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/*******************************************************************************
* 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;
}
}
}
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