Functional Programming in Java, 2nd Edition

Multiple and Fluent Comparisons

Let’s look at the convenience methods of the Comparator interface and use them to easily make comparisons based on multiple properties.

We’ll continue with the example from the previous section. To sort people by their name we used this:

people.stream()
      .sorted((person1, person2) ->
         person1.getName().compareTo(person2.getName()));

The syntax is concise compared to the inner-classes syntax from yesteryear. But we can do better thanks to convenience functions in the Comparator interface. We can more fluently express our objectives by using them. For example, to sort people by comparing their names, we can write this:

compare/fpij/Compare.java

final Function<Person, String> byName = person -> person.getName(); ...