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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   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
31   */
32  public interface Transition {
33      /**
34       * Executes this {@link Transition}. It is the responsibility of this
35       * {@link Transition} to determine whether it actually applies for the
36       * specified {@link Event}. If this {@link Transition} doesn't apply
37       * nothing should be executed and <tt>false</tt> must be returned.
38       * 
39       * @param event the current {@link Event}.
40       * @return <tt>true</tt> if the {@link Transition} was executed, 
41       *         <tt>false</tt> otherwise.
42       */
43      boolean execute(Event event);
44  
45      /**
46       * @return the {@link State} which the {@link StateMachine} should move to 
47       * if this {@link Transition} is taken and {@link #execute(Event)} returns
48       * <tt>true</tt>. <code>null</code> if this {@link Transition} is a loopback 
49       * {@link Transition}.
50       */
51      State getNextState();
52  }