    001package org.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 1.3 (Iterative Forward Search)<br>
    013 *          Copyright (C) 2006 - 2014 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 * @param <V> Variable
    031 * @param <T> Value
    032 */
    033
    034public abstract class BinaryConstraint<V extends Variable<V, T>, T extends Value<V, T>> extends Constraint<V, T> {
    035    private V iFirst = null, iSecond = null;
    036
    037    public BinaryConstraint() {
    038        super();
    039    }
    040
    041    @Override
    042    public void addVariable(V var) {
    043        if (iFirst == null)
    044            iFirst = var;
    045        else
    046            iSecond = var;
    047        super.addVariable(var);
    048    }
    049
    050    /** First variable
    051     * @return first variable of the constraint
    052     **/
    053    public V first() {
    054        return iFirst;
    055    }
    056
    057    /** Second variable
    058     * @return second variable of the constraint
    059     **/
    060    public V second() {
    061        return iSecond;
    062    }
    063
    064    /** True, id the given variable is the first one
    065     * @param variable given variable
    066     * @return true if the given variable is the first variable of the constraint
    067     **/
    068    public boolean isFirst(V variable) {
    069        return variable.equals(first());
    070    }
    071
    072    /**
    073     * Returns the variable out of the constraints variables which is different
    074     * from the given variable.
    075     * @param variable given variable
    076     * @return the other variable of the constraint
    077     */
    078    public V another(V variable) {
    079        return (first() != null && variable.equals(first()) ? second() : first());
    080    }
    081}