Split or move java-streams module
This commit is contained in:
catalin-burcea
11
core-java-modules/core-java-streams-3/README.md
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11
core-java-modules/core-java-streams-3/README.md
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## Core Java streams
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This module contains articles about the Stream API in Java.
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### Relevant Articles:
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- [The Difference Between map() and flatMap()](https://www.baeldung.com/java-difference-map-and-flatmap)
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- [How to Use if/else Logic in Java 8 Streams](https://www.baeldung.com/java-8-streams-if-else-logic)
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- [The Difference Between Collection.stream().forEach() and Collection.forEach()](https://www.baeldung.com/java-collection-stream-foreach)
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- [Guide to Java 8’s Collectors](https://www.baeldung.com/java-8-collectors)
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- [Primitive Type Streams in Java 8](https://www.baeldung.com/java-8-primitive-streams)
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- More articles: [[<-- prev>]](/../core-java-streams-2)
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53
core-java-modules/core-java-streams-3/pom.xml
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53
core-java-modules/core-java-streams-3/pom.xml
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<artifactId>core-java-streams-3</artifactId>
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<version>0.1.0-SNAPSHOT</version>
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<name>core-java-streams-3</name>
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<packaging>jar</packaging>
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<parent>
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<groupId>com.baeldung</groupId>
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<artifactId>parent-java</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<relativePath>../../parent-java</relativePath>
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</parent>
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<dependencies>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-lang3</artifactId>
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<version>${commons-lang3.version}</version>
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</dependency>
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<dependency>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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<version>${lombok.version}</version>
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<scope>provided</scope>
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</dependency>
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<!-- test scoped -->
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<dependency>
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<groupId>org.assertj</groupId>
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<artifactId>assertj-core</artifactId>
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<version>${assertj.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<finalName>core-java-streams-3</finalName>
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<resources>
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<resource>
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<directory>src/main/resources</directory>
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<filtering>true</filtering>
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</resource>
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</resources>
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</build>
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<properties>
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<!-- testing -->
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<assertj.version>3.6.1</assertj.version>
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<!-- plugins -->
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<maven-surefire-plugin.version>2.22.1</maven-surefire-plugin.version>
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</properties>
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</project>
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@@ -0,0 +1,84 @@
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package com.baeldung.streams.forEach;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.Iterator;
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import java.util.List;
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import java.util.function.Consumer;
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class ReverseList extends ArrayList<String> {
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List<String> list = Arrays.asList("A", "B", "C", "D");
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Consumer<String> removeElement = s -> {
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System.out.println(s + " " + list.size());
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if (s != null && s.equals("A")) {
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list.remove("D");
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}
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};
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@Override
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public Iterator<String> iterator() {
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final int startIndex = this.size() - 1;
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final List<String> list = this;
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return new Iterator<String>() {
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int currentIndex = startIndex;
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@Override
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public boolean hasNext() {
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return currentIndex >= 0;
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}
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@Override
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public String next() {
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String next = list.get(currentIndex);
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currentIndex--;
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return next;
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}
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@Override
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public void remove() {
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throw new UnsupportedOperationException();
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}
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};
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}
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public void forEach(Consumer<? super String> action) {
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for (String s : this) {
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action.accept(s);
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}
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}
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public void iterateParallel() {
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list.forEach(System.out::print);
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System.out.print(" ");
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list.parallelStream().forEach(System.out::print);
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}
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public void iterateReverse() {
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List<String> myList = new ReverseList();
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myList.addAll(list);
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myList.forEach(System.out::print);
