/*
 * 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:
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);
        }
    }
}
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.

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 applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

Author:Georges Saab, Hans Muller, James Gosling
/** * 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&gt;=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&trade; * 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.
/** * 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.
Throws:
Returns:all of the listeners of the specified type.
Since:1.3
/** * 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.
/** * 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.
/** * 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.
Params:
  • t – the type of the listener to be added
  • l – the listener to be added
/** * 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.
Params:
  • t – the type of the listener to be removed
  • l – the listener to be removed
/** * 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.
/** * 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; } }