What does that Java construct do?

Question

I new to java so bear with me if this is a ridiculously simple question but I am curious about this method call which has {code} being taken in - see code below for an example in the method addSelectionListener. What is the purpose of this? I have been looking through docs for an explaination but cant seem to find what this practice is called never mind any useful information.

    setStatusLine.addSelectionListener(new SelectionAdapter() {
        public void widgetSelected(SelectionEvent e) {

            String message = "I would like to say hello to you.";
            if (pressed) {
                message = "Thank you for using me";
            }
            setStatusLine(message);
            pressed = !pressed;
        }
    });

Thanks for any help or insights that can be offered

Answer 1

this is an Anonymous Class, or Anonymous inner class. If you google for that you will find some tutorials/examples. Sun has some docs too.

Answer 2

As the other contributors already said: It is an Anonymous Class

You could have created a new class named MyClass in a new file called McClass.java looking like that:

class MyClass extends SelectionAdapter {

  public void widgetSelected(SelectionEvent e) {
    <your code that's being executed whenever the widget is being selected>
  }

}

Then you could have changed the first line like that:

setStatusLine.addSelectionListener(new MyClass());

See? Now you have an "explicit" class with just one function. Often that is too much overhead and would clutter your design.

Does that help?