001package net.sf.cpsolver.ifs.model;
002
003/**
004 * Binary constraint. <br>
005 * <br>
006 * Extension of {@link Constraint} that links exactly two variables.
007 * 
008 * @see Variable
009 * @see Constraint
010 * @see Model
011 * 
012 * @version IFS 1.2 (Iterative Forward Search)<br>
013 *          Copyright (C) 2006 - 2010 Tomáš Müller<br>
014 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
015 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
016 * <br>
017 *          This library is free software; you can redistribute it and/or modify
018 *          it under the terms of the GNU Lesser General Public License as
019 *          published by the Free Software Foundation; either version 3 of the
020 *          License, or (at your option) any later version. <br>
021 * <br>
022 *          This library is distributed in the hope that it will be useful, but
023 *          WITHOUT ANY WARRANTY; without even the implied warranty of
024 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
025 *          Lesser General Public License for more details. <br>
026 * <br>
027 *          You should have received a copy of the GNU Lesser General Public
028 *          License along with this library; if not see
029 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
030 */
031
032public abstract class BinaryConstraint<V extends Variable<V, T>, T extends Value<V, T>> extends Constraint<V, T> {
033    private V iFirst = null, iSecond = null;
034
035    public BinaryConstraint() {
036        super();
037    }
038
039    @Override
040    public void addVariable(V var) {
041        if (iFirst == null)
042            iFirst = var;
043        else
044            iSecond = var;
045        super.addVariable(var);
046    }
047
048    /** First variable */
049    public V first() {
050        return iFirst;
051    }
052
053    /** Second variable */
054    public V second() {
055        return iSecond;
056    }
057
058    /** True, id the given variable is the first one */
059    public boolean isFirst(V variable) {
060        return variable.equals(first());
061    }
062
063    /**
064     * Returns the variable out of the constraints variables which is different
065     * from the given variable.
066     */
067    public V another(V variable) {
068        return (first() != null && variable.equals(first()) ? second() : first());
069    }
070}