Must an abstract class have an abstract method?

/**/ /*
* @ (#) Windowadapter.java 1.18 01/12/03
*
* Copyright 2002 Sun Microsystems, Inc. All rights reserved.
* SUN proprietary/confidential. Use are subject to license terms.
*/

Package java.awt. event;

/**/ /**
* An abstract adapter class for receiving window events.
* The methods in this class are empty. This class exists as
* Convenience for creating listener objects.
* <P>
* Extend This class to create a <code>WindowEvent</code> listener
* and override the methods for the events of interest. (If you implement the
* <code>WindowListener</code> interface, have to define all
* The methods in it. This abstract class defines NULL methods for them
* All, so your can only have to define methods for the events you care about.)
* <P>
* Create a Listener object using the extended class and then register it with
* A window using the window ' s <code>addWindowListener</code>
* method. When the window ' s status is changes by virtue of being opened,
* closed, activated or deactivated, iconified or deiconified,
* The relevant method in the listener
* object is invoked, and the <code>WindowEvent</code> are passed to it.
*
* @see WindowEvent
* @see WindowListener
* @see <a href= "http://java.sun.com/docs/books/tutorial/post1.0/ui/windowlistener.html" >tutorial:writing A Window listener</a>
* @see <a href= "http://www.awl.com/cp/javaseries/jcl1_2.html" >reference:the Java Class Libraries (update file) </a>
*
* @author Carl Quinn
* @author Amy Fowler
* @author David Mendenhall
* @version 1.18, 12/03/01
* @since 1.1
*/
Public abstract class Windowadapter
Implements WindowListener, Windowstatelistener, Windowfocuslistener
... {
/**//**
* Invoked when a window has been opened.
*/
public void windowopened (WindowEvent e) ... {}

/**//**
* Invoked when a window was in the process of being closed.
* The close operation can is overridden at this point.
*/
public void windowclosing (WindowEvent e) ... {}

/**//**
* Invoked when a window has been closed.
*/
public void windowclosed (WindowEvent e) ... {}

/**//**
* Invoked when a window is iconified.
*/
public void windowiconified (WindowEvent e) ... {}

/**//**
* Invoked when a window is de-iconified.
*/
public void windowdeiconified (WindowEvent e) ... {}

/**//**
* Invoked when a window is activated.
*/
public void windowactivated (WindowEvent e) ... {}