StateEngine.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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package org.jboss.com.sun.corba.se.spi.orbutil.fsm;

/**
 * A StateEngine defines the state transition function for a finite state machine (FSM). A FSM always has a current
 * state. In response to an Input, the FSM performs an Action and makes a transition to a new state. Note that any
 * object can be used as an input if it supports the Input interface. For example, a protocol message may be an input.
 * The FSM uses only the result of calling getLabel on the Input to drive the transition.
 * <p>
 * The function can be non-deterministic in that the same input may cause transitions to different new states from the
 * current state. In this case, the action that is executed for the transition must set the correct new state.
 * 
 * @author Ken Cavanaugh
 */
public interface StateEngine
{
    /**
     * Add a new transition (old,in,guard,act,new) to the state engine. Multiple calls to add with the same old and in
     * are permitted, in which case only a transition in which the guard evaluates to true will be taken. If no such
     * transition is enabled, a default will be taken. If more than one transition is enabled, one will be chosen
     * arbitrarily. This method can only be called before done(). An attempt to call it after done() results in an
     * IllegalStateException.
     */
    public StateEngine add(State oldState, Input input, Guard guard, Action action, State newState)
            throws IllegalStateException;

    /**
     * Add a transition with a guard that always evaluates to true.
     */
    public StateEngine add(State oldState, Input input, Action action, State newState) throws IllegalStateException;

    /**
     * Set the default transition and action for a state. This transition will be used if no more specific transition
     * was defined for the actual input. Repeated calls to this method simply change the default. This method can only
     * be called before done(). An attempt to call it after done() results in an IllegalStateException.
     */
    public StateEngine setDefault(State oldState, Action action, State newState) throws IllegalStateException;

    /**
     * Equivalent to setDefault( oldState, act, newState ) where act is an action that does nothing.
     */
    public StateEngine setDefault(State oldState, State newState) throws IllegalStateException;

    /**
     * Euaivalent to setDefault( oldState, oldState )
     */
    public StateEngine setDefault(State oldState) throws IllegalStateException;

    /**
     * Set the default action used in this state engine. This is the action that is called whenever there is no
     * applicable transition. Normally this would simply flag an error. This method can only be called before done(). An
     * attempt to call it after done() results in an IllegalStateException.
     */
    public void setDefaultAction(Action act) throws IllegalStateException;

    /**
     * Called after all transitions have been added to the state engine. This provides an opportunity for the
     * implementation to optimize its representation before the state engine is used. This method may only be called
     * once. An attempt to call it more than once results in an IllegalStateException.
     */
    public void done() throws IllegalStateException;

    /**
     * Create an instance of a FSM that uses this state engine. The initial state of the FSM will be the stateState
     * specified here. This method can only be called after done(). An attempt to call it before done results in an
     * IllegalStateException.
     */
    public FSM makeFSM(State startState) throws IllegalStateException;
}

// end of StateEngine.java