Functional Programming in Java, 2nd Edition

Refactoring More Complex Loops

Traditional for loops allow us to increment or decrement the range by different step values. Let’s take a look at a countFrom1900 method of a LeapYears class that computes the number of leap years since 1900 to a given year.

Let’s start with the test first:

refactoring/fpij/LeapYearsTest.java

public class LeapYearsTest {
  LeapYears leapYears;

  @BeforeEach
  public void init() {
    leapYears = new LeapYears();
  }

  @Test
  public void countFrom1900() {
    assertAll(
      () -> assertEquals(25, leapYears.countFrom1900(2000)),
      () -> assertEquals(27, leapYears.countFrom1900(2010)),
      () -> assertEquals(31, leapYears.countFrom1900(2025)),
 () -> assertEquals(49, leapYears.countFrom1900(2100)), ...