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BAEL-9176 Code and Unit Tests for Converting Nested Loops to Streams in Java #18352

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BAEL-9176 Code and Unit Tests for Converting Nested Loops to Streams in Java #18352

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64 changes: 64 additions & 0 deletions ...core-java-streams-2/src/main/java/com/baeldung/streams/NestedLoopsToStreamsConverter.java
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package com.baeldung.streams;

import java.util.List;
import java.util.ArrayList;
import java.util.Optional;

import java.util.stream.Collectors;

public class NestedLoopsToStreamsConverter {

public static List<int[]> getAllPairsImperative(List<Integer> list1, List<Integer> list2) {
List<int[]> pairs = new ArrayList<>();
for (Integer num1 : list1) {
for (Integer num2 : list2) {
pairs.add(new int[] { num1, num2 });
}
}
return pairs;
}

public static List<int[]> getAllPairsStream(List<Integer> list1, List<Integer> list2) {
return list1.stream()
.flatMap(num1 -> list2.stream().map(num2 -> new int[] { num1, num2 }))
.collect(Collectors.toList());
}

public static List<int[]> getFilteredPairsImperative(List<Integer> list1, List<Integer> list2) {
List<int[]> pairs = new ArrayList<>();
for (Integer num1 : list1) {
for (Integer num2 : list2) {
if (num1 + num2 > 7) {
pairs.add(new int[] { num1, num2 });
}
}
}
return pairs;
}

public static List<int[]> getFilteredPairsStream(List<Integer> list1, List<Integer> list2) {
return list1.stream()
.flatMap(num1 -> list2.stream().map(num2 -> new int[] { num1, num2 }))
.filter(pair -> pair[0] + pair[1] > 7)
.collect(Collectors.toList());
}

public static Optional<int[]> getFirstMatchingPairImperative(List<Integer> list1, List<Integer> list2) {
for (Integer num1 : list1) {
for (Integer num2 : list2) {
if (num1 + num2 > 7) {
return Optional.of(new int[] { num1, num2 });
}
}
}
return Optional.empty();
}

public static Optional<int[]> getFirstMatchingPairStream(List<Integer> list1, List<Integer> list2) {
return list1.stream()
.flatMap(num1 -> list2.stream().map(num2 -> new int[] { num1, num2 }))
.filter(pair -> pair[0] + pair[1] > 7)
.findFirst();
}

}
51 changes: 51 additions & 0 deletions ...a-streams-2/src/test/java/com/baeldung/streams/NestedLoopsToStreamsConverterUnitTest.java
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package com.baeldung.streams;

import static org.junit.jupiter.api.Assertions.assertArrayEquals;
import static org.junit.Assert.assertEquals;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

import org.junit.Test;

public class NestedLoopsToStreamsConverterUnitTest {

@Test
public void givenTwoLists_whenGeneratingAllPairs_thenResultsShouldMatch() {
List<Integer> list1 = Arrays.asList(1, 2, 3);
List<Integer> list2 = Arrays.asList(4, 5, 6);

List<int[]> imperativeResult = NestedLoopsToStreamsConverter.getAllPairsImperative(list1, list2);
List<int[]> streamResult = NestedLoopsToStreamsConverter.getAllPairsStream(list1, list2);
assertEquals(imperativeResult.size(), streamResult.size());
for (int i = 0; i < imperativeResult.size(); i++) {
assertArrayEquals(imperativeResult.get(i), streamResult.get(i));
}
}

@Test
public void givenTwoLists_whenFilteringPairsBySum_thenResultsShouldMatch() {
List<Integer> list1 = Arrays.asList(1, 2, 3);
List<Integer> list2 = Arrays.asList(4, 5, 6);

List<int[]> imperativeResult = NestedLoopsToStreamsConverter.getFilteredPairsImperative(list1, list2);
List<int[]> streamResult = NestedLoopsToStreamsConverter.getFilteredPairsStream(list1, list2);
assertEquals(imperativeResult.size(), streamResult.size());
for (int i = 0; i < imperativeResult.size(); i++) {
assertArrayEquals(imperativeResult.get(i), streamResult.get(i));
}
}

@Test
public void givenTwoLists_whenFindingFirstMatchingPair_thenResultsShouldMatch() {
List<Integer> list1 = Arrays.asList(1, 2, 3);
List<Integer> list2 = Arrays.asList(4, 5, 6);

Optional<int[]> imperativeResult = NestedLoopsToStreamsConverter.getFirstMatchingPairImperative(list1, list2);
Optional<int[]> streamResult = NestedLoopsToStreamsConverter.getFirstMatchingPairStream(list1, list2);
assertEquals(imperativeResult.isPresent(), streamResult.isPresent());
imperativeResult.ifPresent(pair -> assertArrayEquals(pair, streamResult.get()));
}

}