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/* * @(#)EventListenerList.java 1.37 05/11/17 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package javax.swing.event; import java.io.*; import java.util.*; import java.lang.reflect.Array; /** * 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<sup><font size="-2">TM</font></sup> * has been added to the <code>java.beans</code> package. * Please see {@link java.beans.XMLEncoder}. * * @version 1.37 11/17/05 * @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; /** * 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(); add((Class<EventListener>)Class.forName((String)listenerTypeOrNull, 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; } }