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EventListenerList.java
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1998-11-09
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/*
* @(#)EventListenerList.java 1.18 98/02/02
*
* Copyright (c) 1997 Sun Microsystems, Inc. All Rights Reserved.
*
* This software is the confidential and proprietary information of Sun
* Microsystems, Inc. ("Confidential Information"). You shall not
* disclose such Confidential Information and shall use it only in
* accordance with the terms of the license agreement you entered into
* with Sun.
*
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
* SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
* IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
* PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
* SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
* THIS SOFTWARE OR ITS DERIVATIVES.
*
*/
package javax.awt.swing.event;
import java.io.*;
import java.util.*;
/**
* A class which holds a list of EventListeners. A single instance
* can be used to hold all listeners (of all types) for the instance
* using the lsit. 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 which this class provides are that it is relatively
* cheap in the case of no listeners, and provides serialization for
* eventlistener lists in a single place, as well as a degree of MT safety
* (when used correctly).
*
* Usage example:
* Say one is defining a class which sends out FooEvents, and wantds
* 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 listenrList = new EventListnerList();
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 Method to the
* appropriate method name (one fire method should exist for each
* notification method in the FooListener interface).
* <p>
* Warning: 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 Swing1.0 applications. It will
* not be possible to load serialized Swing1.0 objects with future releases
* of Swing. The JDK1.2 release of Swing will be the compatibility
* baseline for the serialized form of Swing objects.
*
* @version 1.18 02/02/98
* @author Georges Saab
* @author Hans Muller
* @author James Gosling
*/
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;
/**
* This 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 listner 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 the total number of listeners for this listenerlist
*/
public int getListenerCount() {
return listenerList.length/2;
}
/**
* Return the total number of listeners of the supplied type
* for this listenerlist.
*/
public int getListenerCount(Class t) {
int count = 0;
Object[] lList = listenerList;
for (int i = 0; i < lList.length; i+=2) {
if (t == (Class)lList[i])
count++;
}
return count;
}
/**
* Add 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 void add(Class t, EventListener l) {
if (!t.isInstance(l)) {
throw new IllegalArgumentException("Listener " + l +
" is not of type " + t);
}
if (l ==null) {
throw new IllegalArgumentException("Listener " + l +
" is null");
}
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;
}
}
/**
* Remove 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 void remove(Class t, EventListener l) {
if (!t.isInstance(l)) {
throw new IllegalArgumentException("Listener " + l +
" is not of type " + t);
}
if (l ==null) {
throw new IllegalArgumentException("Listener " + l +
" is null");
}
// 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] == l)) {
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())) {
EventListener l = (EventListener)s.readObject();
add(Class.forName((String)listenerTypeOrNull), l);
}
}
/**
* Return 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;
}
}