Interface implementation syntax sugar with SWT ?

[Senhor Ignoradoo]

Hi, i have this snippet from SWT:

    
/*******************************************************************************
 * Copyright (c) 2000, 2005 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.snippets;

/*
 * Make a toggle button have radio behavior
 *
 * For a list of all SWT example snippets see
 * http://www.eclipse.org/swt/snippets/
 */

import org.eclipse.swt.*;
import org.eclipse.swt.widgets.*;
import org.eclipse.swt.layout.*;

public class Snippet169 {
public static void main (String [] args) {
	Display display = new Display ();
	final Shell shell = new Shell (display);
	shell.setLayout (new FillLayout ());
	Listener listener = new Listener () {
		public void handleEvent (Event e) {
			Control [] children = shell.getChildren ();
			for (int i=0; i<children.length; i++) {
				Control child = children [i];
				if (e.widget != child && child instanceof Button && (child.getStyle () & SWT.TOGGLE) != 0) {
					((Button) child).setSelection (false);
				}
			}
			((Button) e.widget).setSelection (true);
		}
	};
	for (int i=0; i<20; i++) {
		Button button = new Button (shell, SWT.TOGGLE);
		button.setText ("B" + i);
		button.addListener (SWT.Selection, listener);
		if (i == 0) button.setSelection (true);
	}
	shell.pack ();
	shell.open ();
	while (!shell.isDisposed ()) {
		if (!display.readAndDispatch ()) display.sleep ();
	}
	display.dispose ();
}
}

I understad all the code, except:

   
Listener listener = new Listener () {
		public void handleEvent (Event e) {
			Control [] children = shell.getChildren ();
			for (int i=0; i<children.length; i++) {
				Control child = children [i];
				if (e.widget != child && child instanceof Button && (child.getStyle () & SWT.TOGGLE) != 0) {
					((Button) child).setSelection (false);
				}
			}
			((Button) e.widget).setSelection (true);
		}
	};
 

Looks like it´s implementing an interface ? Can somebody provide me an explanation or a link to some book that explains that ?

Thanks in advance.

[Jason Irwin]

It's creating a Listener instance and using an in-line declaration to override the "handleEvent" method, that's what seems to contain the logic for the toggle button -> radio button behavioural change mentions in the comment header.

J.

[Vijitha Kumara]

That's an anonymous inner class example. That's probably the only place you will apply "new" keyword to the name of an interface. That's how you create an object of a class which implements an interface. The class implementing the interface becomes anonymous here as you have a reference of type interface to an object of that class. Nested classes from SUN tutorials gives you a brief explanation.

[Senhor Ignoradoo]

Thanks. I got now :-).

[Jesper de Jong]

Sr Ignorado, please check your private messages for an administrative matter.