Grouping by collector java (#10986)
* Initial Commit - Ports and Adapters * Restructured code to implement input and outbou ports and adapters * Added tests for groupingBy Collector * Revert "Initial Commit - Ports and Adapters" This reverts commit 55152dea * Added tests for groupingBy Collector * reverting * corrected typo * used BDD naming strategy for tests * Added a test for groupingByConcurrent * added new module and package * added core-java-streams-4 module in main pom.xml * updated pom.xml and changed artifactId
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devanshtrivedi5
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*.class
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0.*
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#folders#
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/target
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/neoDb*
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/data
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/src/main/webapp/WEB-INF/classes
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*/META-INF/*
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.resourceCache
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# Packaged files #
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*.jar
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*.war
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*.ear
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# Files generated by integration tests
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*.txt
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backup-pom.xml
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/bin/
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/temp
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#IntelliJ specific
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.idea/
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*.iml
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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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- [Count Occurrences using Java groupingBy Collector](https://baeldung.com/count-occurrences-with-java-groupingby-collector)
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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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-4</artifactId>
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<version>0.1.0-SNAPSHOT</version>
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<name>core-java-streams</name>
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<packaging>jar</packaging>
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<parent>
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<groupId>com.baeldung.core-java-modules</groupId>
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<artifactId>core-java-modules</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<relativePath>../</relativePath>
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</parent>
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<dependencies>
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<dependency>
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<groupId>log4j</groupId>
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<artifactId>log4j</artifactId>
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<version>${log4j.version}</version>
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</dependency>
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<dependency>
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<groupId>org.junit</groupId>
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<artifactId>junit-bom</artifactId>
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<version>${junit-jupiter.version}</version>
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<type>pom</type>
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<scope>import</scope>
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</dependency>
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</dependencies>
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<build>
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<finalName>core-java-streams-4</finalName>
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<resources>
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<resource>
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<directory>src/main</directory>
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<filtering>true</filtering>
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</resource>
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</resources>
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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-compiler-plugin</artifactId>
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<version>${maven-compiler-plugin.version}</version>
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<configuration>
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<source>${maven.compiler.source}</source>
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<target>${maven.compiler.target}</target>
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<compilerArgument>-parameters</compilerArgument>
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</configuration>
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</plugin>
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</plugins>
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</build>
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<properties>
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<!-- testing -->
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<maven-compiler-plugin.version>3.1</maven-compiler-plugin.version>
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<maven.compiler.source>1.8</maven.compiler.source>
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<maven.compiler.target>1.8</maven.compiler.target>
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</properties>
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</project>
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package com.baeldung.streamcollectors;
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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.Map;
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import java.util.function.Function;
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import java.util.stream.Collectors;
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import org.junit.Assert;
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import org.junit.Test;
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public class StreamGroupingByCollectorUnitTest
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{
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static class Employee {
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Integer employeeId;
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String employeeName;
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Integer departmentId;
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Employee(Integer employeeId, String employeeName, Integer departmentId) {
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this.employeeId = employeeId;
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this.employeeName = employeeName;
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this.departmentId = departmentId;
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}
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public Integer getEmployeeId() {
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return employeeId;
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}
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public void setEmployeeId(Integer employeeId) {
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this.employeeId = employeeId;
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}
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public String getEmployeeName() {
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return employeeName;
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}
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public void setEmployeeName(String employeeName) {
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this.employeeName = employeeName;
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}
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public Integer getDepartmentId() {
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return departmentId;
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}
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public void setDepartmentId(Integer departmentId) {
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this.departmentId = departmentId;
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}
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}
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@Test
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public void
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givenListOfStrings_whenGroupingEqualStrings_thenUseCollectorsGroupingByToGroupEqualStringsAndCountOfOccurrences() {
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List<String> list = new ArrayList<>(
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Arrays.asList("Foo", "Bar", "Bar", "Foo", "Bar")
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);
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Map<String, Long> result = list.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
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Assert.assertEquals(new Long(2), result.get("Foo"));
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Assert.assertEquals(new Long(3), result.get("Bar"));
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}
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@Test
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public void
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givenListOfStrings_whenGroupingEqualLengthStrings_thenUseCollectorsGroupingByConcurrentToGroupEqualLengthStringsAndCountOfOccurrences() {
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List<String> list = new ArrayList<>(
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Arrays.asList("Adam", "Bill", "Jack", "Joe", "Ian")
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);
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Map<Integer, Long> result = list.stream()
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.collect(Collectors.groupingByConcurrent(String::length, Collectors.counting()));
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Assert.assertEquals(new Long(2), result.get(3));
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Assert.assertEquals(new Long(3), result.get(4));
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}
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@Test
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public void
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givenListOfEmployees_whenGroupingDepartmentId_thenUseCollectorsGroupingByDepartmentIdAndCountNumberOfEmployeesWithinEveryDepartment() {
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List<Employee> list = new ArrayList<>(
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Arrays.asList(new Employee(1, "Joe", 1),
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new Employee(2, "Josh", 1),
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new Employee(3, "Jamie", 2),
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new Employee(4, "Jim", 2),
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new Employee(5, "Jack", 2))
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);
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Map<Integer, Long> result = list.stream() .collect(Collectors.groupingBy(Employee::getDepartmentId, Collectors.counting()));
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Assert.assertEquals(new Long(2), result.get(1));
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Assert.assertEquals(new Long(3), result.get(2));
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}
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}
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@ -0,0 +1,13 @@
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*.class
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#folders#
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/target
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/neoDb*
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/data
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/src/main/webapp/WEB-INF/classes
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*/META-INF/*
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# Packaged files #
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*.jar
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*.war
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*.ear
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@ -103,6 +103,7 @@
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<module>core-java-streams</module>
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<module>core-java-streams-2</module>
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<module>core-java-streams-3</module>
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<module>core-java-streams-4</module>
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<module>core-java-string-algorithms</module>
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<module>core-java-string-algorithms-2</module>
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<module>core-java-string-algorithms-3</module>
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