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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.math.genetics;
18  
19  import java.util.ArrayList;
20  import java.util.List;
21  
22  /**
23   * Mutation for {@link BinaryChromosome}s. Randomly changes one gene.
24   *
25   * @version $Revision: 799857 $ $Date: 2009-08-01 09:07:12 -0400 (Sat, 01 Aug 2009) $
26   * @since 2.0
27   */
28  public class BinaryMutation implements MutationPolicy {
29  
30      /**
31       * Mutate the given chromosome. Randomly changes one gene.
32       * @param original the original chromosome.
33       * @return the mutated chromomsome.
34       */
35      public Chromosome mutate(Chromosome original) {
36          if (!(original instanceof BinaryChromosome)) {
37              throw new IllegalArgumentException("Binary mutation works on BinaryChromosome only."); 
38          }
39          
40          BinaryChromosome origChrom = (BinaryChromosome) original;
41          List<Integer> newRepr = new ArrayList<Integer>(origChrom.getRepresentation());
42          
43          // randomly select a gene
44          int geneIndex = GeneticAlgorithm.getRandomGenerator().nextInt(origChrom.getLength());
45          // and change it
46          newRepr.set(geneIndex, origChrom.getRepresentation().get(geneIndex) == 0 ? 1 : 0);
47          
48          Chromosome newChrom = origChrom.newFixedLengthChromosome(newRepr);
49          return newChrom;
50      }
51  
52  }