// Prevayler(TM) - The Open-Source Prevalence Layer.
// Copyright (C) 2001 Klaus Wuestefeld.
// This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License version 2.1 as published by the Free Software Foundation. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.

package org.prevayler;

import java.io.Serializable;

 * An atomic transaction to be executed on a PrevalentSystem. Any operation which changes the observable state of a PrevalentSystem must be encapsulated as a Command.
public interface Command extends Serializable {

   * Executes this command on the received system. See org.prevayler.demos for examples. The returned object has to be Serializable in preparation for future versions of Prevayler that will provide fault-tolerance through system replicas.
   * @return The object returned by the execution of this command. Most commands simply return null.
  public Serializable execute(PrevalentSystem system) throws Throwable;