# Functional Programming in Java, Second Edition: Functional Programming in Java, Second Edition: JUnit code improvements for Chapter 11, pages 195 ff “Refactoring Nested Loops"

Nothing surprising here, just adapting the form to the other examples.

Ah yes, `compute()` now returns an immutable list in all cases.

``````package chapter11;

import org.junit.jupiter.api.Test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.assertAll;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class NestedLoopTest {

record Triple(int a, int b, int c) {
public String toString() {
return String.format("%d %d %d", a, b, c);
}
}

private static Triple triple(int a, int b, int c) {
return new Triple(a, b, c);
}

interface PythagoreanTriples {
List<Triple> compute(int numberOfValues);
}

// (m² - n², 2 * m * n, m² + n²) is a valid triple because, resolving
// (m⁴ + n⁴ - 2 * m² * n²) + (4 * m² * n²) = m⁴ + n⁴ + 2 * m² * n²
// assuming m > n

private static Triple getTripleEuclidsWay(final int m, final int n) {
if (m <= n) {
throw new IllegalArgumentException("m <= n");
}
final int a = m * m - n * n;
final int b = 2 * m * n;
final int c = m * m + n * n;
return triple(a, b, c);
}

static class PythagoreanTriplesBefore implements PythagoreanTriples {

public List<Triple> compute(int tripleCount) {
if (tripleCount == 0) {
return List.of(); // unmodifiable
}
List<Triple> triples = new ArrayList<>();
for (int m = 2; ; m++) {
for (int n = 1; n < m; n++) {
if (triples.size() == tripleCount)
break;
}
if (triples.size() == tripleCount)
break;
}
return Collections.unmodifiableList(triples);
}
}

static class PythagoreanTriplesAfter implements PythagoreanTriples {

public List<Triple> compute(int tripleCount) {
return Stream.iterate(2, e -> e + 1)
.flatMap(m -> IntStream.range(1, m).mapToObj(n -> getTripleEuclidsWay(m, n)))
.limit(tripleCount)
.toList();
}

}

private static void commonPythagoreanTriplesTests(final PythagoreanTriples pytris) {
assertAll(
() -> assertEquals(List.of(), pytris.compute(0)),
() -> assertEquals(List.of(triple(3, 4, 5)),
pytris.compute(1)),
() -> assertEquals(
List.of(triple(3, 4, 5), triple(8, 6, 10), triple(5, 12, 13)),
pytris.compute(3)),
() -> assertEquals(
List.of(triple(3, 4, 5), triple(8, 6, 10),
triple(5, 12, 13), triple(15, 8, 17),
triple(12, 16, 20)),
pytris.compute(5))
);
}

@Test
void pythagoreanTriplesBefore() {
commonPythagoreanTriplesTests(new PythagoreanTriplesBefore());
}

@Test
void pythagoreanTriplesAfter() {
commonPythagoreanTriplesTests(new PythagoreanTriplesAfter());
}
}
``````