clarification of "this" keyword in Java

I have this code copied from Android developers website:

public class ExampleActivity extends Activity implements OnClickListener {
    protected void onCreate(Bundle savedValues) {
        ...
        Button button = (Button)findViewById(R开发者_StackOverflow.id.corky);
        button.setOnClickListener(this);
    }

    // Implement the OnClickListener callback
    public void onClick(View v) {
        // do something when the button is clicked
    }
    ...
}

I am wondering what exactly "this" keyword refers to? Does it refer to the class "ExampleActivity"? And in general how to find what "this" refers to?

It refers to the instance of ExampleActivity on which onCreate() has been called.

In general, from the Java Language Specification, 15.8.3:

The keyword this may be used only in the body of an instance method, instance initializer or constructor, or in the initializer of an instance variable of a class. If it appears anywhere else, a compile-time error occurs.

When used as a primary expression, the keyword this denotes a value that is a reference to the object for which the instance method was invoked (§15.12), or to the object being constructed. The type of this is the class C within which the keyword this occurs. At run time, the class of the actual object referred to may be the class C or any subclass of C.

this refers to the most inner class instance. In your example it refers to ExampleActivity which is of type OnClickListener which is passed in to setOnClickListener.

Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this.

Reference (from the Sun Java Tutorial):

• Using the this keyword
• Understanding Instance and Class Members

"this" is a reference to the current object.

In your case, it refers to an instance of the ExampleActivity class.

http://download.oracle.com/javase/tutorial/java/javaOO/thiskey.html

Yes, 'this' refers to the instance of the enclosing class.