SwapMutator.java
/*
* Java Genetic Algorithm Library (@__identifier__@).
* Copyright (c) @__year__@ Franz Wilhelmstötter
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Author:
* Franz Wilhelmstötter (franz.wilhelmstoetter@gmx.at)
*/
package org.jenetics;
import static java.lang.String.format;
import java.util.Random;
import org.jenetics.internal.util.HashBuilder;
import org.jenetics.util.IndexStream;
import org.jenetics.util.MSeq;
import org.jenetics.util.RandomRegistry;
/**
* The {@code SwapMutation} changes the order of genes in a chromosome, with the
* hope of bringing related genes closer together, thereby facilitating the
* production of building blocks. This mutation operator can also be used for
* combinatorial problems, where no duplicated genes within a chromosome are
* allowed, e.g. for the TSP.
*
* @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
* @since 1.0
* @version 1.0 — <em>$Date: 2014-02-27 $</em>
*/
public class SwapMutator<G extends Gene<?, G>> extends Mutator<G> {
/**
* Constructs an alterer with a given recombination probability.
*
* @param probability the crossover probability.
* @throws IllegalArgumentException if the {@code probability} is not in the
* valid range of {@code [0, 1]}.
*/
public SwapMutator(final double probability) {
super(probability);
}
/**
* Default constructor, with default mutation probability
* ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
*/
public SwapMutator() {
this(DEFAULT_ALTER_PROBABILITY);
}
/**
* Swaps the genes in the given array, with the mutation probability of this
* mutation.
*/
@Override
protected int mutate(final MSeq<G> genes, final double p) {
int alterations = 0;
if (genes.length() > 1) {
final Random random = RandomRegistry.getRandom();
final IndexStream stream = IndexStream.Random(
genes.length(), p, random
);
for (int i = stream.next(); i != -1; i = stream.next()) {
final int j = random.nextInt(genes.length());
genes.swap(i, j);
++alterations;
}
}
return alterations;
}
@Override
public int hashCode() {
return HashBuilder.of(getClass()).and(super.hashCode()).value();
}
@Override
public boolean equals(final Object obj) {
if (obj == this) {
return true;
}
if (obj == null || obj.getClass() != getClass()) {
return false;
}
return super.equals(obj);
}
@Override
public String toString() {
return format("%s[p=%f]", getClass().getSimpleName(), _probability);
}
}