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BAEL-9210: Stream Gatherers
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lines changed

10 files changed

+315
-3
lines changed

‎core-java-modules/core-java-streams-7/pom.xml‎

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@@ -35,8 +35,8 @@
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</build>
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<properties>
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<maven.compiler.source>12</maven.compiler.source>
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<maven.compiler.target>12</maven.compiler.target>
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<maven.compiler.source>24</maven.compiler.source>
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<maven.compiler.target>24</maven.compiler.target>
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<vavr.version>0.10.2</vavr.version>
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<assertj-core.version>3.23.1</assertj-core.version>
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<commons-lang3.version>3.12.0</commons-lang3.version>

‎core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/NumericSumGatherer.java‎

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package com.baeldung.streams.gatherer;
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import java.util.ArrayList;
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import java.util.function.BiConsumer;
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import java.util.function.Supplier;
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import java.util.stream.Gatherer;
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public class NumericSumGatherer implements Gatherer<Integer, ArrayList<Integer>, Integer> {
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@Override
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public Supplier<ArrayList<Integer>> initializer() {
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return ArrayList::new;
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}
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@Override
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public Integrator<ArrayList<Integer>, Integer, Integer> integrator() {
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return new Integrator<>() {
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@Override
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public boolean integrate(ArrayList<Integer> state, Integer element, Downstream<? super Integer> downstream) {
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if (state.isEmpty()) {
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state.add(element);
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} else {
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state.addFirst(state.getFirst() + element);
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}
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return true;
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}
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};
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}
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@Override
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public BiConsumer<ArrayList<Integer>, Downstream<? super Integer>> finisher() {
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return (state, downstream) -> {
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if (!downstream.isRejecting() && !state.isEmpty()) {
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downstream.push(state.getFirst());
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state.clear();
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}
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};
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}
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}

‎core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SentenceSplitterGatherer.java‎

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package com.baeldung.streams.gatherer;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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import java.util.function.BinaryOperator;
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import java.util.function.Supplier;
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import java.util.stream.Gatherer;
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public class SentenceSplitterGatherer implements Gatherer<String, List<String>,String> {
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@Override
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public Supplier<List<String>> initializer() {
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return ArrayList::new;
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}
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@Override
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public BinaryOperator<List<String>> combiner() {
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return (left, right) -> {
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left.addAll(right);
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return left;
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};
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}
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@Override
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public Integrator<List<String>, String, String> integrator() {
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return (state, element, downstream) -> {
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var words = element.split("\\s+");
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for (var word : words) {
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state.add(word);
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downstream.push(word);
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}
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return true;
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};
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}
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}

‎core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java‎

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package com.baeldung.streams.gatherer;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.function.BiConsumer;
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import java.util.function.Supplier;
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import java.util.stream.Gatherer;
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public class SlidingWindowGatherer implements Gatherer<Integer, ArrayList<Integer>, List<Integer>> {
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@Override
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public Supplier<ArrayList<Integer>> initializer() {
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return ArrayList::new;
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}
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@Override
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public Integrator<ArrayList<Integer>, Integer, List<Integer>> integrator() {
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return new Integrator<>() {
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@Override
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public boolean integrate(ArrayList<Integer> state, Integer element, Downstream<? super List<Integer>> downstream) {
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state.add(element);
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if (state.size() == 3) {
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downstream.push(new ArrayList<>(state));
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state.removeFirst();
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}
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return true;
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}
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};
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}
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@Override
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public BiConsumer<ArrayList<Integer>, Downstream<? super List<Integer>>> finisher() {
33+
return (state, downstream) -> {
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if (state.size()==3) {
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downstream.push(new ArrayList<>(state));
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}
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};
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}
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}

‎core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/GathererUnitTest.java‎

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package com.baeldung.streams.gatherer;
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import java.util.List;
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import java.util.stream.Gatherer;
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import java.util.stream.Gatherers;
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import java.util.stream.Stream;
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import org.junit.jupiter.api.Assertions;
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import org.junit.jupiter.api.Test;
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class GathererUnitTest {
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@Test
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void givenNumbers_whenFolded_thenSumIsEmitted() {
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Stream<Integer> numbers = Stream.of(1, 2, 3, 4, 5);
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Stream<Integer> folded = numbers.gather(Gatherers.fold(() -> 0, Integer::sum));
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List<Integer> resultList = folded.toList();
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Assertions.assertEquals(1, resultList.size());
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Assertions.assertEquals(Integer.valueOf(15), resultList.getFirst());
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}
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@Test
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void givenWords_whenMappedConcurrently_thenUppercasedWordsAreEmitted() {
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Stream<String> words = Stream.of("a", "b", "c", "d");
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List<String> resultList = words.gather(Gatherers.mapConcurrent(2, String::toUpperCase))
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.toList();
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Assertions.assertEquals(4, resultList.size());
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Assertions.assertEquals(List.of("A", "B", "C", "D"), resultList);
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}
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@Test
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void givenNumbers_whenScanned_thenRunningTotalsAreEmitted() {
33+
Stream<Integer> numbers = Stream.of(1, 2, 3, 4);
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List<Integer> resultList = numbers.gather(Gatherers.scan(() -> 0, Integer::sum))
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.toList();
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Assertions.assertEquals(4, resultList.size());
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Assertions.assertEquals(List.of(1, 3, 6, 10), resultList);
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}
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@Test
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void givenNumbers_whenWindowedSliding_thenOverlappingWindowsAreEmitted() {
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List<List<Integer>> expectedOutput = List.of(List.of(1, 2, 3), List.of(2, 3, 4), List.of(3, 4, 5));
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Stream<Integer> numbers = Stream.of(1, 2, 3, 4, 5);
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List<List<Integer>> resultList = numbers.gather(Gatherers.windowSliding(3))
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.toList();
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Assertions.assertEquals(3, resultList.size());
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Assertions.assertEquals(expectedOutput, resultList);
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}
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@Test
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void givenStrings_whenUsingCustomGatherer_thenLengthsAreCalculated() {
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List<Integer> expectedOutput = List.of(5, 6, 3);
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Stream<String> inputStrings = Stream.of("apple", "banana", "cat");
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List<Object> resultList = inputStrings.gather(Gatherer.of((state, element, downstream) -> {
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downstream.push(element.length());
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return true;
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}))
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.toList();
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Assertions.assertEquals(3, resultList.size());
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Assertions.assertEquals(expectedOutput, resultList);
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}
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}

