TruncationSelector.java
/*
* Java Genetic Algorithm Library (@__identifier__@).
* Copyright (c) @__year__@ Franz Wilhelmstötter
*
* Licensed 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.
*
* Author:
* Franz Wilhelmstötter (franz.wilhelmstoetter@gmx.at)
*/
package org.jenetics;
import static java.lang.String.format;
import static java.util.Objects.requireNonNull;
import org.jenetics.internal.util.HashBuilder;
/**
* In truncation selection individuals are sorted according to their fitness.
* Only the n best individuals are selected. The truncation selection is a very
* basic selection algorithm. It has it's strength in fast selecting individuals
* in large populations, but is not very often used in practice.
*
* @see <a href="http://en.wikipedia.org/wiki/Truncation_selection">
* Wikipedia: Truncation selection
* </a>
*
* @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
* @since 1.0
* @version 1.0 — <em>$Date: 2014-02-27 $</em>
*/
public final class TruncationSelector<
G extends Gene<?, G>,
C extends Comparable<? super C>
>
implements Selector<G, C>
{
/**
* Create a new TruncationSelector object.
*/
public TruncationSelector() {
}
/**
* This method sorts the population in descending order while calculating the
* selection probabilities. (The method {@link Population#sort()} is called
* by this method.)
*
* @throws IllegalArgumentException if the sample size is greater than the
* population size or {@code count} is greater the the population
* size.
* @throws NullPointerException if the {@code population} is {@code null}.
*/
@Override
public Population<G, C> select(
final Population<G, C> population,
final int count,
final Optimize opt
) {
requireNonNull(population, "Population");
requireNonNull(opt, "Optimization");
if (count < 0) {
throw new IllegalArgumentException(format(
"Selection count must be greater or equal then zero, but was %s",
count
));
}
if (count > population.size()) {
throw new IllegalArgumentException(format(
"Selection size greater than population size: %s > %s",
count, population.size()
));
}
population.sortWith(opt.<C>descending());
return new Population<>(population.subList(0, count));
}
@Override
public int hashCode() {
return HashBuilder.of(getClass()).value();
}
@Override
public boolean equals(final Object obj) {
return obj == this || obj instanceof TruncationSelector<?, ?>;
}
@Override
public String toString() {
return getClass().getName();
}
}