| /******************************************************************************* |
| * Copyright (c) 2012 Oracle. 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: |
| * Oracle - initial API and implementation |
| ******************************************************************************/ |
| package org.eclipse.jpt.common.utility.command; |
| |
| import java.io.Serializable; |
| import java.util.EventListener; |
| import org.eclipse.jpt.common.utility.internal.StringTools; |
| |
| /** |
| * Extend the repeating command to support listeners that are notified |
| * when an execution "cycle" is complete; i.e. the command has, |
| * for the moment, handled every execution request and quiesced. |
| * This notification is <em>not</em> guaranteed to occur with <em>every</em> |
| * execution "cycle"; since other, unrelated, executions can be triggered |
| * concurrently, causing the "cycle" to continue. |
| * <p> |
| * Provisional API: This interface is part of an interim API that is still |
| * under development and expected to change significantly before reaching |
| * stability. It is available at this early stage to solicit feedback from |
| * pioneering adopters on the understanding that any code that uses this API |
| * will almost certainly be broken (repeatedly) as the API evolves. |
| */ |
| public interface NotifyingRepeatingCommand |
| extends RepeatingCommand |
| { |
| /** |
| * Add the specified listener. |
| */ |
| void addListener(Listener listener); |
| |
| /** |
| * Remove the specified listener. |
| */ |
| void removeListener(Listener listener); |
| |
| |
| // ********** listener ********** |
| |
| /** |
| * Interface implemented by listeners to be notified whenever the |
| * command has quiesced. |
| */ |
| public interface Listener |
| extends EventListener |
| { |
| /** |
| * The specified command has quiesced. |
| */ |
| void executionQuiesced(Command command); |
| } |
| |
| |
| // ********** null singleton ********** |
| |
| /** |
| * Singleton implementation of the notifying repeating command interface |
| * that will do nothing when executed. |
| */ |
| final class Null |
| implements NotifyingRepeatingCommand, Serializable |
| { |
| public static final NotifyingRepeatingCommand INSTANCE = new Null(); |
| public static NotifyingRepeatingCommand instance() { |
| return INSTANCE; |
| } |
| // ensure single instance |
| private Null() { |
| super(); |
| } |
| public void start() { |
| // do nothing |
| } |
| public void execute() { |
| // do nothing |
| } |
| public void stop() { |
| // do nothing |
| } |
| public void addListener(Listener listener) { |
| // do nothing |
| } |
| public void removeListener(Listener listener) { |
| // do nothing |
| } |
| @Override |
| public String toString() { |
| return StringTools.buildSingletonToString(this); |
| } |
| private static final long serialVersionUID = 1L; |
| private Object readResolve() { |
| // replace this object with the singleton |
| return INSTANCE; |
| } |
| } |
| } |