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Java example source code file (OnePointCrossover.java)

This example Java source code file (OnePointCrossover.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

abstractlistchromosome, arraylist, chromosomepair, crossoverpolicy, dimensionmismatchexception, list, mathillegalargumentexception, onepointcrossover, suppresswarnings, util

The OnePointCrossover.java Java example source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.apache.commons.math3.genetics;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.util.LocalizedFormats;


/**
 * One point crossover policy. A random crossover point is selected and the
 * first part from each parent is copied to the corresponding child, and the
 * second parts are copied crosswise.
 *
 * Example:
 * <pre>
 * -C- denotes a crossover point
 *                   -C-                                 -C-
 * p1 = (1 0 1 0 0 1  | 0 1 1)    X    p2 = (0 1 1 0 1 0  | 1 1 1)
 *      \------------/ \-----/              \------------/ \-----/
 *            ||         (*)                       ||        (**)
 *            VV         (**)                      VV        (*)
 *      /------------\ /-----\              /------------\ /-----\
 * c1 = (1 0 1 0 0 1  | 1 1 1)    X    c2 = (0 1 1 0 1 0  | 0 1 1)
 * </pre>
 *
 * This policy works only on {@link AbstractListChromosome}, and therefore it
 * is parameterized by T. Moreover, the chromosomes must have same lengths.
 *
 * @param <T> generic type of the {@link AbstractListChromosome}s for crossover
 * @since 2.0
 *
 */
public class OnePointCrossover<T> implements CrossoverPolicy {

    /**
     * Performs one point crossover. A random crossover point is selected and the
     * first part from each parent is copied to the corresponding child, and the
     * second parts are copied crosswise.
     *
     * Example:
     * <pre>
     * -C- denotes a crossover point
     *                   -C-                                 -C-
     * p1 = (1 0 1 0 0 1  | 0 1 1)    X    p2 = (0 1 1 0 1 0  | 1 1 1)
     *      \------------/ \-----/              \------------/ \-----/
     *            ||         (*)                       ||        (**)
     *            VV         (**)                      VV        (*)
     *      /------------\ /-----\              /------------\ /-----\
     * c1 = (1 0 1 0 0 1  | 1 1 1)    X    c2 = (0 1 1 0 1 0  | 0 1 1)
     * </pre>
     *
     * @param first first parent (p1)
     * @param second second parent (p2)
     * @return pair of two children (c1,c2)
     * @throws MathIllegalArgumentException iff one of the chromosomes is
     *   not an instance of {@link AbstractListChromosome}
     * @throws DimensionMismatchException if the length of the two chromosomes is different
     */
    @SuppressWarnings("unchecked") // OK because of instanceof checks
    public ChromosomePair crossover(final Chromosome first, final Chromosome second)
        throws DimensionMismatchException, MathIllegalArgumentException {

        if (! (first instanceof AbstractListChromosome<?> && second instanceof AbstractListChromosome)) {
            throw new MathIllegalArgumentException(LocalizedFormats.INVALID_FIXED_LENGTH_CHROMOSOME);
        }
        return crossover((AbstractListChromosome<T>) first, (AbstractListChromosome) second);
    }


    /**
     * Helper for {@link #crossover(Chromosome, Chromosome)}. Performs the actual crossover.
     *
     * @param first the first chromosome.
     * @param second the second chromosome.
     * @return the pair of new chromosomes that resulted from the crossover.
     * @throws DimensionMismatchException if the length of the two chromosomes is different
     */
    private ChromosomePair crossover(final AbstractListChromosome<T> first,
                                     final AbstractListChromosome<T> second) throws DimensionMismatchException {
        final int length = first.getLength();
        if (length != second.getLength()) {
            throw new DimensionMismatchException(second.getLength(), length);
        }

        // array representations of the parents
        final List<T> parent1Rep = first.getRepresentation();
        final List<T> parent2Rep = second.getRepresentation();
        // and of the children
        final List<T> child1Rep = new ArrayList(length);
        final List<T> child2Rep = new ArrayList(length);

        // select a crossover point at random (0 and length makes no sense)
        final int crossoverIndex = 1 + (GeneticAlgorithm.getRandomGenerator().nextInt(length-2));

        // copy the first part
        for (int i = 0; i < crossoverIndex; i++) {
            child1Rep.add(parent1Rep.get(i));
            child2Rep.add(parent2Rep.get(i));
        }
        // and switch the second part
        for (int i = crossoverIndex; i < length; i++) {
            child1Rep.add(parent2Rep.get(i));
            child2Rep.add(parent1Rep.get(i));
        }

        return new ChromosomePair(first.newFixedLengthChromosome(child1Rep),
                                  second.newFixedLengthChromosome(child2Rep));
    }

}

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