| /******************************************************************************* |
| * Copyright (c) 2003, 2005 IBM Corporation and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| /* |
| |
| |
| */ |
| package org.eclipse.jem.internal.proxy.core; |
| |
| /** |
| * This class is used to maintain a list of listeners, and |
| * is used in the implementations of several classes within jem |
| * which allow you to register listeners of various kinds. |
| * It is a fairly lightweight object, occupying minimal space when |
| * no listeners are registered. |
| * <p> |
| * Note that the <code>add</code> method checks for and eliminates |
| * duplicates based on identity (not equality). Likewise, the |
| * <code>remove</code> method compares based on identity. |
| * </p> |
| * <p> |
| * Use the <code>getListeners</code> method when notifying listeners. |
| * Note that no garbage is created if no listeners are registered. |
| * The recommended code sequence for notifying all registered listeners |
| * of say, <code>FooListener.eventHappened</code>, is: |
| * <pre> |
| * Object[] listeners = myListenerList.getListeners(); |
| * for (int i = 0; i < listeners.length; ++i) { |
| * ((FooListener) listeners[i]).eventHappened(event); |
| * } |
| * </pre> |
| * </p> |
| */ |
| |
| public class ListenerList { |
| |
| /** |
| * The initial capacity of the list. Always >= 1. |
| */ |
| private int capacity; |
| |
| /** |
| * The current number of listeners. |
| * Maintains invariant: 0 <= size <= listeners.length. |
| */ |
| private int size; |
| |
| /** |
| * The list of listeners. Initially <code>null</code> but initialized |
| * to an array of size capacity the first time a listener is added. |
| * Maintains invariant: listeners != null IFF size != 0 |
| */ |
| private Object[] listeners = null; |
| |
| /** |
| * The empty array singleton instance, returned by getListeners() |
| * when size == 0. |
| */ |
| private static final Object[] EmptyArray = new Object[0]; |
| |
| /** |
| * Creates a listener list with an initial capacity of 1. |
| */ |
| public ListenerList() { |
| this(1); |
| } |
| |
| /** |
| * Creates a listener list with the given initial capacity. |
| * |
| * @param capacity the number of listeners which this list can initially accept |
| * without growing its internal representation; must be at least 1 |
| */ |
| public ListenerList(int capacity) { |
| if (!(capacity >= 1)) |
| throw new IllegalArgumentException(); |
| this.capacity = capacity; |
| } |
| |
| /** |
| * Adds the given listener to this list. Has no effect if an identical listener |
| * is already registered. |
| * |
| * @param listener the listener |
| */ |
| public void add(Object listener) { |
| if (listener == null) |
| throw new IllegalArgumentException(); |
| if (size == 0) { |
| listeners = new Object[capacity]; |
| } else { |
| // check for duplicates using identity |
| for (int i = 0; i < size; ++i) { |
| if (listeners[i] == listener) { |
| return; |
| } |
| } |
| // grow array if necessary |
| if (size == listeners.length) { |
| System.arraycopy( |
| listeners, |
| 0, |
| listeners = new Object[size * 2 + 1], |
| 0, |
| size); |
| } |
| } |
| listeners[size++] = listener; |
| } |
| |
| /** |
| * Removes all listeners from this list. |
| */ |
| public void clear() { |
| size = 0; |
| listeners = null; |
| } |
| |
| /** |
| * Returns an array containing all the registered listeners, |
| * in the order in which they were added. |
| * <p> |
| * The resulting array is unaffected by subsequent adds or removes. |
| * If there are no listeners registered, the result is an empty array |
| * singleton instance (no garbage is created). |
| * Use this method when notifying listeners, so that any modifications |
| * to the listener list during the notification will have no effect on the |
| * notification itself. |
| * </p> |
| * |
| * @return the list of registered listeners |
| */ |
| public Object[] getListeners() { |
| if (size == 0) |
| return EmptyArray; |
| Object[] result = new Object[size]; |
| System.arraycopy(listeners, 0, result, 0, size); |
| return result; |
| } |
| |
| /** |
| * Returns whether this listener list is empty. |
| * |
| * @return <code>true</code> if there are no registered listeners, and |
| * <code>false</code> otherwise |
| */ |
| public boolean isEmpty() { |
| return size == 0; |
| } |
| |
| /** |
| * Removes the given listener from this list. Has no effect if an identical |
| * listener was not already registered. |
| * |
| * @param listener the listener |
| */ |
| public void remove(Object listener) { |
| if (listener == null) |
| throw new IllegalArgumentException(); |
| for (int i = 0; i < size; ++i) { |
| if (listeners[i] == listener) { |
| if (size == 1) { |
| listeners = null; |
| size = 0; |
| } else { |
| System.arraycopy( |
| listeners, |
| i + 1, |
| listeners, |
| i, |
| --size - i); |
| listeners[size] = null; |
| } |
| return; |
| } |
| } |
| } |
| |
| /** |
| * Returns the number of registered listeners. |
| * |
| * @return the number of registered listeners |
| */ |
| public int size() { |
| return size; |
| } |
| |
| } |