Class definition inside method argument in Java?

Question

I have come across Java code in this form for the first time:

object.methodA(new ISomeName() {
public void someMethod() {
//some code
}
});

Answer 1

It's creating an anonymous class.

Note that within anonymous class, you can refer to final local variables from within the earlier code of the method, including final parameters:

final String name = getName();

Thread t = new Thread(new Runnable() {
    @Override public void run() {
        System.out.println(name);
    }
});
t.start();

The values of the variables are passed into the constructor of the anonymous class. This is a weak form of closures (weak because of the restrictions: only values are copied, which is why the variable has to be final).

Answer 2

It's called an Anonymous Class (PDF link).

Answer 3

this is called anonymous classes in Java. It means that you create anonymous class that implements ISomeName interface and is passed as argument to methodA.

Answer 4

This feature is called anonymous classes.