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System.out.print(" ");
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myList.stream().forEach(System.out::print);
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}
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public void removeInCollectionForEach() {
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list.forEach(removeElement);
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}
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public void removeInStreamForEach() {
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list.stream().forEach(removeElement);
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}
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public static void main(String[] argv) {
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ReverseList collectionForEach = new ReverseList();
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collectionForEach.iterateParallel();
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collectionForEach.iterateReverse();
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collectionForEach.removeInCollectionForEach();
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collectionForEach.removeInStreamForEach();
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}
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}
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@@ -0,0 +1,23 @@
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package com.baeldung.streams.primitivestreams;
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import java.util.Arrays;
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import java.util.stream.IntStream;
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class PrimitiveStreams {
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int min(int[] integers) {
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return Arrays.stream(integers).min().getAsInt();
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}
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int max(int... integers) {
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return IntStream.of(integers).max().getAsInt();
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}
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int sum(int... integers) {
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return IntStream.of(integers).sum();
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}
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double avg(int... integers) {
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return IntStream.of(integers).average().getAsDouble();
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}
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}
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@@ -0,0 +1,13 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<configuration>
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<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
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<encoder>
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<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
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</pattern>
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</encoder>
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</appender>
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<root level="INFO">
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<appender-ref ref="STDOUT" />
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</root>
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</configuration>
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@@ -0,0 +1,231 @@
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package com.baeldung.streams.collectors;
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import com.google.common.collect.ImmutableList;
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import com.google.common.collect.ImmutableSet;
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import com.google.common.collect.Sets;
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import org.junit.Test;
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import java.util.Arrays;
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import java.util.Comparator;
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import java.util.DoubleSummaryStatistics;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Map;
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import java.util.Optional;
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import java.util.Set;
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import java.util.function.BiConsumer;
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import java.util.function.BinaryOperator;
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import java.util.function.Function;
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import java.util.function.Supplier;
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import java.util.stream.Collector;
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import static com.google.common.collect.Sets.newHashSet;
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import static java.util.stream.Collectors.averagingDouble;
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import static java.util.stream.Collectors.collectingAndThen;
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import static java.util.stream.Collectors.counting;
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import static java.util.stream.Collectors.groupingBy;
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import static java.util.stream.Collectors.joining;
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import static java.util.stream.Collectors.maxBy;
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import static java.util.stream.Collectors.partitioningBy;
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import static java.util.stream.Collectors.summarizingDouble;
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import static java.util.stream.Collectors.summingDouble;
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import static java.util.stream.Collectors.toCollection;
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import static java.util.stream.Collectors.toList;
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import static java.util.stream.Collectors.toMap;
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import static java.util.stream.Collectors.toSet;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.assertj.core.api.Assertions.assertThatThrownBy;
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public class Java8CollectorsUnitTest {
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private final List<String> givenList = Arrays.asList("a", "bb", "ccc", "dd");
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private final List<String> listWithDuplicates = Arrays.asList("a", "bb", "c", "d", "bb");
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@Test
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public void whenCollectingToList_shouldCollectToList() throws Exception {
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final List<String> result = givenList.stream().collect(toList());
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assertThat(result).containsAll(givenList);
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}
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@Test
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public void whenCollectingToSet_shouldCollectToSet() throws Exception {
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final Set<String> result = givenList.stream().collect(toSet());
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assertThat(result).containsAll(givenList);
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}
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@Test
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public void givenContainsDuplicateElements_whenCollectingToSet_shouldAddDuplicateElementsOnlyOnce() throws Exception {
