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jlechner |
/* EventListenerList.java --
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Copyright (C) 2002, 2004, 2005 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package javax.swing.event;
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import java.io.Serializable;
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import java.lang.reflect.Array;
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import java.util.EventListener;
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/**
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* A utility class for keeping track of {@link EventListener}s.
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*
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* <p><b>Example for using this class:</b>
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*
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* <blockquote><pre> import java.util.EventListener;
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* import javax.swing.event.EventListenerList;
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*
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* class Foo
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* {
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* protected final EventListenerList listeners = new EventListenerList();
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* protected BarClosedEvent barClosedEvent = null;
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*
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* public void addBarListener(BarListener l)
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* {
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* listeners.<a href="#add(java.lang.Class, java.util.EventListener)"
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* >add</a>(BarListener.class, l);
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* }
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*
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* public void removeBarListener(BarListener l)
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* {
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* listeners.<a href="#remove(java.lang.Class, java.util.EventListener)"
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* >remove</a>(BarListener.class, l);
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* }
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*
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* protected void fireBarClosedEvent()
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* {
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* Object[] l = listeners.<a href="#getListenerList()"
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* >getListenerList()</a>;
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*
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* for (int i = l.length - 2; i >= 0; i -= 2)
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* if (l[i] == BarListener.class)
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* {
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* // Create the event on demand, when it is needed the first time.
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* if (barClosedEvent == null)
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* barClosedEvent = new BarClosedEvent(this);
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*
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* ((BarClosedListener) l[i + 1]).barClosed(barClosedEvent);
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* }
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* }
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* }</pre></blockquote>
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*
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* @author Andrew Selkirk (aselkirk@sympatico.ca)
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* @author Sascha Brawer (brawer@dandelis.ch)
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*/
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public class EventListenerList
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implements Serializable
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{
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/**
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* An ID for serializing instances of this class; verified with the
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* serialver tool of Sun J2SE 1.4.1_01.
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*/
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static final long serialVersionUID = -5677132037850737084L;
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/**
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* An empty array that is shared by all instances of this class that
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* have no listeners.
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*/
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private static final Object[] NO_LISTENERS = new Object[0];
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/**
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* An array with all currently registered listeners. The array has
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* twice as many elements as there are listeners. For an even
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* integer <code>i</code>, <code>listenerList[i]</code> indicates
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* the registered class, and <code>listenerList[i+1]</code> is the
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* listener.
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*/
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protected transient Object[] listenerList = NO_LISTENERS;
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/**
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* EventListenerList constructor
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*/
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public EventListenerList()
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{
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// Nothing to do here.
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}
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/**
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* Registers a listener of a specific type.
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*
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* @param t the type of the listener.
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*
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* @param listener the listener to add, which must be an instance of
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* <code>t</code>, or of a subclass of <code>t</code>.
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*
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* @throws IllegalArgumentException if <code>listener</code> is not
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* an instance of <code>t</code> (or a subclass thereof).
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*
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* @throws NullPointerException if <code>t</code> is <code>null</code>.
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*/
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public void add(Class t, EventListener listener)
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{
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int oldLength;
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Object[] newList;
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if (listener == null)
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return;
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if (!t.isInstance(listener))
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throw new IllegalArgumentException();
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oldLength = listenerList.length;
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newList = new Object[oldLength + 2];
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if (oldLength > 0)
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System.arraycopy(listenerList, 0, newList, 0, oldLength);
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newList[oldLength] = t;
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newList[oldLength + 1] = listener;
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listenerList = newList;
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}
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/**
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* Determines the number of listeners.
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*/
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public int getListenerCount()
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{
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return listenerList.length / 2;
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}
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/**
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* Determines the number of listeners of a particular class.
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*
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* @param t the type of listeners to be counted. In order to get
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* counted, a subscribed listener must be exactly of class
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* <code>t</code>. Thus, subclasses of <code>t</code> will not be
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* counted.
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*/
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public int getListenerCount(Class t)
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{
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int result = 0;
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for (int i = 0; i < listenerList.length; i += 2)
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if (t == listenerList[i])
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++result;
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return result;
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}
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/**
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* Get a list of listenerType/listener pairs
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* @returns Listener list
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*/
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public Object[] getListenerList()
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{
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return listenerList;
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}
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/**
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* Retrieves the currently subscribed listeners of a particular
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* type. For a listener to be returned, it must have been
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* registered with exactly the type <code>c</code>; subclasses are
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* not considered equal.
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*
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* <p>The returned array can always be cast to <code>c[]</code>.
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* Since it is a newly allocated copy, the caller may arbitrarily
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* modify the array.
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*
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* @param c the class which was passed to {@link #add}.
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*
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* @throws ClassCastException if <code>c</code> does not implement
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* the {@link EventListener} interface.
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*
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* @throws NullPointerException if <code>c</code> is
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* <code>null</code>.
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*
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* @returns an array of <code>c</code> whose elements are the
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* currently subscribed listeners of the specified type. If there
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* are no such listeners, an empty array is returned.
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*
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* @since 1.3
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*/
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public EventListener[] getListeners(Class c)
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{
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int count, f;
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EventListener[] result;
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count = getListenerCount(c);
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result = (EventListener[]) Array.newInstance(c, count);
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f = 0;
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for (int i = 0; i < listenerList.length; i += 2)
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if (listenerList[i] == c)
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result[f++] = (EventListener) listenerList[i + 1];
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return result;
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}
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/**
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* Removes a listener of a specific type.
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*
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* @param t the type of the listener.
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*
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* @param listener the listener to remove, which must be an instance
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* of <code>t</code>, or of a subclass of <code>t</code>.
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*
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* @throws IllegalArgumentException if <code>listener</code> is not
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* an instance of <code>t</code> (or a subclass thereof).
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*
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* @throws NullPointerException if <code>t</code> is <code>null</code>.
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*/
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public void remove(Class t, EventListener listener)
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{
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Object[] oldList, newList;
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int oldLength;
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if (listener == null)
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return;
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if (!t.isInstance(listener))
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throw new IllegalArgumentException();
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oldList = listenerList;
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oldLength = oldList.length;
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for (int i = 0; i < oldLength; i += 2)
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if (oldList[i] == t && oldList[i + 1] == listener)
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{
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if (oldLength == 2)
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newList = NO_LISTENERS;
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else
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{
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newList = new Object[oldLength - 2];
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if (i > 0)
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System.arraycopy(oldList, 0, newList, 0, i);
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if (i < oldLength - 2)
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System.arraycopy(oldList, i + 2, newList, i,
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oldLength - 2 - i);
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}
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listenerList = newList;
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return;
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}
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}
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/**
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* Returns a string representation of this object that may be useful
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* for debugging purposes.
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*/
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public String toString()
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{
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StringBuffer buf = new StringBuffer("EventListenerList: ");
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buf.append(listenerList.length / 2);
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buf.append(" listeners: ");
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for (int i = 0; i < listenerList.length; i += 2)
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{
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buf.append(" type ");
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buf.append(((Class) listenerList[i]).getName());
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buf.append(" listener ");
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buf.append(listenerList[i + 1]);
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}
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return buf.toString();
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}
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}
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