Foo.java

public class Foo {
  //...

  private List<Phrase> breed(List<Phrase> currentPopulation) {
    List<Phrase> newPopulation = currentPopulation.subList(31, 95);
    List<Phrase> breedingPool = new ArrayList<>(newPopulation);

    //pick two random species
    Random r = new Random();
    for(int i = 0; i < 32; i++) {
      int index1 = r.nextInt(breedingPool.size());
      Phrase phrase1 = breedingPool.remove(index1);
      int index2 = r.nextInt(breedingPool.size());
      Phrase phrase2 = breedingPool.remove(index2);

      newPopulation.add(sexytime(phrase1, phrase2));
    }

    return newPopulation;
  }
  
  public Phrase sexytime(Phrase first, Phrase second) {
      Random r = new Random();

      int crossoverPoint = r.nextInt(first.dna.size() - 1);

      //determine whether 1st half of first + 2nd half of second or vice versa
      List<Integer> newDNA;
      if (r.nextBoolean()) {
        newDNA = first.dna.subList(0, crossoverPoint);
        newDNA.addAll(second.dna.subList(crossoverPoint + 1, second.dna.size()));
      } else {
        newDNA = second.dna.subList(0, crossoverPoint);
        newDNA.addAll(first.dna.subList(crossoverPoint + 1, first.dna.size()));
      }

      return new Phrase(newDNA);
  }
  
  //...
}