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final Set<String> result = listWithDuplicates.stream().collect(toSet());
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assertThat(result).hasSize(4);
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}
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@Test
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public void whenCollectingToCollection_shouldCollectToCollection() throws Exception {
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final List<String> result = givenList.stream().collect(toCollection(LinkedList::new));
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assertThat(result).containsAll(givenList).isInstanceOf(LinkedList.class);
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}
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@Test
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public void whenCollectingToImmutableCollection_shouldThrowException() throws Exception {
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assertThatThrownBy(() -> {
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givenList.stream().collect(toCollection(ImmutableList::of));
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}).isInstanceOf(UnsupportedOperationException.class);
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}
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@Test
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public void whenCollectingToMap_shouldCollectToMap() throws Exception {
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final Map<String, Integer> result = givenList.stream().collect(toMap(Function.identity(), String::length));
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assertThat(result).containsEntry("a", 1).containsEntry("bb", 2).containsEntry("ccc", 3).containsEntry("dd", 2);
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}
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@Test
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public void whenCollectingToMapwWithDuplicates_shouldCollectToMapMergingTheIdenticalItems() throws Exception {
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final Map<String, Integer> result = listWithDuplicates.stream().collect(
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toMap(
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Function.identity(),
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String::length,
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(item, identicalItem) -> item
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)
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);
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assertThat(result).containsEntry("a", 1).containsEntry("bb", 2).containsEntry("c", 1).containsEntry("d", 1);
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}
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@Test
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public void givenContainsDuplicateElements_whenCollectingToMap_shouldThrowException() throws Exception {
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assertThatThrownBy(() -> {
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listWithDuplicates.stream().collect(toMap(Function.identity(), String::length));
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}).isInstanceOf(IllegalStateException.class);
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}
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@Test
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public void whenCollectingAndThen_shouldCollect() throws Exception {
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final List<String> result = givenList.stream().collect(collectingAndThen(toList(), ImmutableList::copyOf));
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assertThat(result).containsAll(givenList).isInstanceOf(ImmutableList.class);
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}
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@Test
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public void whenJoining_shouldJoin() throws Exception {
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final String result = givenList.stream().collect(joining());
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assertThat(result).isEqualTo("abbcccdd");
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}
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@Test
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public void whenJoiningWithSeparator_shouldJoinWithSeparator() throws Exception {
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final String result = givenList.stream().collect(joining(" "));
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assertThat(result).isEqualTo("a bb ccc dd");
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}
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@Test
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public void whenJoiningWithSeparatorAndPrefixAndPostfix_shouldJoinWithSeparatorPrePost() throws Exception {
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final String result = givenList.stream().collect(joining(" ", "PRE-", "-POST"));
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assertThat(result).isEqualTo("PRE-a bb ccc dd-POST");
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}
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@Test
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public void whenPartitioningBy_shouldPartition() throws Exception {
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final Map<Boolean, List<String>> result = givenList.stream().collect(partitioningBy(s -> s.length() > 2));
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assertThat(result).containsKeys(true, false).satisfies(booleanListMap -> {
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assertThat(booleanListMap.get(true)).contains("ccc");
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assertThat(booleanListMap.get(false)).contains("a", "bb", "dd");
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});
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}
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@Test
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public void whenCounting_shouldCount() throws Exception {
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final Long result = givenList.stream().collect(counting());
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assertThat(result).isEqualTo(4);
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}
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@Test
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public void whenSummarizing_shouldSummarize() throws Exception {
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final DoubleSummaryStatistics result = givenList.stream().collect(summarizingDouble(String::length));
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assertThat(result.getAverage()).isEqualTo(2);
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assertThat(result.getCount()).isEqualTo(4);
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assertThat(result.getMax()).isEqualTo(3);
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assertThat(result.getMin()).isEqualTo(1);
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assertThat(result.getSum()).isEqualTo(8);
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}
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@Test
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public void whenAveraging_shouldAverage() throws Exception {
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final Double result = givenList.stream().collect(averagingDouble(String::length));
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assertThat(result).isEqualTo(2);
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}
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@Test
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public void whenSumming_shouldSum() throws Exception {
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final Double result = givenList.stream().filter(i -> true).collect(summingDouble(String::length));