‎core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/NumericSumGathererUnitTest.java‎

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package com.baeldung.streams.gatherer;
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import java.util.List;
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import java.util.stream.Stream;
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import org.junit.jupiter.api.Assertions;
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import org.junit.jupiter.api.Test;
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class NumericSumGathererUnitTest {
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@Test
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void givenNumbers_whenUsingCustomManyToOneGatherer_thenSumIsCalculated() {
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Stream<Integer> inputValues = Stream.of(1, 2, 3, 4, 5, 6);
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List<Integer> result = inputValues.gather(new NumericSumGatherer())
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.toList();
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Assertions.assertEquals(Integer.valueOf(21), result.getFirst());
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}
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}

‎core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SentenceSplitterGathererUnitTest.java‎

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package com.baeldung.streams.gatherer;
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import java.util.List;
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import java.util.stream.Stream;
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import org.junit.jupiter.api.Assertions;
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import org.junit.jupiter.api.Test;
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class SentenceSplitterGathererUnitTest {
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@Test
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void givenSentences_whenUsingCustomOneToManyGatherer_thenWordsAreExtracted() {
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List<String> expectedOutput = List.of("hello", "world", "java", "streams");
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Stream<String> sentences = Stream.of("hello world", "java streams");
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List<String> words = sentences.gather(new SentenceSplitterGatherer())
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.toList();
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Assertions.assertEquals(expectedOutput, words);
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}
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}

‎core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SlidingWindowGathererUnitTest.java‎

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package com.baeldung.streams.gatherer;
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import java.util.List;
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import java.util.stream.Stream;
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import org.junit.jupiter.api.Assertions;
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import org.junit.jupiter.api.Test;
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class SlidingWindowGathererUnitTest {
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@Test
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void givenNumbers_whenWindowedSliding_thenOverlappingWindowsAreEmitted() {
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List<List<Integer>> expectedOutput = List.of(List.of(1, 2, 3), List.of(2, 3, 4), List.of(3, 4, 5));
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Stream<Integer> numbers = Stream.of(1, 2, 3, 4, 5);
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List<List<Integer>> resultList = numbers.gather(new SlidingWindowGatherer())
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.toList();
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Assertions.assertEquals(3, resultList.size());
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Assertions.assertEquals(expectedOutput, resultList);
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}
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}

‎core-java-modules/pom.xml‎

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<module>core-java-streams-4</module>
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<module>core-java-streams-5</module>
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<module>core-java-streams-6</module>
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<module>core-java-streams-7</module>
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<!-- <module>core-java-streams-7</module> requires JDK 24-->
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<module>core-java-streams-collect</module>
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<module>core-java-streams-maps</module>
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<module>core-java-string-operations-3</module>

‎pom.xml‎

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</profile>
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<profile>
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<id>default-jdk24</id>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-surefire-plugin</artifactId>
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<configuration>
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<forkCount>3</forkCount>
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<reuseForks>true</reuseForks>
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<includes>
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<include>SpringContextTest</include>
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<include>**/*UnitTest</include>
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</includes>
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<excludes>
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<exclude>**/*IntegrationTest.java</exclude>
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<exclude>**/*IntTest.java</exclude>
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<exclude>**/*LongRunningUnitTest.java</exclude>
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<exclude>**/*ManualTest.java</exclude>
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<exclude>**/JdbcTest.java</exclude>
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<exclude>**/*LiveTest.java</exclude>
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</excludes>
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</configuration>
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</plugin>
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</plugins>
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</build>
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<modules>
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<module>core-java-modules/core-java-streams-7</module>
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</modules>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<java.version>24</java.version>
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<maven.compiler.source>24</maven.compiler.source>
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<maven.compiler.target>24</maven.compiler.target>
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<maven-pmd-plugin.version>3.26.0</maven-pmd-plugin.version>
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</properties>
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</profile>
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<profile>
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<id>integration-jdk17</id>
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<build>
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</profile>
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<profile>
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<id>integration-jdk24</id>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-surefire-plugin</artifactId>
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<version>${maven-surefire-plugin.version}</version>
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<configuration>
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<excludes>
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<exclude>**/*ManualTest.java</exclude>
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<exclude>**/*LiveTest.java</exclude>
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</excludes>
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<includes>
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<include>**/*IntegrationTest.java</include>
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<include>**/*IntTest.java</include>
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</includes>
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</configuration>
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</plugin>
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</plugins>
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</build>
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<modules>
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<module>core-java-modules/core-java-streams-7</module>
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</modules>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<java.version>24</java.version>
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<maven.compiler.source>24</maven.compiler.source>
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<maven.compiler.target>24</maven.compiler.target>
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<maven-pmd-plugin.version>3.26.0</maven-pmd-plugin.version>
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</properties>
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</profile>
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<profile>
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<id>live-all</id>
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<build>

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