001/* A pair of states.
002
003 Copyright (c) 1999-2014 The Regents of the University of California.
004 All rights reserved.
005 Permission is hereby granted, without written agreement and without
006 license or royalty fees, to use, copy, modify, and distribute this
007 software and its documentation for any purpose, provided that the above
008 copyright notice and the following two paragraphs appear in all copies
009 of this software.
010
011 IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
012 FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
013 ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
014 THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF
015 SUCH DAMAGE.
016
017 THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
018 INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
019 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
020 PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
021 CALIFORNIA HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES,
022 ENHANCEMENTS, OR MODIFICATIONS.
023
024 PT_COPYRIGHT_VERSION_2
025 COPYRIGHTENDKEY
026 */
027package ptolemy.domains.modal.kernel.ia;
028
029import ptolemy.domains.modal.kernel.State;
030
031///////////////////////////////////////////////////////////////////
032//// StatePair
033
034/**
035 A pair of states.
036 This class is used in the representation of alternating simulation.
037 @see InterfaceAutomaton#computeAlternatingSimulation
038
039 @author Yuhong Xiong
040 @version $Id$
041 @since Ptolemy II 8.0
042 @Pt.ProposedRating Red (yuhong)
043 @Pt.AcceptedRating Red (yuhong)
044 */
045public class StatePair {
046    /** Construct an instance with the specified states.
047     *  @param first The first state in the pair.
048     *  @param second The second state in the pair.
049     */
050    public StatePair(State first, State second) {
051        _first = first;
052        _second = second;
053    }
054
055    ///////////////////////////////////////////////////////////////////
056    ////                         public methods                    ////
057
058    /** Override the base class method to return true if the specified
059     *  object is an instance of StatePair and it contains the same
060     *  states as this one.
061     *  @param object An object to compare with this one.
062     *  @return True if the specified object is an instance of StatePair
063     *   and this one contains the same states, false otherwise.
064     */
065    @Override
066    public boolean equals(Object object) {
067        if (object instanceof StatePair) {
068            return this.first() == ((StatePair) object).first()
069                    && this.second() == ((StatePair) object).second();
070        }
071
072        return false;
073    }
074
075    /** Return the first state in this pair.
076     *  @return The first state in this pair.
077     */
078    public State first() {
079        return _first;
080    }
081
082    /** Override the base class method to ensure that the pairs that
083     *  are equal (according to the equals() method) have the same
084     *  hash code.
085     *  @return The hash code.
086     */
087    @Override
088    public int hashCode() {
089        return _first.hashCode() + _second.hashCode();
090    }
091
092    /** Return the second state in this pair.
093     *  @return The second state in this pair.
094     */
095    public State second() {
096        return _second;
097    }
098
099    /** Return a string representation of this pair. The string contains
100     *  the name of the first state, followed by a " - ", followed by
101     *  the name of the second state.
102     *  @return A string containing the names of the two states separated
103     *   by a " - ".
104     */
105    @Override
106    public String toString() {
107        return _first.getName() + " - " + _second.getName();
108    }
109
110    ///////////////////////////////////////////////////////////////////
111    ////                         private variables                 ////
112    private State _first;
113
114    private State _second;
115}