StateEngine


1   /*
2    * @(#)StateEngine.java 1.9 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package com.sun.corba.se.spi.orbutil.fsm;
9   
10  /**
11   * A StateEngine defines the state transition function for a 
12   * finite state machine (FSM). A FSM always has a current state.
13   * In response to an Input, the FSM performs an Action and 
14   * makes a transition to a new state.  Note that any object can
15   * be used as an input if it supports the Input interface.
16   * For example, a protocol message may be an input.  The FSM
17   * uses only the result of calling getLabel on the Input to 
18   * drive the transition.
19   * <p>
20   * The function can be non-deterministic
21   * in that the same input may cause transitions to different new
22   * states from the current state.  In this case, the action that
23   * is executed for the transition must set the correct new state.
24   *
25   * @version @(#)StateEngine.java    1.9 03/12/19
26   * @author Ken Cavanaugh
27   */
28  public interface StateEngine
29  {
30      /** Add a new transition (old,in,guard,act,new) to the state engine.
31      * Multiple calls to add with the same old and in are permitted,
32      * in which case only a transition in which the guard evaluates to
33      * true will be taken.  If no such transition is enabled, a default
34      * will be taken.  If more than one transition is enabled, one will
35      * be chosen arbitrarily.
36      * This method can only be called before done().  An attempt to
37      * call it after done() results in an IllegalStateException.
38      */
39      public StateEngine add( State oldState, Input input, Guard guard, 
40          Action action, State newState ) throws IllegalStateException   ;
41  
42      /** Add a transition with a guard that always evaluates to true.
43      */
44      public StateEngine add( State oldState, Input input, 
45          Action action, State newState ) throws IllegalStateException   ;
46  
47      /** Set the default transition and action for a state.
48      * This transition will be used if no more specific transition was
49      * defined for the actual input.  Repeated calls to this method
50      * simply change the default.
51      * This method can only be called before done().  An attempt to
52      * call it after done() results in an IllegalStateException.
53      */
54      public StateEngine setDefault( State oldState, Action action, State newState )
55          throws IllegalStateException   ;
56  
57      /** Equivalent to setDefault( oldState, act, newState ) where act is an
58       * action that does nothing.
59       */
60      public StateEngine setDefault( State oldState, State newState )
61          throws IllegalStateException   ;
62  
63      /** Euaivalent to setDefault( oldState, oldState ) 
64       */
65      public StateEngine setDefault( State oldState )
66          throws IllegalStateException   ;
67  
68      /** Set the default action used in this state engine.  This is the
69      * action that is called whenever there is no applicable transition.
70      * Normally this would simply flag an error.  This method can only
71      * be called before done().  An attempt to
72      * call it after done() results in an IllegalStateException.
73      */
74      public void setDefaultAction( Action act ) throws IllegalStateException   ;
75  
76      /** Called after all transitions have been added to the state engine.
77      * This provides an opportunity for the implementation to optimize
78      * its representation before the state engine is used.  This method 
79      * may only be called once.  An attempt to call it more than once
80      * results in an IllegalStateException.
81      */
82      public void done() throws IllegalStateException   ;
83  
84      /** Create an instance of a FSM that uses this state engine.
85      * The initial state of the FSM will be the stateState specified
86      * here.  This method can only be called after done().  An attempt
87      * to call it before done results in an IllegalStateException.
88      */
89      public FSM makeFSM( State startState ) throws IllegalStateException   ;
90  }
91  
92  // end of StateEngine.java
93  
94  
95
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