Method reference to an instance method

Let's assume that we are defining the following Comparator for Melon:

public class MelonComparator implements Comparator {

  @Override
  public int compare(Object m1, Object m2) {
    return Integer.compare(((Melon) m1).getWeight(),
      ((Melon) m2).getWeight());
  }
}

Now, we can refer to it as follows:

  • No method reference:
MelonComparator mc = new MelonComparator();

List<Melon> sorted = melons.stream()
  .sorted((Melon m1, Melon m2) -> mc.compare(m1, m2))
  .collect(Collectors.toList());
  • Method reference:
List<Melon> sorted = melons.stream()
  .sorted(mc::compare)
  .collect(Collectors.toList());

Of course, we can call Integer.compare() directly as well:

  • No method reference:
List<Integer> sorted = melons.stream()
  .map(m -> m.getWeight())
  .sorted((m1, m2) -> Integer.compare(m1, m2))
  .collect(Collectors.toList());
  • Method reference:
List<Integer> sorted = melons.stream()
  .map(m -> m.getWeight())
  .sorted(Integer::compare)
  .collect(Collectors.toList());
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