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Java example source code file (Chromosome.java)

This example Java source code file (Chromosome.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

chromosome, comparable, no_fitness, population

The Chromosome.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;

/**
 * Individual in a population. Chromosomes are compared based on their fitness.
 * <p>
 * The chromosomes are IMMUTABLE, and so their fitness is also immutable and
 * therefore it can be cached.
 *
 * @since 2.0
 */
public abstract class Chromosome implements Comparable<Chromosome>,Fitness {
    /** Value assigned when no fitness has been computed yet. */
    private static final double NO_FITNESS = Double.NEGATIVE_INFINITY;

    /** Cached value of the fitness of this chromosome. */
    private double fitness = NO_FITNESS;

    /**
     * Access the fitness of this chromosome. The bigger the fitness, the better the chromosome.
     * <p>
     * Computation of fitness is usually very time-consuming task, therefore the fitness is cached.
     *
     * @return the fitness
     */
    public double getFitness() {
        if (this.fitness == NO_FITNESS) {
            // no cache - compute the fitness
            this.fitness = fitness();
        }
        return this.fitness;
    }

    /**
     * Compares two chromosomes based on their fitness. The bigger the fitness, the better the chromosome.
     *
     * @param another another chromosome to compare
     * @return
     * <ul>
     *   <li>-1 if another is better than this
     *   <li>1 if another is worse than this
     *   <li>0 if the two chromosomes have the same fitness
     * </ul>
     */
    public int compareTo(final Chromosome another) {
        return Double.compare(getFitness(), another.getFitness());
    }

    /**
     * Returns <code>true iff another has the same representation and therefore the same fitness. By
     * default, it returns false -- override it in your implementation if you need it.
     *
     * @param another chromosome to compare
     * @return true if <code>another is equivalent to this chromosome
     */
    protected boolean isSame(final Chromosome another) {
        return false;
    }

    /**
     * Searches the <code>population for another chromosome with the same representation. If such chromosome is
     * found, it is returned, if no such chromosome exists, returns <code>null.
     *
     * @param population Population to search
     * @return Chromosome with the same representation, or <code>null if no such chromosome exists.
     */
    protected Chromosome findSameChromosome(final Population population) {
        for (Chromosome anotherChr : population) {
            if (this.isSame(anotherChr)) {
                return anotherChr;
            }
        }
        return null;
    }

    /**
     * Searches the population for a chromosome representing the same solution, and if it finds one,
     * updates the fitness to its value.
     *
     * @param population Population to search
     */
    public void searchForFitnessUpdate(final Population population) {
        Chromosome sameChromosome = findSameChromosome(population);
        if (sameChromosome != null) {
            fitness = sameChromosome.getFitness();
        }
    }

}

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