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With inspiration from other libraries

There is a newer version: 2.12.15

/*
 * 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.MathIllegalArgumentException;
import org.apache.commons.math3.exception.util.LocalizedFormats;

/**
 * Mutation operator for {@link RandomKey}s. Changes a randomly chosen element
 * of the array representation to a random value uniformly distributed in [0,1].
 *
 * @since 2.0
 */
public class RandomKeyMutation implements MutationPolicy {

    /**
     * {@inheritDoc}
     *
     * @throws MathIllegalArgumentException if original is not a {@link RandomKey} instance
     */
    public Chromosome mutate(final Chromosome original) throws MathIllegalArgumentException {
        if (!(original instanceof RandomKey)) {
            throw new MathIllegalArgumentException(LocalizedFormats.RANDOMKEY_MUTATION_WRONG_CLASS,
                                                   original.getClass().getSimpleName());
        }

        RandomKey originalRk = (RandomKey) original;
        List repr = originalRk.getRepresentation();
        int rInd = GeneticAlgorithm.getRandomGenerator().nextInt(repr.size());

        List newRepr = new ArrayList (repr);
        newRepr.set(rInd, GeneticAlgorithm.getRandomGenerator().nextDouble());

        return originalRk.newFixedLengthChromosome(newRepr);
    }

}