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 * @author  Tomáš Müller
013 * @version IFS 1.3 (Iterative Forward Search)<br>
014 *          Copyright (C) 2006 - 2014 Tomáš Müller<br>
015 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
016 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
017 * <br>
018 *          This library is free software; you can redistribute it and/or modify
019 *          it under the terms of the GNU Lesser General Public License as
020 *          published by the Free Software Foundation; either version 3 of the
021 *          License, or (at your option) any later version. <br>
022 * <br>
023 *          This library is distributed in the hope that it will be useful, but
024 *          WITHOUT ANY WARRANTY; without even the implied warranty of
025 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
026 *          Lesser General Public License for more details. <br>
027 * <br>
028 *          You should have received a copy of the GNU Lesser General Public
029 *          License along with this library; if not see
030 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
031 * @param <V> Variable
032 * @param <T> Value
033 */
034
035public abstract class BinaryConstraint<V extends Variable<V, T>, T extends Value<V, T>> extends Constraint<V, T> {
036    private V iFirst = null, iSecond = null;
037
038    public BinaryConstraint() {
039        super();
040    }
041
042    @Override
043    public void addVariable(V var) {
044        if (iFirst == null)
045            iFirst = var;
046        else
047            iSecond = var;
048        super.addVariable(var);
049    }
050
051    /** First variable 
052     * @return first variable of the constraint 
053     **/
054    public V first() {
055        return iFirst;
056    }
057
058    /** Second variable 
059     * @return second variable of the constraint 
060     **/
061    public V second() {
062        return iSecond;
063    }
064
065    /** True, id the given variable is the first one 
066     * @param variable given variable
067     * @return true if the given variable is the first variable of the constraint
068     **/
069    public boolean isFirst(V variable) {
070        return variable.equals(first());
071    }
072
073    /**
074     * Returns the variable out of the constraints variables which is different
075     * from the given variable.
076     * @param variable given variable
077     * @return the other variable of the constraint
078     */
079    public V another(V variable) {
080        return (first() != null && variable.equals(first()) ? second() : first());
081    }
082}