001/*
002 * Java Genetic Algorithm Library (jenetics-8.3.0).
003 * Copyright (c) 2007-2025 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 * {@snippet lang="java":
032 * final Engine<DoubleGene, Double> engine = Engine
033 *     .builder(gtf, ff)
034 *     .alterers(
035 *         new Crossover<>(0.1),
036 *         new Mutator<>(0.05),
037 *         new MeanAlterer<>(0.2))
038 *     .build();
039 * final EvolutionStream<DoubleGene, Double> stream = engine.stream();
040 * }
041 *
042 * The order of the alterer calls is: Crossover, Mutation and MeanAlterer.
043 *
044 * @param <G> the gene type
045 * @param <C> the fitness function result type
046 *
047 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
048 * @since 1.0
049 * @version 4.0
050 */
051@FunctionalInterface
052public interface Alterer<
053        G extends Gene<?, G>,
054        C extends Comparable<? super C>
055> {
056
057        /**
058         * The default alter probability: 0.2
059         */
060        double DEFAULT_ALTER_PROBABILITY = 0.2;
061
062        /**
063         * Alters (recombine) a given population. If the {@code population} is empty,
064         * nothing is altered. The altered population is part of the returned
065         * {@code AlterResult} object.
066         *
067         * @param population The Population to be altered. If the {@code population}
068         *        is {@code null} or empty, nothing is altered.
069         * @param generation the date of birth (generation) of the altered phenotypes.
070         * @return the alter-result object, which contains the altered population
071         *         and the alteration counts
072         * @throws NullPointerException if the given {@code population} is
073         *        {@code null}.
074         */
075        AltererResult<G, C> alter(
076                final Seq<Phenotype<G, C>> population,
077                final long generation
078        );
079
080        /**
081         * Returns a composed alterer that first applies the {@code before} alterer
082         * to its input, and then applies {@code this} alterer to the result.
083         *
084         * @param before the alterer to apply first
085         * @return the new composed alterer
086         */
087        default Alterer<G, C> compose(final Alterer<G, C> before) {
088                return of(requireNonNull(before), this);
089        }
090
091        /**
092         * Returns a composed alterer that applies the {@code this} alterer
093         * to its input, and then applies the {@code after} alterer to the result.
094         *
095         * @param after the alterer to apply first
096         * @return the new composed alterer
097         */
098        default Alterer<G, C> andThen(final Alterer<G, C> after) {
099                return of(this, requireNonNull(after));
100        }
101
102        /**
103         * Combine the given alterers.
104         *
105         * @param <G> the gene type
106         * @param <C> the fitness function result type
107         * @param alterers the alterers to combine.
108         * @return a new alterer which consists of the given one
109         * @throws NullPointerException if one of the alterers is {@code null}.
110         */
111        @SafeVarargs
112        static <G extends Gene<?, G>, C extends Comparable<? super C>>
113        Alterer<G, C> of(final Alterer<G, C>... alterers) {
114                return alterers.length == 0
115                        ? (p, g) -> new AltererResult<>(p.asISeq())
116                        : alterers.length == 1
117                                ? alterers[0]
118                                : new CompositeAlterer<>(ISeq.of(alterers));
119        }
120
121}