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 }