001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License.
018 *
019 */
020package org.apache.mina.statemachine.transition;
021
022import org.apache.mina.statemachine.State;
023import org.apache.mina.statemachine.StateMachine;
024import org.apache.mina.statemachine.event.Event;
025
026/**
027 * The interface implemented by classes which need to react on transitions
028 * between states.
029 *
030 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
031 */
032public interface Transition {
033    /**
034     * Executes this {@link Transition}. It is the responsibility of this
035     * {@link Transition} to determine whether it actually applies for the
036     * specified {@link Event}. If this {@link Transition} doesn't apply
037     * nothing should be executed and <tt>false</tt> must be returned.
038     * 
039     * @param event the current {@link Event}.
040     * @return <tt>true</tt> if the {@link Transition} was executed, 
041     *         <tt>false</tt> otherwise.
042     */
043    boolean execute(Event event);
044
045    /**
046     * @return the {@link State} which the {@link StateMachine} should move to 
047     * if this {@link Transition} is taken and {@link #execute(Event)} returns
048     * <tt>true</tt>. <code>null</code> if this {@link Transition} is a loopback 
049     * {@link Transition}.
050     */
051    State getNextState();
052}