Back to index...

	/*
	* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	package javax.swing.event;

	import java.io.*;
	import java.util.*;
	import java.lang.reflect.Array;
	import sun.reflect.misc.ReflectUtil;

	/**
	* A class that holds a list of EventListeners. A single instance
	* can be used to hold all listeners (of all types) for the instance
	* using the list. It is the responsiblity of the class using the
	* EventListenerList to provide type-safe API (preferably conforming
	* to the JavaBeans spec) and methods which dispatch event notification
	* methods to appropriate Event Listeners on the list.
	*
	* The main benefits that this class provides are that it is relatively
	* cheap in the case of no listeners, and it provides serialization for
	* event-listener lists in a single place, as well as a degree of MT safety
	* (when used correctly).
	*
	* Usage example:
	* Say one is defining a class that sends out FooEvents, and one wants
	* to allow users of the class to register FooListeners and receive
	* notification when FooEvents occur. The following should be added
	* to the class definition:
	* <pre>
	* EventListenerList listenerList = new EventListenerList();
	* FooEvent fooEvent = null;
	*
	* public void addFooListener(FooListener l) {
	* listenerList.add(FooListener.class, l);
	* }
	*
	* public void removeFooListener(FooListener l) {
	* listenerList.remove(FooListener.class, l);
	* }
	*
	*
	* // Notify all listeners that have registered interest for
	* // notification on this event type. The event instance
	* // is lazily created using the parameters passed into
	* // the fire method.
	*
	* protected void fireFooXXX() {
	* // Guaranteed to return a non-null array
	* Object[] listeners = listenerList.getListenerList();
	* // Process the listeners last to first, notifying
	* // those that are interested in this event
	* for (int i = listeners.length-2; i>=0; i-=2) {
	* if (listeners[i]==FooListener.class) {
	* // Lazily create the event:
	* if (fooEvent == null)
	* fooEvent = new FooEvent(this);
	* ((FooListener)listeners[i+1]).fooXXX(fooEvent);
	* }
	* }
	* }
	* </pre>
	* foo should be changed to the appropriate name, and fireFooXxx to the
	* appropriate method name. One fire method should exist for each
	* notification method in the FooListener interface.
	* <p>
	* <strong>Warning:</strong>
	* Serialized objects of this class will not be compatible with
	* future Swing releases. The current serialization support is
	* appropriate for short term storage or RMI between applications running
	* the same version of Swing. As of 1.4, support for long term storage
	* of all JavaBeans™
	* has been added to the <code>java.beans</code> package.
	* Please see {@link java.beans.XMLEncoder}.
	*
	* @author Georges Saab
	* @author Hans Muller
	* @author James Gosling
	*/
	@SuppressWarnings("serial")
	public class EventListenerList implements Serializable {
	/* A null array to be shared by all empty listener lists*/
	private final static Object[] NULL_ARRAY = new Object[0];
	/* The list of ListenerType - Listener pairs */
	protected transient Object[] listenerList = NULL_ARRAY;

	/**
	* Passes back the event listener list as an array
	* of ListenerType-listener pairs. Note that for
	* performance reasons, this implementation passes back
	* the actual data structure in which the listener data
	* is stored internally!
	* This method is guaranteed to pass back a non-null
	* array, so that no null-checking is required in
	* fire methods. A zero-length array of Object should
	* be returned if there are currently no listeners.
	*
	* WARNING!!! Absolutely NO modification of
	* the data contained in this array should be made -- if
	* any such manipulation is necessary, it should be done
	* on a copy of the array returned rather than the array
	* itself.
	*/
	public Object[] getListenerList() {
	return listenerList;
	}

	/**
	* Return an array of all the listeners of the given type.
	* @return all of the listeners of the specified type.
	* @exception ClassCastException if the supplied class
	* is not assignable to EventListener
	*
	* @since 1.3
	*/
	public <T extends EventListener> T[] getListeners(Class<T> t) {
	Object[] lList = listenerList;
	int n = getListenerCount(lList, t);
	T[] result = (T[])Array.newInstance(t, n);
	int j = 0;
	for (int i = lList.length-2; i>=0; i-=2) {
	if (lList[i] == t) {
	result[j++] = (T)lList[i+1];
	}
	}
	return result;
	}

