Functional Programming in Java, 2nd Edition

Creating Fluent Interfaces Using Lambda Expressions

We’ve been looking at the internals of methods and classes in this chapter. Now let’s shift our focus to see how lambda expressions can help shape a class’s skin or interface. We can use these techniques to structure the API of our classes to make it more intuitive and fluent for programmers to use.

Starting with a Design

Let’s start with a simple Mailer class and evolve the design of its interface.

designing/fpij/Mailer.java

public class Mailer {
  public void from(final String address) { /*... */ }
  public void to(final String address)   { /*... */ }
  public void subject(final String line) { /*... */ }
  public void body(final String message) {