001    package 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 Tomas Muller<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    
032    public 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    }