    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}