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/*
 * Copyright (c) 1997, 2017, 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
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 */
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
 * 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 static final Object[] NULL_ARRAY = new Object[0];
    
The list of ListenerType - Listener pairs 
/** The list of ListenerType - Listener pairs */
    protected transient volatile 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.

Returns:array of ListenerType-listener pairs
/**
     * 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.
     *
     * @return array of ListenerType-listener pairs
     */
    public Object[] getListenerList() {
        return listenerList;
    }

    
Return an array of all the listeners of the given type.

Params:
  • t – the type of EventListener classes to be returned
Type parameters:
  • <T> – the type of EventListener to search for
Throws:
Returns:all of the listeners of the specified type.
Since:1.3
/**
     * Return an array of all the listeners of the given type.
     *
     * @param <T> the type of {@code EventListener} to search for
     * @param t the type of {@code EventListener} classes to be returned
     * @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);
        @SuppressWarnings("unchecked")
        T[] result = (T[])Array.newInstance(t, n);
        int j = 0;
        for (int i = lList.length-2; i>=0; i-=2) {
            if (lList[i] == t) {
                @SuppressWarnings("unchecked")
                T tmp = (T)lList[i+1];
                result[j++] = tmp;
            }
        }
        return result;
    }

    
Returns the total number of listeners for this listener list.

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

    
Returns the total number of listeners of the supplied type
for this listener list.

Params:
  • t – the type of listeners to count
Returns:the number of listeners of type t
/**
     * Returns the total number of listeners of the supplied type
     * for this listener list.
     *
     * @param t the type of listeners to count
     * @return the number of listeners of type {@code t}
     */
    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 EventListener class to add
  • l – the listener to be added
Type parameters:
  • <T> – the type of EventListener to add
/**
     * Adds the listener as a listener of the specified type.
     *
     * @param <T> the type of {@code EventListener} to add
     * @param t the type of the {@code EventListener} class to add
     * @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
Type parameters:
  • <T> – the type of EventListener
/**
     * Removes the listener as a listener of the specified type.
     *
     * @param <T> the type of {@code EventListener}
     * @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);
            @SuppressWarnings("unchecked")
            Class<EventListener> tmp = (Class<EventListener>)Class.forName(name, true, cl);
            add(tmp, 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;
    }
}