001 /*
002 * Java Genetic Algorithm Library (jenetics-1.5.0).
003 * Copyright (c) 2007-2013 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 * Author:
018 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmx.at)
019 */
020 package org.jenetics;
021
022 import static java.lang.String.format;
023 import static org.jenetics.util.object.hashCodeOf;
024
025 import java.util.Random;
026
027 import org.jenetics.util.IndexStream;
028 import org.jenetics.util.MSeq;
029 import org.jenetics.util.RandomRegistry;
030
031 /**
032 * The {@code SwapMutation} changes the order of genes in a chromosome, with the
033 * hope of bringing related genes closer together, thereby facilitating the
034 * production of building blocks. This mutation operator can also be used for
035 * combinatorial problems, where no duplicated genes within a chromosome are
036 * allowed, e.g. for the TSP.
037 *
038 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
039 * @since 1.0
040 * @version 1.0 — <em>$Date: 2013-08-30 $</em>
041 */
042 public class SwapMutator<G extends Gene<?, G>> extends Mutator<G> {
043
044 /**
045 * Constructs an alterer with a given recombination probability.
046 *
047 * @param probability the crossover probability.
048 * @throws IllegalArgumentException if the {@code probability} is not in the
049 * valid range of {@code [0, 1]}.
050 */
051 public SwapMutator(final double probability) {
052 super(probability);
053 }
054
055 /**
056 * Default constructor, with default mutation probability
057 * ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
058 */
059 public SwapMutator() {
060 this(DEFAULT_ALTER_PROBABILITY);
061 }
062
063 /**
064 * Swaps the genes in the given array, with the mutation probability of this
065 * mutation.
066 */
067 @Override
068 protected int mutate(final MSeq<G> genes, final double p) {
069 int alterations = 0;
070
071 if (genes.length() > 1) {
072 final Random random = RandomRegistry.getRandom();
073 final IndexStream stream = IndexStream.Random(
074 genes.length(), p, random
075 );
076
077 for (int i = stream.next(); i != -1; i = stream.next()) {
078 final int j = random.nextInt(genes.length());
079 genes.swap(i, j);
080
081 ++alterations;
082 }
083 }
084
085 return alterations;
086 }
087
088 @Override
089 public int hashCode() {
090 return hashCodeOf(getClass()).and(super.hashCode()).value();
091 }
092
093 @Override
094 public boolean equals(final Object obj) {
095 if (obj == this) {
096 return true;
097 }
098 if (obj == null || obj.getClass() != getClass()) {
099 return false;
100 }
101
102 return super.equals(obj);
103 }
104
105 @Override
106 public String toString() {
107 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
108 }
109
110 }
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