Package net.bmahe.genetics4j.core

Interface Fitness<T extends Comparable<T>>

Type Parameters:
T - the type of the fitness value, must be comparable for selection operations
Functional Interface:
This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
@FunctionalInterface public interface Fitness<T extends Comparable<T>>
Functional interface for evaluating the fitness of a genotype in an evolutionary algorithm.

The fitness function is a crucial component of evolutionary algorithms as it determines the quality or performance of individual solutions. It maps a genotype to a fitness value that can be used for selection, ranking, and determining evolutionary progress.

Implementations should be:

  • Deterministic: The same genotype should always produce the same fitness value
  • Thread-safe: May be called concurrently from multiple threads
  • Fast: Called frequently during evolution, performance matters

Common fitness function patterns:

  • Minimization: Lower values indicate better solutions (errors, costs)
  • Maximization: Higher values indicate better solutions (profits, accuracy)
  • Multi-objective: Use FitnessVector from the MOO module for multiple objectives
See Also:

  • Method Summary

    Modifier and Type
    Method
    Description
    T
    compute(Genotype genotype)
    Computes the fitness value for the specified genotype.
    static <U, V extends Comparable<V>>
    Fitness<V>
    forChromosome(int chromosomeIndex, Function<U,V> chromosomeFitness)
    Creates a fitness function that evaluates a specific chromosome within a genotype.

  • Method Details

    • compute

      T compute(Genotype genotype)
      Computes the fitness value for the specified genotype.

      This method should evaluate how well the genotype solves the problem and return a comparable fitness value. The interpretation of "better" depends on whether the optimization is for minimization or maximization.

      Parameters:
      genotype - the genotype to evaluate
      Returns:
      the fitness value representing the quality of the genotype
      Throws:
      RuntimeException - if evaluation fails due to invalid genotype or computation error

    • forChromosome

      static <U, V extends Comparable<V>> Fitness<V> forChromosome(int chromosomeIndex, Function<U,V> chromosomeFitness)
      Creates a fitness function that evaluates a specific chromosome within a genotype.

      This utility method simplifies fitness evaluation when the fitness depends on only one chromosome from the genotype. It extracts the chromosome at the specified index and applies the provided fitness function to it.

      This is particularly useful for:

      • Single-chromosome problems where genotype contains only one chromosome
      • Multi-chromosome problems where fitness depends on one specific chromosome
      • Compositional fitness functions that evaluate chromosomes independently
      Type Parameters:
      U - the type of the chromosome to evaluate
      V - the type of the fitness value, must be comparable
      Parameters:
      chromosomeIndex - the zero-based index of the chromosome to evaluate within the genotype
      chromosomeFitness - the function that computes fitness for the extracted chromosome
      Returns:
      a fitness function that evaluates the specified chromosome
      Throws:
      IllegalArgumentException - if chromosomeIndex is negative
      NullPointerException - if chromosomeFitness is null
      ClassCastException - at runtime if the chromosome at the specified index cannot be cast to type U
      IllegalArgumentException - at runtime if chromosomeIndex exceeds the genotype size