Functional Programming in Java, 2nd Edition

Implementing the Comparator Interface

The Comparator interface is used in hundreds of places in the JDK library, from searching operations to sorting, reversing, and so on. This good old interface has turned into a functional interface; the benefit is that we can use charmingly fluent syntax to implement comparators.

Let’s create a few different implementations of the Comparator to understand the influence of the functional style. Our fingers will thank us for all the keystrokes saved by not having to create anonymous inner classes.

Sorting with a Comparator

We’ll build an example to sort a list of people using a few different points of comparison. Let’s first create the Person JavaBean.

compare/fpij/Person.java

public class Person {