Functional Programming in Java, 2nd Edition

Refactoring Nested Loops

The imperative style code you see in this section was sent to me by a developer who was interested in applying functional programming and was curious to learn how to refactor it into the functional style. The code creates Pythagorean triples^[19] of positive numbers (a, b, c) which satisfy the condition a² + b² = c².

Let’s start with a few tests to verify the results of the compute method of a PythagoreanTriples class:

refactoring/fpij/PythagoreanTriplesTest.java

public class PythagoreanTriplesTest {
  PythagoreanTriples pythagoreanTriples;

  @BeforeEach
  public void init() {
    pythagoreanTriples = new PythagoreanTriples();
  }

  @Test
  public void compute() {
    assertAll(
 () -> assertEquals(List.of(), ...