001 /*
002 * Java Genetic Algorithm Library (jenetics-1.6.0).
003 * Copyright (c) 2007-2014 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
024 import java.util.Random;
025
026 import org.jenetics.internal.util.HashBuilder;
027
028 import org.jenetics.util.IndexStream;
029 import org.jenetics.util.MSeq;
030 import org.jenetics.util.RandomRegistry;
031
032 /**
033 * The {@code SwapMutation} changes the order of genes in a chromosome, with the
034 * hope of bringing related genes closer together, thereby facilitating the
035 * production of building blocks. This mutation operator can also be used for
036 * combinatorial problems, where no duplicated genes within a chromosome are
037 * allowed, e.g. for the TSP.
038 *
039 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
040 * @since 1.0
041 * @version 1.0 — <em>$Date: 2014-02-27 $</em>
042 */
043 public class SwapMutator<G extends Gene<?, G>> extends Mutator<G> {
044
045 /**
046 * Constructs an alterer with a given recombination probability.
047 *
048 * @param probability the crossover probability.
049 * @throws IllegalArgumentException if the {@code probability} is not in the
050 * valid range of {@code [0, 1]}.
051 */
052 public SwapMutator(final double probability) {
053 super(probability);
054 }
055
056 /**
057 * Default constructor, with default mutation probability
058 * ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
059 */
060 public SwapMutator() {
061 this(DEFAULT_ALTER_PROBABILITY);
062 }
063
064 /**
065 * Swaps the genes in the given array, with the mutation probability of this
066 * mutation.
067 */
068 @Override
069 protected int mutate(final MSeq<G> genes, final double p) {
070 int alterations = 0;
071
072 if (genes.length() > 1) {
073 final Random random = RandomRegistry.getRandom();
074 final IndexStream stream = IndexStream.Random(
075 genes.length(), p, random
076 );
077
078 for (int i = stream.next(); i != -1; i = stream.next()) {
079 final int j = random.nextInt(genes.length());
080 genes.swap(i, j);
081
082 ++alterations;
083 }
084 }
085
086 return alterations;
087 }
088
089 @Override
090 public int hashCode() {
091 return HashBuilder.of(getClass()).and(super.hashCode()).value();
092 }
093
094 @Override
095 public boolean equals(final Object obj) {
096 if (obj == this) {
097 return true;
098 }
099 if (obj == null || obj.getClass() != getClass()) {
100 return false;
101 }
102
103 return super.equals(obj);
104 }
105
106 @Override
107 public String toString() {
108 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
109 }
110
111 }
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