFace is an instance of an anonymous subclass of Sprite, thus the syntax is not applicable.

score 1 · Answer 2 · answered Aug 18 '11 at 06:30

1

The type of the outer object is not Sprite, but rather an anonymous subclass of Sprite and you have no way of naming this anonymous subclass in your code.

In this case you need a name to refer to and therefore an anonymous class will not do the job. You can use a local class instead (which behaves as an anonymous class with a name). In the code block, you can write:

class MySprite extends Sprite {

    @Override
    protected void onManagedUpdate(float pSecondElapsed) {
        runOnUpdateThread(new Runnable() {
            MySprite.this.getParent().detach(MySprite.this); // Here
        });
    }

};

Sprite sprFace = new MySprite();

answered Aug 18 '11 at 06:30

Mathias Schwarz

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But that would be the same as just saying `this.getParent()` or `getParent()` – Thilo Aug 18 '11 at 06:34
Thanks for your answer, but I'd rather declare me variant. – Luke Vo Aug 18 '11 at 06:38
W.N.: I don't know what you mean by 'declare me variant'. – Mathias Schwarz Aug 18 '11 at 06:51
Thile: No. Notice that there is an anonymous `Runnable` inside the anonymous `Sprite`. `this` would refer to the `Runnalbe` instance. – Mathias Schwarz Aug 18 '11 at 06:51
Sorry for my bad English. `private Sprite me = this` – Luke Vo Aug 18 '11 at 06:55
@Mathias. Okay maybe. But without the `this`, any `getParent` from parent or containing class should be accessible unless shadowed. – Thilo Aug 18 '11 at 07:04
1

@Thilo: But you can't use get the object for the method parameter. – Luke Vo Aug 18 '11 at 07:10
@Thilo: Yes, but it could be shadowed. We cannot tell from the code given and there is probably a reason why W.N. asks... – Mathias Schwarz Aug 18 '11 at 08:45
The reason he asked was more for the method parameter, I think. – Thilo Aug 18 '11 at 08:49

Why can't I use .this in anonymous class?

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