@SuppressWarnings("unchecked")
protected KeyedChromosome<Object> performCrossover(
KeyedChromosome<Object> parentA, KeyedChromosome<Object> parentB) {
KeyedChromosome<Object> child = (KeyedChromosome<Object>) parentA.clone();
Map<Object, Gene> replaced = new HashMap<Object, Gene>();
double originalFitness = parentA.getFitness();
Gene originalGene;
Gene replacement;
boolean crossedOver;
int attempts = 0;
for (; attempts < maxAttempts; attempts++) {
crossedOver = false;
replaced.clear();
for (Object key : child.getGenes().keySet()) {
if (coin.flip()) {
originalGene = child.getGenes().get(key);
replacement = parentB.getGenes().get(key).clone();
if (!replacement.equals(originalGene)) {
replaced.put(key, originalGene);
child.replaceGene(key, replacement);
crossedOver = true;
}
}
}
if (crossedOver) {
double fitness = fitnessEvaluator.evaluate(child);
if (fitness > originalFitness) {
child.setFitness(fitness);
break;
} else {
// revert crossover
for (Object key : replaced.keySet()) {
child.replaceGene(key, replaced.get(key));
}
// Make sure it doesn't get re-evaluated
child.setFitness(originalFitness);
}
}
}
if (attempts >= maxAttempts) {
log.debug(
"Unable to find guaranteed better fitness via crossover after "
+ maxAttempts
+ " attempts. Returning clone of first parent.");
}
return child;
}
@Override
public List<KeyedChromosome<Object>> crossover(
KeyedChromosome<Object> parentA, KeyedChromosome<Object> parentB) {
List<KeyedChromosome<Object>> children = new ArrayList<KeyedChromosome<Object>>(1);
KeyedChromosome<Object> child = performCrossover(parentA, parentB);
// The Chromosome could be null if it's identical to one of its parents
if (child != null) {
children.add(child);
if (maxGenerations > 0) {
child.setAncestry(
new Ancestry(
parentA.getId(),
parentB.getId(),
parentA.getAncestry(),
parentB.getAncestry(),
maxGenerations));
}
parentA.increaseNumberOfChildren();
parentB.increaseNumberOfChildren();
}
return children;
}