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 * Abstract {@link Transition} implementation. Takes care of matching the
028 * current {@link Event}'s id against the id of the {@link Event} this 
029 * {@link Transition} handles. To handle any {@link Event} the id should be set
030 * to {@link Event#WILDCARD_EVENT_ID}.
031 *
032 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
033 */
034public abstract class AbstractTransition implements Transition {
035    private final Object eventId;
036
037    private final State nextState;
038
039    /**
040     * Creates a new instance which will loopback to the same {@link State} 
041     * for the specified {@link Event} id.
042     * 
043     * @param eventId the {@link Event} id.
044     */
045    public AbstractTransition(Object eventId) {
046        this(eventId, null);
047    }
048
049    /**
050     * Creates a new instance with the specified {@link State} as next state 
051     * and for the specified {@link Event} id.
052     * 
053     * @param eventId the {@link Event} id.
054     * @param nextState the next {@link State}.
055     */
056    public AbstractTransition(Object eventId, State nextState) {
057        this.eventId = eventId;
058        this.nextState = nextState;
059    }
060
061    public State getNextState() {
062        return nextState;
063    }
064
065    public boolean execute(Event event) {
066        if (!eventId.equals(Event.WILDCARD_EVENT_ID) && !eventId.equals(event.getId())) {
067            return false;
068        }
069
070        return doExecute(event);
071    }
072
073    /**
074     * Executes this {@link Transition}. This method doesn't have to check
075     * if the {@link Event}'s id matches because {@link #execute(Event)} has
076     * already made sure that that is the case.
077     * 
078     * @param event the current {@link Event}.
079     * @return <tt>true</tt> if the {@link Transition} has been executed 
080     *         successfully and the {@link StateMachine} should move to the 
081     *         next {@link State}. <tt>false</tt> otherwise.
082     */
083    protected abstract boolean doExecute(Event event);
084
085    public boolean equals(Object o) {
086        if (o == this) {
087            return true;
088        }
089
090        if (!(o instanceof AbstractTransition)) {
091            return false;
092        }
093        
094        AbstractTransition that = (AbstractTransition) o;
095        
096        if (eventId != null) {
097            if (!eventId.equals( that.eventId )) {
098                return false;
099            }
100        } else {
101            if (that.eventId != null) {
102                return false;
103            }
104        }
105        
106        
107        if (nextState != null) {
108            return nextState.equals( that.nextState );
109        } else {
110            return that.nextState == null;
111        }
112    }
113
114    public int hashCode() {
115        int h = 17;
116        
117        if ( eventId != null) {
118            h = h*37 + eventId.hashCode();
119        }
120        
121        if (nextState != null) {
122            h = h*17 + nextState.hashCode();
123        }
124        
125        return h;
126    }
127
128    public String toString() {
129        StringBuilder sb = new StringBuilder();
130        
131        sb.append("eventId=").append(eventId);
132        sb.append(",nextState=").append(nextState);
133        return sb.toString();
134    }
135}