1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 *
19 */
20 package org.apache.mina.statemachine.transition;
21
22 import org.apache.mina.statemachine.State;
23 import org.apache.mina.statemachine.StateMachine;
24 import org.apache.mina.statemachine.event.Event;
25
26 /**
27 * The interface implemented by classes which need to react on transitions
28 * between states.
29 *
30 * A Transition must implement two methods
31 * <ul>
32 * <li>execute : a method called when we process the transition</li>
33 * <li>getNextState : a method that gives the next state for this transition</li>
34 * </ul>
35 *
36 * Each Transition accepts two parameters :
37 * <ul>
38 * <li>An event ID : this defines the event this transition will accept</li>
39 * <li>A next state</li>
40 * </ul>
41 *
42 * The event ID might be '*', which means the transition will accept any event.
43 * The next state can be null, which means teh next state is the current state.
44 *
45 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
46 */
47 public interface Transition {
48 /**
49 * Executes this {@link Transition}. It is the responsibility of this
50 * {@link Transition} to determine whether it actually applies for the
51 * specified {@link Event}. If this {@link Transition} doesn't apply
52 * nothing should be executed and <tt>false</tt> must be returned.
53 * The method will accept any {@link Event} if it is registered with the
54 * wild card event ID ('*'), and the event ID it is declared for (ie,
55 * the event ID that has been passed as a parameter to this transition
56 * constructor.)
57 *
58 * @param event the current {@link Event}.
59 * @return <tt>true</tt> if the {@link Transition} was executed,
60 * <tt>false</tt> otherwise.
61 */
62 boolean execute(Event event);
63
64 /**
65 * @return the {@link State} which the {@link StateMachine} should move to
66 * if this {@link Transition} is taken and {@link #execute(Event)} returns
67 * <tt>true</tt>. <code>null</code> if this {@link Transition} is a loopback
68 * {@link Transition}.
69 */
70 State getNextState();
71 }