path: root/javax/swing/event/EventListenerList.java

/* EventListenerList.java --
   Copyright (C) 2002, 2004, 2005, 2006,  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.

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General Public License for more details.

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along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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this exception to your version of the library, but you are not
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package javax.swing.event;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.EventListener;


/**
 * A utility class for keeping track of {@link EventListener}s.
 *
 * <p><b>Example for using this class:</b>
 *
 * <blockquote><pre> import java.util.EventListener;
 * import javax.swing.event.EventListenerList;
 *
 * class Foo
 * {
 *   protected final EventListenerList listeners = new EventListenerList();
 *   protected BarClosedEvent barClosedEvent = null;
 *
 *   public void addBarListener(BarListener l)
 *   {
 *     listeners.<a href="#add(java.lang.Class, java.util.EventListener)"
 *               >add</a>(BarListener.class, l);
 *   }
 *
 *   public void removeBarListener(BarListener l)
 *   {
 *     listeners.<a href="#remove(java.lang.Class, java.util.EventListener)"
 *               >remove</a>(BarListener.class, l);
 *   }
 *
 *   protected void fireBarClosedEvent()
 *   {
 *     Object[] l = listeners.<a href="#getListenerList()"
 *                            >getListenerList()</a>;
 *
 *     for (int i = l.length - 2; i >= 0; i -= 2)
 *       if (l[i] == BarListener.class)
 *         {
 *           // Create the event on demand, when it is needed the first time.
 *           if (barClosedEvent == null)
 *             barClosedEvent = new BarClosedEvent(this);
 *
 *           ((BarClosedListener) l[i + 1]).barClosed(barClosedEvent);
 *         }
 *   }
 * }</pre></blockquote>
 *
 * @author Andrew Selkirk (aselkirk@sympatico.ca)
 * @author Sascha Brawer (brawer@dandelis.ch)
 */
public class EventListenerList
  implements Serializable
{
  /**
   * An ID for serializing instances of this class; verified with the
   * serialver tool of Sun J2SE 1.4.1_01.
   */
  static final long serialVersionUID = -5677132037850737084L;


  /**
   * An empty array that is shared by all instances of this class that
   * have no listeners.
   */
  private static final Object[] NO_LISTENERS = new Object[0];
  
  
  /**
   * An array with all currently registered listeners.  The array has
   * twice as many elements as there are listeners.  For an even
   * integer <code>i</code>, <code>listenerList[i]</code> indicates
   * the registered class, and <code>listenerList[i + 1]</code> is the
   * listener.
   */
  protected transient Object[] listenerList = NO_LISTENERS;

  
  /**
   * EventListenerList constructor
   */
  public EventListenerList()
  {
    // Nothing to do here.
  }


  /**
   * Registers a listener of a specific type.
   *
   * @param t the type of the listener.
   *
   * @param listener the listener to add, which must be an instance of
   * <code>t</code>, or of a subclass of <code>t</code>.
   *
   * @throws IllegalArgumentException if <code>listener</code> is not
   * an instance of <code>t</code> (or a subclass thereof).
   *
   * @throws NullPointerException if <code>t</code> is <code>null</code>.
   */
  public <T extends EventListener> void add(Class<T> t, T listener)
  {
    int oldLength;
    Object[] newList;

    if (listener == null)
      return;

    if (!t.isInstance(listener))
      throw new IllegalArgumentException();

    oldLength = listenerList.length;
    newList = new Object[oldLength + 2];
    if (oldLength > 0)
      System.arraycopy(listenerList, 0, newList, 0, oldLength);

    newList[oldLength] = t;
    newList[oldLength + 1] = listener;
    listenerList = newList;
  }


  /**
   * Determines the number of listeners.
   */
  public int getListenerCount()
  {
    return listenerList.length / 2;
  }


  /**
   * Determines the number of listeners of a particular class.
   *
   * @param t the type of listeners to be counted. In order to get
   * counted, a subscribed listener must be exactly of class
   * <code>t</code>. Thus, subclasses of <code>t</code> will not be
   * counted.
   */
  public int getListenerCount(Class<?> t)
  {
    int result = 0;
    for (int i = 0; i < listenerList.length; i += 2)
      if (t == listenerList[i])
        ++result;

    return result;
  }


  /**
   * Returns an array containing a sequence of listenerType/listener pairs, one
   * for each listener.
   * 
   * @return An array containing the listener types and references.
   */
  public Object[] getListenerList()
  {
    // returning the internal storage is a bad idea, but tests show that the
    // reference implementation does this...
    return listenerList;
  }


