001/*
002 * Java Genetic Algorithm Library (jenetics-8.1.0).
003 * Copyright (c) 2007-2024 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * 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 * Author:
018 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020package io.jenetics;
021
022import static java.util.Objects.requireNonNull;
023
024import io.jenetics.util.ISeq;
025import io.jenetics.util.Seq;
026
027/**
028 * The Alterer is responsible for the changing/recombining the Population.
029 * Alterers can be chained by appending a list of alterers with the
030 * {@link io.jenetics.engine.Engine.Builder#alterers(Alterer, Alterer[])} method.
031 *
032 * {@snippet lang="java":
033 * final Engine<DoubleGene, Double> engine = Engine
034 *     .builder(gtf, ff)
035 *     .alterers(
036 *         new Crossover<>(0.1),
037 *         new Mutator<>(0.05),
038 *         new MeanAlterer<>(0.2))
039 *     .build();
040 * final EvolutionStream<DoubleGene, Double> stream = engine.stream();
041 * }
042 *
043 * The order of the alterer calls is: Crossover, Mutation and MeanAlterer.
044 *
045 * @param <G> the gene type
046 * @param <C> the fitness function result type
047 *
048 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
049 * @since 1.0
050 * @version 4.0
051 */
052@FunctionalInterface
053public interface Alterer<
054        G extends Gene<?, G>,
055        C extends Comparable<? super C>
056> {
057
058        /**
059         * The default alter probability: 0.2
060         */
061        double DEFAULT_ALTER_PROBABILITY = 0.2;
062
063        /**
064         * Alters (recombine) a given population. If the {@code population} is empty,
065         * nothing is altered. The altered population is part of the returned
066         * {@code AlterResult} object.
067         *
068         * @param population The Population to be altered. If the {@code population}
069         *        is {@code null} or empty, nothing is altered.
070         * @param generation the date of birth (generation) of the altered phenotypes.
071         * @return the alter-result object, which contains the altered population
072         *         and the alteration counts
073         * @throws NullPointerException if the given {@code population} is
074         *        {@code null}.
075         */
076        AltererResult<G, C> alter(
077                final Seq<Phenotype<G, C>> population,
078                final long generation
079        );
080
081        /**
082         * Returns a composed alterer that first applies the {@code before} alterer
083         * to its input, and then applies {@code this} alterer to the result.
084         *
085         * @param before the alterer to apply first
086         * @return the new composed alterer
087         */
088        default Alterer<G, C> compose(final Alterer<G, C> before) {
089                return of(requireNonNull(before), this);
090        }
091
092        /**
093         * Returns a composed alterer that applies the {@code this} alterer
094         * to its input, and then applies the {@code after} alterer to the result.
095         *
096         * @param after the alterer to apply first
097         * @return the new composed alterer
098         */
099        default Alterer<G, C> andThen(final Alterer<G, C> after) {
100                return of(this, requireNonNull(after));
101        }
102
103        /**
104         * Combine the given alterers.
105         *
106         * @param <G> the gene type
107         * @param <C> the fitness function result type
108         * @param alterers the alterers to combine.
109         * @return a new alterer which consists of the given one
110         * @throws NullPointerException if one of the alterers is {@code null}.
111         */
112        @SafeVarargs
113        static <G extends Gene<?, G>, C extends Comparable<? super C>>
114        Alterer<G, C> of(final Alterer<G, C>... alterers) {
115                return alterers.length == 0
116                        ? (p, g) -> new AltererResult<>(p.asISeq())
117                        : alterers.length == 1
118                                ? alterers[0]
119                                : new CompositeAlterer<>(ISeq.of(alterers));
120        }
121
122}