Java: Why anonymous inner classes can access methods of outer class?

Question

Lately I've found out that this works, although I'd expect it not to:

class Outer
{ 
    Button b;

    void foo() {}


    void bar()
    {
        b = new Button();
        b.setOnClickListener(new OnClickListener(){
            @Override
            public void OnClick()
            {
               foo();
            }
        }); 
    }
}

I'd expect Outer.this.foo() to be required, but seems that simply foo() also works. Could someone tell me when exactly this was added to the language? Please help me understand exact name resolution rules here. Thanks!

The questions:

1) Why is this working?

2) If this works, why do we need the "Outer.this" syntax?

No, I just want to understand the exact name resolution rules here. — Alex Jenter, Jun 08 '14 at 15:31
I don't find your question very useful. Also asking for off site resources is off-topic. — Sotirios Delimanolis, Jun 08 '14 at 15:31
If your comment is your actual question, that changes a lot. — Sotirios Delimanolis, Jun 08 '14 at 15:31
I believe inner classes were added back in Java 1.1, which is about in 1997... — Natix, Jun 08 '14 at 15:32
Do you mean that inner classes always have been able to access outer classes's methods even without the "Outer.this" qualification? Why do we need Outer.this then? — Alex Jenter, Jun 08 '14 at 15:35

score 2 · Accepted Answer · answered Jun 08 '14 at 15:38

The possibility to call methods like this has existed since the inner classes had been introduced. The mechanism for resolving the instance that a method is called on is described in detail in Java Language Specification, Section 15.12.4.1., Compute Target Reference (If Necessary).

You are probably refering to the fact that you don't need the "Qualified this". But this this is mainly intended to resolve ambiguities when the inner instance and the outer instance have a method with the same signature.

Java: Why anonymous inner classes can access methods of outer class?

1 Answers1