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assertThat(result).isEqualTo(8);
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}
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@Test
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public void whenMaxingBy_shouldMaxBy() throws Exception {
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final Optional<String> result = givenList.stream().collect(maxBy(Comparator.naturalOrder()));
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assertThat(result).isPresent().hasValue("dd");
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}
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@Test
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public void whenGroupingBy_shouldGroupBy() throws Exception {
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final Map<Integer, Set<String>> result = givenList.stream().collect(groupingBy(String::length, toSet()));
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assertThat(result).containsEntry(1, newHashSet("a")).containsEntry(2, newHashSet("bb", "dd")).containsEntry(3, newHashSet("ccc"));
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}
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@Test
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public void whenCreatingCustomCollector_shouldCollect() throws Exception {
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final ImmutableSet<String> result = givenList.stream().collect(toImmutableSet());
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assertThat(result).isInstanceOf(ImmutableSet.class).contains("a", "bb", "ccc", "dd");
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|
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}
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private static <T> ImmutableSetCollector<T> toImmutableSet() {
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return new ImmutableSetCollector<>();
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||||
}
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||||
private static class ImmutableSetCollector<T> implements Collector<T, ImmutableSet.Builder<T>, ImmutableSet<T>> {
|
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|
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@Override
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||||
public Supplier<ImmutableSet.Builder<T>> supplier() {
|
||||
return ImmutableSet::builder;
|
||||
}
|
||||
|
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@Override
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||||
public BiConsumer<ImmutableSet.Builder<T>, T> accumulator() {
|
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return ImmutableSet.Builder::add;
|
||||
}
|
||||
|
||||
@Override
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||||
public BinaryOperator<ImmutableSet.Builder<T>> combiner() {
|
||||
return (left, right) -> left.addAll(right.build());
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||||
}
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||||
|
||||
@Override
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||||
public Function<ImmutableSet.Builder<T>, ImmutableSet<T>> finisher() {
|
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return ImmutableSet.Builder::build;
|
||||
}
|
||||
|
||||
@Override
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||||
public Set<Characteristics> characteristics() {
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||||
return Sets.immutableEnumSet(Characteristics.UNORDERED);
|
||||
}
|
||||
}
|
||||
}
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||||
@@ -0,0 +1,41 @@
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||||
package com.baeldung.streams.conditional;
|
||||
|
||||
import java.util.Arrays;
|
||||
import java.util.List;
|
||||
import java.util.stream.Stream;
|
||||
|
||||
import org.junit.Assert;
|
||||
import org.junit.Test;
|
||||
|
||||
public class StreamForEachIfElseUnitTest {
|
||||
|
||||
@Test
|
||||
public final void givenIntegerStream_whenCheckingIntegerParityWithIfElse_thenEnsureCorrectParity() {
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||||
List<Integer> ints = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
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||||
|
||||
ints.stream()
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||||
.forEach(i -> {
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if (i.intValue() % 2 == 0) {
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||||
Assert.assertTrue(i.intValue() + " is not even", i.intValue() % 2 == 0);
|
||||
} else {
|
||||
Assert.assertTrue(i.intValue() + " is not odd", i.intValue() % 2 != 0);
|
||||
}
|
||||
});
|
||||
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenIntegerStream_whenCheckingIntegerParityWithStreamFilter_thenEnsureCorrectParity() {
|
||||
List<Integer> ints = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
|
||||
|
||||
Stream<Integer> evenIntegers = ints.stream()
|
||||
.filter(i -> i.intValue() % 2 == 0);
|
||||
Stream<Integer> oddIntegers = ints.stream()
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||||
.filter(i -> i.intValue() % 2 != 0);
|
||||
|
||||
evenIntegers.forEach(i -> Assert.assertTrue(i.intValue() + " is not even", i.intValue() % 2 == 0));
|
||||
oddIntegers.forEach(i -> Assert.assertTrue(i.intValue() + " is not odd", i.intValue() % 2 != 0));
|
||||
|
||||
}
|
||||
|
||||
}
|
||||
@@ -0,0 +1,93 @@
|
||||
package com.baeldung.streams.primitivestreams;
|
||||
|
||||
import org.junit.Test;
|
||||
|
||||
import java.util.List;
|
||||
import java.util.stream.Collectors;
|
||||
import java.util.stream.IntStream;
|
||||
import java.util.stream.Stream;
|
||||
|
||||
import static org.junit.Assert.assertEquals;
|
||||
import static org.junit.Assert.assertTrue;
|
||||
|
||||
public class PrimitiveStreamsUnitTest {
|
||||
|
||||
private PrimitiveStreams streams = new PrimitiveStreams();
|
||||
|
||||
@Test
|
||||
public void givenAnArrayOfIntegersWhenMinIsCalledThenCorrectMinIsReturned() {
|
||||
int[] integers = new int[] { 20, 98, 12, 7, 35 };
|
||||
int min = streams.min(integers); // returns 7
|
||||
|
||||
assertEquals(7, min);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnArrayOfIntegersWhenMaxIsCalledThenCorrectMaxIsReturned() {
|
||||
int max = streams.max(20, 98, 12, 7, 35);
|
||||
|
||||
assertEquals(98, max);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnArrayOfIntegersWhenSumIsCalledThenCorrectSumIsReturned() {
|
||||
int sum = streams.sum(20, 98, 12, 7, 35);
|
||||
|
||||
assertEquals(172, sum);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnArrayOfIntegersWhenAvgIsCalledThenCorrectAvgIsReturned() {
|
||||
double avg = streams.avg(20, 98, 12, 7, 35);
|
||||
|
||||
assertTrue(34.4 == avg);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenARangeOfIntegersWhenIntStreamSumIsCalledThenCorrectSumIsReturned() {
|
||||
int sum = IntStream.range(1, 10).sum();
|
||||
|
||||
assertEquals(45, sum);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenARangeClosedOfIntegersWhenIntStreamSumIsCalledThenCorrectSumIsReturned() {
|
||||
int sum = IntStream.rangeClosed(1, 10).sum();
|
||||
|
||||
assertEquals(55, sum);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenARangeWhenForEachIsCalledThenTheIndicesWillBePrinted() {
|
||||
IntStream.rangeClosed(1, 5).parallel().forEach(System.out::println);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnArrayWhenSumIsCalledThenTheCorrectSumIsReturned() {
|
||||
|
||||
int sum = Stream.of(33, 45).mapToInt(i -> i).sum();
|
||||
|
||||
assertEquals(78, sum);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnIntStreamThenGetTheEvenIntegers() {
|
||||
List<Integer> evenInts = IntStream.rangeClosed(1, 10).filter(i -> i % 2 == 0).boxed().collect(Collectors.toList());
|
||||
|
||||
List<Integer> expected = IntStream.of(2, 4, 6, 8, 10).boxed().collect(Collectors.toList());
|
||||
|
||||
assertEquals(expected, evenInts);
|
||||
}
|
||||
|
||||
class Person {
|
||||
private int age;
|
||||
|
||||
Person(int age) {
|
||||
this.age = age;
|
||||
}
|
||||
|
||||
int getAge() {
|
||||
return age;
|
||||
}
|
||||
}
|
||||
}
|
||||
Reference in New Issue
Block a user