Merge pull request #6652 from SmartyAnsh/master

BAEL-2800 -  BAEL-2800_Copying_a_HashMap_in_Java - new module added

core-java-collections-map/README.md

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+=========
+
+## Core Java Collections 2
+
+### Relevant Articles: 
+- Java - Copying a HashMap

core-java-collections-map/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" 
+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-collections-map</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-collections-map</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.collections</groupId>
+            <artifactId>eclipse-collections</artifactId>
+            <version>${eclipse.collections.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${openjdk.jmh.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${openjdk.jmh.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-exec</artifactId>
+            <version>${commons-exec.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <openjdk.jmh.version>1.19</openjdk.jmh.version>
+        <junit.platform.version>1.2.0</junit.platform.version>
+        <commons-lang3.version>3.8.1</commons-lang3.version>
+        <commons-collections4.version>4.1</commons-collections4.version>
+        <collections-generic.version>4.01</collections-generic.version>
+        <avaitility.version>1.7.0</avaitility.version>
+        <assertj.version>3.11.1</assertj.version>
+        <eclipse.collections.version>7.1.0</eclipse.collections.version>
+		<commons-exec.version>1.3</commons-exec.version>
+    </properties>
+</project>

core-java-collections-map/src/main/java/com/baeldung/copyinghashmap/CopyHashMap.java

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+package com.baeldung.copyinghashmap;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.apache.commons.lang3.SerializationUtils;
+
+public class CopyHashMap {
+    
+    public static <String, Employee> HashMap<String, Employee> copyUsingConstructor(HashMap<String, Employee> originalMap) {
+        return new HashMap<String, Employee>(originalMap);
+    }
+    
+    public static <String, Employee> HashMap<String, Employee> copyUsingClone(HashMap<String, Employee> originalMap) {
+        return (HashMap<String, Employee>) originalMap.clone();
+    }
+
+    public static <String, Employee> HashMap<String, Employee> copyUsingPut(HashMap<String, Employee> originalMap) {
+        HashMap<String, Employee> shallowCopy = new HashMap<String, Employee>();
+        Set<Entry<String, Employee>> entries = originalMap.entrySet();
+        for(Map.Entry<String, Employee> mapEntry: entries) {
+            shallowCopy.put(mapEntry.getKey(), mapEntry.getValue());
+        }
+        
+        return shallowCopy;
+    }
+    
+    public static <String, Employee> HashMap<String, Employee> copyUsingPutAll(HashMap<String, Employee> originalMap) {
+        HashMap<String, Employee> shallowCopy = new HashMap<String, Employee>();
+        shallowCopy.putAll(originalMap);
+        
+        return shallowCopy;
+    }
+    
+    public static <String, Employee> HashMap<String, Employee> copyUsingJava8Stream(HashMap<String, Employee> originalMap) {
+        Set<Entry<String, Employee>> entries = originalMap.entrySet();
+        HashMap<String, Employee> shallowCopy = (HashMap<String, Employee>) entries
+            .stream()
+            .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
+        
+        return shallowCopy;
+    }
+    
+    public static <String, Employee> HashMap<String, Employee> shallowCopy(HashMap<String, Employee> originalMap) {
+        return (HashMap<String, Employee>) originalMap.clone();
+    }
+    
+    public static <String, Employee> HashMap<String, Employee> deepCopy(HashMap<String, Employee> originalMap) {
+        return SerializationUtils.clone(originalMap);
+    }
+    
+}

core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/CopyHashMapUnitTest.java

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+package com.baeldung.copyinghashmap;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Test;
+
+import com.google.common.collect.ImmutableMap;
+
+public class CopyHashMapUnitTest {
+    
+    @Test
+    public void givenHashMap_whenShallowCopy_thenCopyisNotSameAsOriginal() {
+        
+        HashMap<String, Employee> map = new HashMap<>();
+        Employee emp1 = new Employee("John");
+        Employee emp2 = new Employee("Norman");
+        map.put("emp1",emp1);
+        map.put("emp2",emp2);
+    
+        HashMap<String, Employee> shallowCopy = CopyHashMap.shallowCopy(map);
+        
+        assertThat(shallowCopy).isNotSameAs(map);
+        
+    }
+    
+    @Test
+    public void givenHashMap_whenShallowCopyModifyingOriginalObject_thenCopyShouldChange() {
+        
+        HashMap<String, Employee> map = new HashMap<>();
+        Employee emp1 = new Employee("John");
+        Employee emp2 = new Employee("Norman");
+        map.put("emp1",emp1);
+        map.put("emp2",emp2);
+        
+        HashMap<String, Employee> shallowCopy = CopyHashMap.shallowCopy(map);
+        
+        emp1.setName("Johny");
+        
+        assertThat(shallowCopy.get("emp1")).isEqualTo(map.get("emp1"));
+        
+    }
+    
+    @Test
+    public void givenHashMap_whenDeepCopyModifyingOriginalObject_thenCopyShouldNotChange() {
+        
+        HashMap<String, Employee> map = new HashMap<>();
+        Employee emp1 = new Employee("John");
+        Employee emp2 = new Employee("Norman");
+        map.put("emp1",emp1);
+        map.put("emp2",emp2);
+        HashMap<String, Employee> deepCopy = CopyHashMap.deepCopy(map);
+        
+        emp1.setName("Johny");
+        
+        assertThat(deepCopy.get("emp1")).isNotEqualTo(map.get("emp1"));
+        
+    }
+    
+    @Test
+    public void givenImmutableMap_whenCopyUsingGuava_thenCopyShouldNotChange() {
+        Employee emp1 = new Employee("John");
+        Employee emp2 = new Employee("Norman");
+        
+        Map<String, Employee> map = ImmutableMap.<String, Employee> builder()
+            .put("emp1",emp1)
+            .put("emp2",emp2)
+            .build();
+        Map<String, Employee> shallowCopy = ImmutableMap.copyOf(map);
+        
+        assertThat(shallowCopy).isSameAs(map);
+        
+    }
+
+}

core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/Employee.java

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+package com.baeldung.copyinghashmap;
+
+import java.io.Serializable;
+
+public class Employee implements Serializable{
+    
+    private String name;
+    
+    public Employee(String name) {
+        super();
+        this.name = name;
+    }
+    public String getName() {
+        return name;
+    }
+    
+    public void setName(String name) {
+        this.name = name;
+    }
+    
+    @Override
+    public String toString() {
+        return this.name;
+    }
+ 
+}
+
+

pom.xml

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                 <!--<module>core-java-os</module> --> <!-- We haven't upgraded to java 9.-->
                 <module>core-java-arrays</module>
                 <module>core-java-collections</module>
+                <module>core-java-collections-map</module>
                 <module>core-java-collections-list</module>
                 <module>core-java-concurrency-basic</module>
                 <module>core-java-concurrency-collections</module>
@@ -1041,6 +1042,7 @@
                 <!--<module>core-java-os</module> --> <!-- We haven't upgraded to java 9.-->
                 <module>core-java-arrays</module>
                 <module>core-java-collections</module>
+                <module>core-java-collections-map</module>
                 <module>core-java-collections-list</module>
                 <module>core-java-concurrency-basic</module>
                 <module>core-java-concurrency-collections</module>