001 /*
002 * Java Genetic Algorithm Library (jenetics-4.0.0).
003 * Copyright (c) 2007-2017 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 */
020 package io.jenetics.engine;
021
022 import java.util.function.Function;
023 import java.util.function.Predicate;
024 import java.util.function.Supplier;
025 import java.util.stream.Stream;
026
027 import io.jenetics.Gene;
028
029 /**
030 * The {@code EvolutionStream} class extends the Java {@link Stream} and adds a
031 * method for limiting the evolution by a given predicate.
032 *
033 * @see java.util.stream.Stream
034 * @see Engine
035 *
036 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
037 * @since 3.0
038 * @version 3.1
039 */
040 public interface EvolutionStream<
041 G extends Gene<?, G>,
042 C extends Comparable<? super C>
043 >
044 extends Stream<EvolutionResult<G, C>>
045 {
046
047 /**
048 * Returns a stream consisting of the elements of this stream, truncated
049 * when the given {@code proceed} predicate returns {@code false}.
050 * <p>
051 * <i>General usage example:</i>
052 * <pre>{@code
053 * final Phenotype<DoubleGene, Double> result = engine.stream()
054 * // Truncate the evolution stream after 5 "steady" generations.
055 * .limit(bySteadyFitness(5))
056 * // The evolution will stop after maximal 100 generations.
057 * .limit(100)
058 * .collect(toBestPhenotype());
059 * }</pre>
060 *
061 * @see Limits
062 *
063 * @param proceed the predicate which determines whether the stream is
064 * truncated or not. <i>If the predicate returns {@code false}, the
065 * evolution stream is truncated.</i>
066 * @return the new stream
067 * @throws NullPointerException if the given predicate is {@code null}.
068 */
069 public EvolutionStream<G, C>
070 limit(final Predicate<? super EvolutionResult<G, C>> proceed);
071
072 /**
073 * Create a new {@code EvolutionStream} from the given {@code start}
074 * population and {@code evolution} function. The main purpose of this
075 * factory method is to simplify the creation of an {@code EvolutionStream}
076 * from an own evolution (GA) engine.
077 *
078 * <pre>{@code
079 * final Supplier<EvolutionStart<DoubleGene, Double>> start = ...
080 * final EvolutionStream<DoubleGene, Double> stream =
081 * EvolutionStream.of(start, new MySpecialEngine());
082 * }</pre>
083 *
084 * A more complete example for would look like as:
085 *
086 * <pre>{@code
087 * public final class SpecialEngine {
088 *
089 * // The fitness function.
090 * private static Double fitness(final Genotype<DoubleGene> gt) {
091 * return gt.getGene().getAllele();
092 * }
093 *
094 * // Create new evolution start object.
095 * private static EvolutionStart<DoubleGene, Double>
096 * start(final int populationSize, final long generation) {
097 * final Population<DoubleGene, Double> population =
098 * Genotype.of(DoubleChromosome.of(0, 1)).instances()
099 * .map(gt -> Phenotype.of(gt, generation, SpecialEngine::fitness))
100 * .limit(populationSize)
101 * .collect(Population.toPopulation());
102 *
103 * return EvolutionStart.of(population, generation);
104 * }
105 *
106 * // The special evolution function.
107 * private static EvolutionResult<DoubleGene, Double>
108 * evolve(final EvolutionStart<DoubleGene, Double> start) {
109 * // Your special evolution implementation comes here!
110 * return null;
111 * }
112 *
113 * public static void main(final String[] args) {
114 * final Genotype<DoubleGene> best = EvolutionStream
115 * .of(() -> start(50, 0), SpecialEngine::evolve)
116 * .limit(Limits.bySteadyFitness(10))
117 * .limit(1000)
118 * .collect(EvolutionResult.toBestGenotype());
119 *
120 * System.out.println(String.format("Best Genotype: %s", best));
121 * }
122 * }
123 * }</pre>
124 *
125 *
126 * @since 3.1
127 *
128 * @param <G> the gene type
129 * @param <C> the fitness type
130 * @param start the evolution start
131 * @param evolution the evolution function
132 * @return a new {@code EvolutionStream} with the given {@code start} and
133 * {@code evolution} function
134 * @throws java.lang.NullPointerException if one of the arguments is
135 * {@code null}
136 */
137 public static <G extends Gene<?, G>, C extends Comparable<? super C>>
138 EvolutionStream<G, C> of(
139 final Supplier<EvolutionStart<G, C>> start,
140 final Function<? super EvolutionStart<G, C>, EvolutionResult<G, C>> evolution
141 ) {
142 return new EvolutionStreamImpl<>(start, evolution);
143 }
144
145 }
|