Java tutorial
/* * JBoss, Home of Professional Open Source * Copyright 2005, JBoss Inc., and individual contributors as indicated * by the @authors tag. See the copyright.txt in the distribution for a * full listing of individual contributors. * * This is free software; you can redistribute it and/or modify it * under the terms of the GNU Lesser General Public License as * published by the Free Software Foundation; either version 2.1 of * the License, or (at your option) any later version. * * This software 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 * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this software; if not, write to the Free * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA * 02110-1301 USA, or see the FSF site: http://www.fsf.org. */ import java.util.HashMap; import java.util.HashSet; import java.util.Iterator; import java.util.Map; import java.util.Set; /** * The representation of a finite state machine. * * @author Scott.Stark@jboss.org * @version $Revision: 2787 $ */ @SuppressWarnings("unchecked") public class StateMachine implements Cloneable { /** A description of the state machine */ private String description; /** The set of states making up the state machine */ private HashSet states; /** The starting state */ private State startState; /** The current state of the state machine */ private State currentState; /** * Create a state machine given its states and start state. * * @param states - * Set<State> for the state machine * @param startState - * the starting state */ public StateMachine(Set states, State startState) { this(states, startState, null); } /** * Create a state machine given its states and start state. * * @param states - * Set<State> for the state machine * @param startState - * the starting state * @param description - * an optional description of the state machine */ public StateMachine(Set states, State startState, String description) { this.states = new HashSet(states); this.startState = startState; this.currentState = startState; this.description = description; } /** * Make a copy of the StateMachine maintaining the current state. * * @return a copy of the StateMachine. */ public Object clone() { StateMachine clone = new StateMachine(states, startState, description); clone.currentState = currentState; return clone; } /** * Get the state machine description. * * @return an possibly null description. */ public String getDescription() { return description; } /** * Get the current state of the state machine. * * @return the current state. */ public State getCurrentState() { return currentState; } /** * Get the start state of the state machine. * * @return the start state. */ public State getStartState() { return startState; } /** * Get the states of the state machine. * * @return the machine states. */ public Set getStates() { return states; } /** * Transition to the next state given the name of a valid transition. * * @param actionName - * the name of transition that is valid for the current state. * @return the next state * @throws IllegalTransitionException */ public State nextState(String actionName) throws IllegalTransitionException { Transition t = currentState.getTransition(actionName); if (t == null) { String msg = "No transition for action: '" + actionName + "' from state: '" + currentState.getName() + "'"; throw new IllegalTransitionException(msg); } State nextState = t.getTarget(); System.out.println("nextState(" + actionName + ") = " + nextState); currentState = nextState; return currentState; } /** * Reset the state machine back to the start state * * @return the start state */ public State reset() { this.currentState = startState; return currentState; } public String toString() { StringBuffer tmp = new StringBuffer("StateMachine[:\n"); tmp.append("\tCurrentState: " + currentState.getName()); Iterator i = states.iterator(); while (i.hasNext()) { tmp.append('\n').append(i.next()); } tmp.append(']'); return tmp.toString(); } } /* * JBoss, Home of Professional Open Source Copyright 2005, JBoss Inc., and * individual contributors as indicated by the @authors tag. See the * copyright.txt in the distribution for a full listing of individual * contributors. * * This is free software; you can redistribute it and/or modify it under the * terms of the GNU Lesser General Public License as published by the Free * Software Foundation; either version 2.1 of the License, or (at your option) * any later version. * * This software 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 Lesser General Public License for more * details. * * You should have received a copy of the GNU Lesser General Public License * along with this software; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA, or see the FSF * site: http://www.fsf.org. */ /** * The respresentation of a state in a state machine. * * @author Scott.Stark@jboss.org * @version $Revision: 2787 $ */ @SuppressWarnings("unchecked") class State { /** The name of the state */ private String name; /** HashMap<String, Transition> */ private HashMap allowedTransitions = new HashMap(); /** Arbitrary state data */ private Object data; public State(String name) { this(name, null); } public State(String name, Map transitions) { this.name = name; if (transitions != null) { allowedTransitions.putAll(transitions); } } /** * Get the state name. * * @return the name of the state. */ public String getName() { return name; } public Object getData() { return data; } public void setData(Object data) { this.data = data; } /** * An accept state is indicated by no transitions * * @return true if this is an accept state, false otherwise. */ public boolean isAcceptState() { return allowedTransitions.size() == 0; } /** * Add a transition to the allowed transition map. * * @param transition * @return this to allow chained addTransition calls */ public State addTransition(Transition transition) { allowedTransitions.put(transition.getName(), transition); return this; } /** * Lookup an allowed transition given its name. * * @param name - * the name of a valid transition from this state. * @return the valid transition if it exists, null otherwise. */ public Transition getTransition(String name) { Transition t = (Transition) allowedTransitions.get(name); return t; } /** * Get the Map<String, Transition> of allowed transitions for this state. * * @return the allowed transitions map. */ public Map getTransitions() { return allowedTransitions; } public String toString() { StringBuffer tmp = new StringBuffer("State(name="); tmp.append(name); Iterator i = allowedTransitions.entrySet().iterator(); while (i.hasNext()) { Map.Entry e = (Map.Entry) i.next(); tmp.append("\n\t on: "); tmp.append(e.getKey()); Transition t = (Transition) e.getValue(); tmp.append(" go to: "); tmp.append(t.getTarget().getName()); } tmp.append(')'); return tmp.toString(); } } /* * JBoss, Home of Professional Open Source Copyright 2005, JBoss Inc., and * individual contributors as indicated by the @authors tag. See the * copyright.txt in the distribution for a full listing of individual * contributors. * * This is free software; you can redistribute it and/or modify it under the * terms of the GNU Lesser General Public License as published by the Free * Software Foundation; either version 2.1 of the License, or (at your option) * any later version. * * This software 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 Lesser General Public License for more * details. * * You should have received a copy of the GNU Lesser General Public License * along with this software; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA, or see the FSF * site: http://www.fsf.org. */ /** * A representation of a transition from a state to another state. * * @author Scott.Stark@jboss.org * @version $Revision: 1958 $ */ class Transition { private String name; private State target; public Transition(String name, State target) { this.name = name; this.target = target; } public String getName() { return name; } public State getTarget() { return target; } } /* * JBoss, Home of Professional Open Source Copyright 2005, JBoss Inc., and * individual contributors as indicated by the @authors tag. See the * copyright.txt in the distribution for a full listing of individual * contributors. * * This is free software; you can redistribute it and/or modify it under the * terms of the GNU Lesser General Public License as published by the Free * Software Foundation; either version 2.1 of the License, or (at your option) * any later version. * * This software 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 Lesser General Public License for more * details. * * You should have received a copy of the GNU Lesser General Public License * along with this software; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA, or see the FSF * site: http://www.fsf.org. */ /** * An exception thrown when an invalid transition is attempted from a state. * * @author Scott.Stark@jboss.org * @version $Revision: 2800 $ */ class IllegalTransitionException extends Exception { /** The serialVersionUID */ private static final long serialVersionUID = -3392564168782896452L; public IllegalTransitionException(String msg) { super(msg); } }