| /******************************************************************************* |
| * 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 org.eclipse.jpt.common.utility.internal.StringTools; |
| |
| /** |
| * This command will execute repeatedly the minimum |
| * number of times. The assumption is the command's effects are |
| * cumulative(?); i.e. the cumulative result of multiple executions of the |
| * command is no different than the result of a single execution of the command. |
| * Once the command is executing, any further requests to execute simply trigger |
| * a re-execution of the command once it has finished its current execution. |
| * <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 RepeatingCommand |
| extends Command |
| { |
| /** |
| * Start the command, allowing it to begin executing with the next call to |
| * {@link #execute()}. |
| * @exception IllegalStateException when the command is not stopped |
| */ |
| void start(); |
| |
| /** |
| * Stop the command; ignore further calls to {@link #execute()}. |
| * @exception IllegalStateException when the command executor is not started |
| */ |
| void stop() throws InterruptedException; |
| |
| |
| /** |
| * Singleton implementation of the repeating command interface that will do |
| * nothing when executed. |
| */ |
| final class Null |
| implements RepeatingCommand, Serializable |
| { |
| public static final RepeatingCommand INSTANCE = new Null(); |
| public static RepeatingCommand instance() { |
| return INSTANCE; |
| } |
| // ensure single instance |
| private Null() { |
| super(); |
| } |
| public void start() { |
| // do nothing |
| } |
| public void execute() { |
| // do nothing |
| } |
| public void stop() { |
| // 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; |
| } |
| } |
| } |