	/**
	* Returns the total number of listeners for this listener list.
	*/
	public int getListenerCount() {
	return listenerList.length/2;
	}

	/**
	* Returns the total number of listeners of the supplied type
	* for this listener list.
	*/
	public int getListenerCount(Class<?> t) {
	Object[] lList = listenerList;
	return getListenerCount(lList, t);
	}

	private int getListenerCount(Object[] list, Class t) {
	int count = 0;
	for (int i = 0; i < list.length; i+=2) {
	if (t == (Class)list[i])
	count++;
	}
	return count;
	}

	/**
	* Adds the listener as a listener of the specified type.
	* @param t the type of the listener to be added
	* @param l the listener to be added
	*/
	public synchronized <T extends EventListener> void add(Class<T> t, T l) {
	if (l==null) {
	// In an ideal world, we would do an assertion here
	// to help developers know they are probably doing
	// something wrong
	return;
	}
	if (!t.isInstance(l)) {
	throw new IllegalArgumentException("Listener " + l +
	" is not of type " + t);
	}
	if (listenerList == NULL_ARRAY) {
	// if this is the first listener added,
	// initialize the lists
	listenerList = new Object[] { t, l };
	} else {
	// Otherwise copy the array and add the new listener
	int i = listenerList.length;
	Object[] tmp = new Object[i+2];
	System.arraycopy(listenerList, 0, tmp, 0, i);

	tmp[i] = t;
	tmp[i+1] = l;

	listenerList = tmp;
	}
	}

	/**
	* Removes the listener as a listener of the specified type.
	* @param t the type of the listener to be removed
	* @param l the listener to be removed
	*/
	public synchronized <T extends EventListener> void remove(Class<T> t, T l) {
	if (l ==null) {
	// In an ideal world, we would do an assertion here
	// to help developers know they are probably doing
	// something wrong
	return;
	}
	if (!t.isInstance(l)) {
	throw new IllegalArgumentException("Listener " + l +
	" is not of type " + t);
	}
	// Is l on the list?
	int index = -1;
	for (int i = listenerList.length-2; i>=0; i-=2) {
	if ((listenerList[i]==t) && (listenerList[i+1].equals(l) == true)) {
	index = i;
	break;
	}
	}

	// If so, remove it
	if (index != -1) {
	Object[] tmp = new Object[listenerList.length-2];
	// Copy the list up to index
	System.arraycopy(listenerList, 0, tmp, 0, index);
	// Copy from two past the index, up to
	// the end of tmp (which is two elements
	// shorter than the old list)
	if (index < tmp.length)
	System.arraycopy(listenerList, index+2, tmp, index,
	tmp.length - index);
	// set the listener array to the new array or null
	listenerList = (tmp.length == 0) ? NULL_ARRAY : tmp;
	}
	}

	// Serialization support.
	private void writeObject(ObjectOutputStream s) throws IOException {
	Object[] lList = listenerList;
	s.defaultWriteObject();

	// Save the non-null event listeners:
	for (int i = 0; i < lList.length; i+=2) {
	Class<?> t = (Class)lList[i];
	EventListener l = (EventListener)lList[i+1];
	if ((l!=null) && (l instanceof Serializable)) {
	s.writeObject(t.getName());
	s.writeObject(l);
	}
	}

	s.writeObject(null);
	}

	private void readObject(ObjectInputStream s)
	throws IOException, ClassNotFoundException {
	listenerList = NULL_ARRAY;
	s.defaultReadObject();
	Object listenerTypeOrNull;

	while (null != (listenerTypeOrNull = s.readObject())) {
	ClassLoader cl = Thread.currentThread().getContextClassLoader();
	EventListener l = (EventListener)s.readObject();
	String name = (String) listenerTypeOrNull;
	ReflectUtil.checkPackageAccess(name);
	add((Class<EventListener>)Class.forName(name, true, cl), l);
	}
	}

	/**
	* Returns a string representation of the EventListenerList.
	*/
	public String toString() {
	Object[] lList = listenerList;
	String s = "EventListenerList: ";
	s += lList.length/2 + " listeners: ";
	for (int i = 0 ; i <= lList.length-2 ; i+=2) {
	s += " type " + ((Class)lList[i]).getName();
	s += " listener " + lList[i+1];
	}
	return s;
	}
	}

Back to index...