| /******************************************************************************* |
| * Copyright (c) 2007, 2009 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; |
| |
| import java.io.Serializable; |
| |
| /** |
| * Simple interface for implementing the GOF Command design pattern, |
| * and it doesn't carry the baggage of {@link java.lang.Runnable}. |
| * <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 Command { |
| |
| /** |
| * Execute the command. The semantics of the command |
| * is determined by the contract between the client and server. |
| */ |
| void execute(); |
| |
| /** |
| * Singleton implementation of the command interface that will do nothing |
| * when executed. |
| */ |
| final class Null implements Command, Serializable { |
| public static final Command INSTANCE = new Null(); |
| public static Command instance() { |
| return INSTANCE; |
| } |
| // ensure single instance |
| private Null() { |
| super(); |
| } |
| public void execute() { |
| // do nothing |
| } |
| @Override |
| public String toString() { |
| return "Command.Null"; //$NON-NLS-1$ |
| } |
| private static final long serialVersionUID = 1L; |
| private Object readResolve() { |
| // replace this object with the singleton |
| return INSTANCE; |
| } |
| } |
| |
| /** |
| * Singleton implementation of the command interface that will throw an |
| * exception when executed. |
| */ |
| final class Disabled implements Command, Serializable { |
| public static final Command INSTANCE = new Disabled(); |
| public static Command instance() { |
| return INSTANCE; |
| } |
| // ensure single instance |
| private Disabled() { |
| super(); |
| } |
| // throw an exception |
| public void execute() { |
| throw new UnsupportedOperationException(); |
| } |
| @Override |
| public String toString() { |
| return "Command.Disabled"; //$NON-NLS-1$ |
| } |
| private static final long serialVersionUID = 1L; |
| private Object readResolve() { |
| // replace this object with the singleton |
| return INSTANCE; |
| } |
| } |
| |
| } |