PopulationIterator.java

package net.bmahe.genetics4j.core;

import java.util.Iterator;

import org.apache.commons.lang3.Validate;

/**

 * Iterator implementation for traversing individuals in a population during evolutionary algorithms.

 * 

 * <p>PopulationIterator provides a standard Java Iterator interface for accessing individuals

 * in a {@link Population}, combining genotypes with their corresponding fitness values to create

 * complete {@link Individual} instances during iteration.

 * 

 * <p>This iterator enables convenient traversal patterns such as:

 * <ul>

 * <li><strong>Enhanced for loops</strong>: Iterate over individuals using for-each syntax</li>

 * <li><strong>Stream operations</strong>: Convert populations to streams for functional processing</li>

 * <li><strong>Sequential access</strong>: Process individuals one at a time without loading all into memory</li>

 * <li><strong>Collection integration</strong>: Use with Java Collection framework methods</li>

 * </ul>

 * 

 * <p>The iterator maintains internal state to track the current position and constructs

 * {@link Individual} objects on-demand by combining genotypes and fitness values from the

 * underlying population at the same index.

 * 

 * <p>Key characteristics:

 * <ul>

 * <li><strong>Type safety</strong>: Parameterized with fitness type for compile-time type checking</li>

 * <li><strong>Lazy evaluation</strong>: Creates Individual objects only when requested</li>

 * <li><strong>Memory efficient</strong>: Doesn't duplicate population data, references original</li>

 * <li><strong>Standard interface</strong>: Implements Java Iterator contract completely</li>

 * </ul>

 * 

 * <p>Usage patterns:

 * <pre>{@code

 * // Enhanced for loop iteration

 * Population<Double> population = getPopulation();

 * for (Individual<Double> individual : population) {

 *     System.out.println("Fitness: " + individual.fitness());

 * }

 * 

 * // Stream-based processing

 * population.stream()

 *     .filter(individual -> individual.fitness() > threshold)

 *     .mapToDouble(Individual::fitness)

 *     .average();

 * 

 * // Manual iteration

 * Iterator<Individual<Double>> iterator = population.iterator();

 * while (iterator.hasNext()) {

 *     Individual<Double> individual = iterator.next();

 *     processIndividual(individual);

 * }

 * }</pre>

 * 

 * <p>Thread safety considerations:

 * <ul>

 * <li><strong>Single-threaded use</strong>: Iterator instances are not thread-safe</li>

 * <li><strong>Population stability</strong>: Underlying population should not be modified during iteration</li>

 * <li><strong>Concurrent iterations</strong>: Multiple iterators can be created for the same population</li>

 * </ul>

 * 

 * @param <T> the type of fitness values in the population, must be comparable for selection operations

 * @see Population

 * @see Individual

 * @see java.util.Iterator

 */

public class PopulationIterator<T extends Comparable<T>> implements Iterator<Individual<T>> {

	private final Population<T> population;

	/**

	 * Constructs a new iterator for the specified population.

	 * 

	 * <p>Creates an iterator that will traverse all individuals in the given population,

	 * starting from index 0 and proceeding sequentially through all individuals.

	 * 

	 * @param _population the population to iterate over

	 * @throws IllegalArgumentException if the population is null

	 */

	/**

	 * Returns {@code true} if there are more individuals to iterate over.

	 * 

	 * <p>Checks whether the current position is within the bounds of the population.

	 * This method can be called multiple times without advancing the iterator position.

	 * 

	 * @return {@code true} if there are more individuals, {@code false} if all have been visited

	 */

	@Override

	public boolean hasNext() {

	}

	/**

	 * Returns the next individual in the population and advances the iterator position.

	 * 

	 * <p>Constructs an {@link Individual} by combining the genotype and fitness value

	 * at the current position, then advances to the next position for subsequent calls.

	 * 

	 * @return the next individual in the iteration sequence

	 * @throws java.util.NoSuchElementException if there are no more individuals (when {@link #hasNext()} returns false)

	 */

	@Override

	public Individual<T> next() {

	}

}

Mutations

1.1
Location : <init>
Killed by : none Removed assignment to member variable currentIndex → SURVIVED Covering tests

2.2
Location : <init>
Killed by : net.bmahe.genetics4j.core.PopulationIteratorTest.[engine:junit-jupiter]/[class:net.bmahe.genetics4j.core.PopulationIteratorTest]/[method:nextReturnsCorrectIndividual()] Substituted 0 with 1 → KILLED