/*******************************************************************************
* Copyright (c) 2005, 2006 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.core.commands.common;
import org.eclipse.core.runtime.ListenerList;
/**
* <p>
* A manager to which listeners can be attached. This handles the management of
* a list of listeners -- optimizing memory and performance. All the methods on
* this class are guaranteed to be thread-safe.
* </p>
* <p>
* Clients may extend.
* </p>
*
* @since 3.2
*/
public abstract class EventManager {
/**
* An empty array that can be returned from a call to
* {@link #getListeners()} when {@link #listenerList} is <code>null</code>.
*/
private static final Object[] EMPTY_ARRAY = new Object[0];
/**
* A collection of objects listening to changes to this manager. This
* collection is <code>null</code> if there are no listeners.
*/
private transient ListenerList listenerList = null;
/**
* Adds a listener to this manager that will be notified when this manager's
* state changes.
*
* @param listener
* The listener to be added; must not be <code>null</code>.
*/
protected synchronized final void addListenerObject(final Object listener) {
if (listenerList == null) {
listenerList = new ListenerList(ListenerList.IDENTITY);
}
listenerList.add(listener);
}
/**
* Clears all of the listeners from the listener list.
*/
protected synchronized final void clearListeners() {
if (listenerList != null) {
listenerList.clear();
}
}
/**
* Returns the listeners attached to this event manager.
*
* @return The listeners currently attached; may be empty, but never
* <code>null</code>
*/
protected final Object[] getListeners() {
final ListenerList list = listenerList;
if (list == null) {
return EMPTY_ARRAY;
}
return list.getListeners();
}
/**
* Whether one or more listeners are attached to the manager.
*
* @return <code>true</code> if listeners are attached to the manager;
* <code>false</code> otherwise.
*/
protected final boolean isListenerAttached() {
return listenerList != null;
}
/**
* Removes a listener from this manager.
*
* @param listener
* The listener to be removed; must not be <code>null</code>.
*/
protected synchronized final void removeListenerObject(final Object listener) {
if (listenerList != null) {
listenerList.remove(listener);
if (listenerList.isEmpty()) {
listenerList = null;
}
}
}
}