001 /*
002 * Java Genetic Algorithm Library (jenetics-3.7.0).
003 * Copyright (c) 2007-2016 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@gmx.at)
019 */
020 package org.jenetics;
021
022 import org.jenetics.util.ISeq;
023
024 /**
025 * The Alterer is responsible for the changing/recombining the Population.
026 * Alterers can be chained by appending a list of alterers with the
027 * {@link org.jenetics.engine.Engine.Builder#alterers(Alterer, Alterer[])} method.
028 *
029 * <pre>{@code
030 * final Engine<DoubleGene, Double> engine = Engine
031 * .builder(gtf, ff)
032 * .alterers(
033 * new Crossover<>(0.1),
034 * new Mutator<>(0.05),
035 * new MeanAlterer<>(0.2))
036 * .build();
037 * final EvolutionStream<DoubleGene, Double> stream = engine.stream();
038 * }</pre>
039 *
040 * The order of the alterer calls is: Crossover, Mutation and MeanAlterer.
041 *
042 * @param <G> the gene type
043 * @param <C> the fitness function result type
044 *
045 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
046 * @since 1.0
047 * @version 3.0
048 */
049 @FunctionalInterface
050 public interface Alterer<
051 G extends Gene<?, G>,
052 C extends Comparable<? super C>
053 >
054 {
055
056 public static final double DEFAULT_ALTER_PROBABILITY = 0.2;
057
058 /**
059 * Alters (recombine) a given population. If the {@code population} is empty,
060 * nothing is altered. The altering of the population is done in place; the
061 * given <i>population</i> is altered.
062 *
063 * @param population The Population to be altered. If the
064 * {@code population} is {@code null} or empty, nothing is altered.
065 * @param generation the date of birth (generation) of the altered phenotypes.
066 * @return the number of genes that has been altered.
067 * @throws NullPointerException if the given {@code population} is
068 * {@code null}.
069 */
070 public int alter(final Population<G, C> population, final long generation);
071
072 /**
073 * Returns a composed alterer that first applies the {@code before} alterer
074 * to its input, and then applies {@code this} alterer to the result.
075 *
076 * @param before the alterer to apply first
077 * @return the new composed alterer
078 */
079 public default Alterer<G, C> compose(final Alterer<G, C> before) {
080 return of(before, this);
081 }
082
083 /**
084 * Returns a composed alterer that applies the {@code this} alterer
085 * to its input, and then applies the {@code after} alterer to the result.
086 *
087 * @param after the alterer to apply first
088 * @return the new composed alterer
089 */
090 public default Alterer<G, C> andThen(final Alterer<G, C> after) {
091 return of(this, after);
092 }
093
094 /**
095 * Combine the given alterers.
096 *
097 * @param <G> the gene type
098 * @param <C> the fitness function result type
099 * @param alterers the alterers to combine.
100 * @return a new alterer which consists of the given one
101 * @throws NullPointerException if one of the alterers is {@code null}.
102 */
103 @SafeVarargs
104 public static <G extends Gene<?, G>, C extends Comparable<? super C>>
105 Alterer<G, C> of(final Alterer<G, C>... alterers) {
106 return alterers.length == 0
107 ? (p, g) -> 0
108 : alterers.length == 1
109 ? alterers[0]
110 : new CompositeAlterer<>(ISeq.of(alterers));
111 }
112
113 }
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