Package pygar.state

Class StateMachine<T>

java.lang.Object
java.util.Observable
pygar.state.StateMachine<T>
Type Parameters:
T - the type of the context object that accompanies each event
Direct Known Subclasses:
NegotiationGroupStateMachine, OrderedStateMachine, PmessageStateMachine
@ThreadSafe
public class StateMachine<T>
extends java.util.Observable
This class implements simple state machines that respond to events. The events are named and contain context information of type T. State machines have predefined transitions. Each transition is characterized by a start state, an end state, the action that provokes the transition and an event handle that performs any associated action.

Several sub-types of transitions are supported. If an event has no particular starting state, then the transition may be specified with a null starting state. Such transitions may have a defined list of starting states that should not respond to the event.

A transition may have a null end state. This transition is interpreted as a loop-back - a state that performs the eventHandler and returns to the same state.

Each statemachine has two optional slots that support a simple persistence scheme that can be used to checkpoint and rollback the system. The first slot contains a persistence id. The second contains function object for logging transitions. (optional slots not currently implemented)

  • Nested Class Summary

    Nested Classes 
    Modifier and Type Class Description
    class  StateMachine.Context
    Class Context defines the data for observers of this state machine.
    class  StateMachine.TransitionPt1
    This inner class contains a lookup table for events
    class  StateMachine.TransitionPt2
    transition description
    class  StateMachine.TransitionPt3
    alternate transition description for transitions that have many starting states.

  • Constructor Summary

    Constructors 
    Constructor Description
    StateMachine​(java.lang.String start)  

  • Method Summary

    Modifier and Type Method Description
    protected StateMachine.Context _getStateContext()
    Internal routine called from a super class to create a copy of context as it is known to this class.
    void acceptContextFreeEvent​(java.lang.String event)
    Receive an event from another object with no context specified.
    void acceptEvent​(java.lang.String event, T context)
    Receive an event from another object in the context of a third context object of type T.
    void addTransition​(java.lang.String startState, java.lang.String eventName, java.lang.String endState, EventListener<T> action)
    Add a transition to the state machine where the transition has a definite start state.
    void addTransition​(java.lang.String eventName, java.lang.String endState, EventListener<T> action, java.lang.String[] insensitive)
    Add a transition to the state machine where the transition has multiple start states.
    java.lang.String getState()
    Return the current state of the state machine.
    static void main​(java.lang.String[] args)  
    void notifyObservers()
    Function to perform the duties of an observable n.b.
    void notifyObservers​(java.lang.Object o)  
    void setState​(java.lang.String state)
    Assign a state to the state machine.

    Methods inherited from class java.util.Observable

    addObserver, clearChanged, countObservers, deleteObserver, deleteObservers, hasChanged, setChanged

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • StateMachine

      public StateMachine​(java.lang.String start)

  • Method Details

    • notifyObservers

      public void notifyObservers()
      Function to perform the duties of an observable n.b. all the callers of this procedure should synchronize on "this"
      Overrides:
      notifyObservers in class java.util.Observable

    • notifyObservers

      public void notifyObservers​(java.lang.Object o)
      Overrides:
      notifyObservers in class java.util.Observable

    • _getStateContext

      protected StateMachine.Context _getStateContext()
      Internal routine called from a super class to create a copy of context as it is known to this class. The message field is left blank for completion later.
      Returns:
      Context

    • setState

      public void setState​(java.lang.String state)
      Assign a state to the state machine. Normally, however, you should just let that events induce state transitions.
      Parameters:
      state -

    • getState

      public java.lang.String getState()
      Return the current state of the state machine.
      Returns:
      state

    • addTransition

      public void addTransition​(java.lang.String eventName, java.lang.String endState, EventListener<T> action, java.lang.String[] insensitive)
      Add a transition to the state machine where the transition has multiple start states.
      Parameters:
      eventName - name of the event
      endState - state after the event or null if this is a loop-back
      action - EventListener that provides actions for the transition
      insensitive - a list of start state names that do not respond to this event

    • addTransition

      public void addTransition​(java.lang.String startState, java.lang.String eventName, java.lang.String endState, EventListener<T> action)
      Add a transition to the state machine where the transition has a definite start state.
      Parameters:
      startState - initial state of transition or null for an event operating on all states.
      eventName - name of the event
      endState - state after the event or null if this is a loop-back
      action - EventListener that provides actions for the transition

    • acceptContextFreeEvent

      public void acceptContextFreeEvent​(java.lang.String event) throws MessageSystemException, java.lang.InterruptedException, java.lang.reflect.InvocationTargetException
      Receive an event from another object with no context specified. N.b. the success of the operation depends on the handlers for the transition invoked by the event. If the handler, requires a context, then the operation fails. Context free events are usually associated with user input events, not enterprise messages.
      Parameters:
      event -
      Throws:
      MessageSystemException
      java.lang.InterruptedException
      java.lang.reflect.InvocationTargetException

    • acceptEvent

      public void acceptEvent​(java.lang.String event, T context) throws java.lang.Exception
      Receive an event from another object in the context of a third context object of type T.
      Parameters:
      event -
      context -
      Throws:
      java.lang.Exception

    • main

      public static void main​(java.lang.String[] args)
      Parameters:
      args -