  /**
   * Retrieves the currently subscribed listeners of a particular
   * type.  For a listener to be returned, it must have been
   * registered with exactly the type <code>c</code>; subclasses are
   * not considered equal.
   *
   * <p>The returned array can always be cast to <code>c[]</code>.
   * Since it is a newly allocated copy, the caller may arbitrarily
   * modify the array.
   *
   * @param c the class which was passed to {@link #add}.
   *
   * @throws ClassCastException if <code>c</code> does not implement
   * the {@link EventListener} interface.
   *
   * @throws NullPointerException if <code>c</code> is
   * <code>null</code>.
   *
   * @return an array of <code>c</code> whose elements are the
   * currently subscribed listeners of the specified type.  If there
   * are no such listeners, an empty array is returned.
   *
   * @since 1.3
   */
  public <T extends EventListener> T[] getListeners(Class<T> c)
  {
    int count, f;
    EventListener[] result;

    count = getListenerCount(c);
    result = (EventListener[]) Array.newInstance(c, count);
    f = 0;
    for (int i = listenerList.length - 2; i >= 0; i -= 2)
      if (listenerList[i] == c)
        result[f++] = (EventListener) listenerList[i + 1];
    
    return (T[]) result;
  }


  /**
   * Removes a listener of a specific type.
   *
   * @param t the type of the listener.
   *
   * @param listener the listener to remove, which must be an instance
   * of <code>t</code>, or of a subclass of <code>t</code>.
   *
   * @throws IllegalArgumentException if <code>listener</code> is not
   * an instance of <code>t</code> (or a subclass thereof).
   *
   * @throws NullPointerException if <code>t</code> is <code>null</code>.
   */
  public <T extends EventListener> void remove(Class<T> t, T listener)
  {
    Object[] oldList, newList;
    int oldLength;

    if (listener == null)
      return;

    if (!t.isInstance(listener))
      throw new IllegalArgumentException();

    oldList = listenerList;
    oldLength = oldList.length;
    for (int i = 0; i < oldLength; i += 2)
      if (oldList[i] == t && oldList[i + 1] == listener)
        {
          if (oldLength == 2)
            newList = NO_LISTENERS;
          else
            {
              newList = new Object[oldLength - 2];
              if (i > 0)
                System.arraycopy(oldList, 0, newList, 0, i);
              if (i < oldLength - 2)
                System.arraycopy(oldList, i + 2, newList, i,
                                 oldLength - 2 - i);
            }
          listenerList = newList;
          return;
        }
  }


  /**
   * Returns a string representation of this object that may be useful
   * for debugging purposes.
   */
  public String toString()
  {
    StringBuffer buf = new StringBuffer("EventListenerList: ");
    buf.append(listenerList.length / 2);
    buf.append(" listeners: ");
    for (int i = 0; i < listenerList.length; i += 2)
      {
        buf.append(" type ");
        buf.append(((Class) listenerList[i]).getName());
        buf.append(" listener ");
        buf.append(listenerList[i + 1]);
      }
    return buf.toString();
  }

  /**
   * Serializes an instance to an ObjectOutputStream.
   *
   * @param out the stream to serialize to
   *
   * @throws IOException if something goes wrong
   */
  private void writeObject(ObjectOutputStream out)
    throws IOException
  {
    out.defaultWriteObject();
    for (int i = 0; i < listenerList.length; i += 2)
      {
        Class cl = (Class) listenerList[i];
        EventListener l = (EventListener) listenerList[i + 1];
        if (l != null && l instanceof Serializable)
          {
            out.writeObject(cl.getName());
            out.writeObject(l);
          }
      }
    // Write end marker.
    out.writeObject(null);
  }

  /**
   * Deserializes an instance from an ObjectInputStream.
   *
   * @param in the input stream
   *
   * @throws ClassNotFoundException if a serialized class can't be found
   * @throws IOException if something goes wrong
   */
  private <T extends EventListener> void readObject(ObjectInputStream in)
    throws ClassNotFoundException, IOException
  {
    listenerList = NO_LISTENERS;
    in.defaultReadObject();
    Object type;
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    while ((type = in.readObject()) != null)
      {
        EventListener l = (EventListener) in.readObject();
        add(((Class<T>) Class.forName((String) type, true, cl)), (T) l);
      }
  }
}