001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  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    package org.apache.commons.math3.genetics;
018    
019    import java.util.ArrayList;
020    import java.util.List;
021    
022    import org.apache.commons.math3.exception.MathIllegalArgumentException;
023    import org.apache.commons.math3.exception.util.LocalizedFormats;
024    
025    /**
026     * Mutation for {@link BinaryChromosome}s. Randomly changes one gene.
027     *
028     * @version $Id: BinaryMutation.java 1416643 2012-12-03 19:37:14Z tn $
029     * @since 2.0
030     */
031    public class BinaryMutation implements MutationPolicy {
032    
033        /**
034         * Mutate the given chromosome. Randomly changes one gene.
035         *
036         * @param original the original chromosome.
037         * @return the mutated chromosome.
038         * @throws MathIllegalArgumentException if <code>original</code> is not an instance of {@link BinaryChromosome}.
039         */
040        public Chromosome mutate(Chromosome original) throws MathIllegalArgumentException {
041            if (!(original instanceof BinaryChromosome)) {
042                throw new MathIllegalArgumentException(LocalizedFormats.INVALID_BINARY_CHROMOSOME);
043            }
044    
045            BinaryChromosome origChrom = (BinaryChromosome) original;
046            List<Integer> newRepr = new ArrayList<Integer>(origChrom.getRepresentation());
047    
048            // randomly select a gene
049            int geneIndex = GeneticAlgorithm.getRandomGenerator().nextInt(origChrom.getLength());
050            // and change it
051            newRepr.set(geneIndex, origChrom.getRepresentation().get(geneIndex) == 0 ? 1 : 0);
052    
053            Chromosome newChrom = origChrom.newFixedLengthChromosome(newRepr);
054            return newChrom;
055        }
056    
057    }