Submit all code for code-java-string branch

2022-07-15 13:10:35 -04:00
parent c6df8af1e0
commit 27af9e2f8c
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+## Relevant Articles:
+
+- [Count Occurrences Using Java groupingBy Collector](https://www.baeldung.com/java-groupingby-count)
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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-streams-4</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-streams-4</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit</groupId>
+            <artifactId>junit-bom</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <type>pom</type>
+            <scope>import</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-streams-4</finalName>
+        <resources>
+            <resource>
+                <directory>src/main</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                    <compilerArgument>-parameters</compilerArgument>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <!-- testing -->
+        <maven-compiler-plugin.version>3.1</maven-compiler-plugin.version>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+
+</project>
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+package com.baeldung.streamcollectors;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class StreamGroupingByCollectorUnitTest {
+    @Test
+    public void givenListOfStrings_whenGroupingEqualStrings_thenUseCollectorsGroupingByToGroupEqualStringsAndCountOfOccurrences() {
+
+        List<String> list = new ArrayList<>(Arrays.asList("Foo", "Bar", "Bar", "Foo", "Bar"));
+
+        Map<String, Long> result = list.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
+        Assert.assertEquals(new Long(2), result.get("Foo"));
+        Assert.assertEquals(new Long(3), result.get("Bar"));
+
+    }
+
+    @Test
+    public void givenListOfStrings_whenGroupingEqualLengthStrings_thenUseCollectorsGroupingByConcurrentToGroupEqualLengthStringsAndCountOfOccurrences() {
+
+        List<String> list = new ArrayList<>(Arrays.asList("Adam", "Bill", "Jack", "Joe", "Ian"));
+
+        Map<Integer, Long> result = list.stream().collect(Collectors.groupingByConcurrent(String::length, Collectors.counting()));
+        Assert.assertEquals(new Long(2), result.get(3));
+        Assert.assertEquals(new Long(3), result.get(4));
+
+    }
+
+    @Test
+    public void givenListOfEmployees_whenGroupingDepartmentId_thenUseCollectorsGroupingByDepartmentIdAndCountNumberOfEmployeesWithinEveryDepartment() {
+
+        List<Employee> list = new ArrayList<>(Arrays.asList(new Employee(1, "Joe", 1), new Employee(2, "Josh", 1), new Employee(3, "Jamie", 2), new Employee(4, "Jim", 2), new Employee(5, "Jack", 2)));
+
+        Map<Integer, Long> result = list.stream().collect(Collectors.groupingBy(Employee::getDepartmentId, Collectors.counting()));
+        Assert.assertEquals(new Long(2), result.get(1));
+        Assert.assertEquals(new Long(3), result.get(2));
+
+    }
+
+    static class Employee {
+
+        Integer employeeId;
+        String employeeName;
+        Integer departmentId;
+
+        Employee(Integer employeeId, String employeeName, Integer departmentId) {
+            this.employeeId = employeeId;
+            this.employeeName = employeeName;
+            this.departmentId = departmentId;
+        }
+
+        public Integer getEmployeeId() {
+            return employeeId;
+        }
+
+        public void setEmployeeId(Integer employeeId) {
+            this.employeeId = employeeId;
+        }
+
+        public String getEmployeeName() {
+            return employeeName;
+        }
+
+        public void setEmployeeName(String employeeName) {
+            this.employeeName = employeeName;
+        }
+
+        public Integer getDepartmentId() {
+            return departmentId;
+        }
+
+        public void setDepartmentId(Integer departmentId) {
+            this.departmentId = departmentId;
+        }
+    }
+
+}