BAEL-2800_Copying_a_HashMap_in_Java new module added
This commit is contained in:
Anshul Bansal
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=========
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## Core Java Collections 2
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### Relevant Articles:
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- Java - Copying a HashMap
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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-collections-2</artifactId>
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<version>0.1.0-SNAPSHOT</version>
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<name>core-java-collections-2</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-collections4</artifactId>
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<version>${commons-collections4.version}</version>
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</dependency>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-lang3</artifactId>
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<version>${commons-lang3.version}</version>
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</dependency>
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<dependency>
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<groupId>org.eclipse.collections</groupId>
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<artifactId>eclipse-collections</artifactId>
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<version>${eclipse.collections.version}</version>
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</dependency>
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<dependency>
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<groupId>org.assertj</groupId>
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<artifactId>assertj-core</artifactId>
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<version>${assertj.version}</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.junit.platform</groupId>
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<artifactId>junit-platform-runner</artifactId>
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<version>${junit.platform.version}</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.openjdk.jmh</groupId>
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<artifactId>jmh-core</artifactId>
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<version>${openjdk.jmh.version}</version>
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</dependency>
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<dependency>
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<groupId>org.openjdk.jmh</groupId>
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<artifactId>jmh-generator-annprocess</artifactId>
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<version>${openjdk.jmh.version}</version>
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</dependency>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-exec</artifactId>
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<version>${commons-exec.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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</dependencies>
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<properties>
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<openjdk.jmh.version>1.19</openjdk.jmh.version>
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<junit.platform.version>1.2.0</junit.platform.version>
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<commons-lang3.version>3.8.1</commons-lang3.version>
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<commons-collections4.version>4.1</commons-collections4.version>
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<collections-generic.version>4.01</collections-generic.version>
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<avaitility.version>1.7.0</avaitility.version>
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<assertj.version>3.11.1</assertj.version>
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<eclipse.collections.version>7.1.0</eclipse.collections.version>
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<commons-exec.version>1.3</commons-exec.version>
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</properties>
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</project>
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package com.baeldung.copyinghashmap;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Set;
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import java.util.stream.Collectors;
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import org.apache.commons.lang3.SerializationUtils;
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public class CopyHashMap {
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public static HashMap basicCopy(HashMap originalMap, HashMap copyMap) {
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Set<Map.Entry> entries = originalMap.entrySet();
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for(Map.Entry mapEntry: entries) {
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copyMap.put(mapEntry.getKey(), mapEntry.getValue());
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}
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return copyMap;
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}
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public static Map copyUsingPutAll(Map originalMap, Map copyMap) {
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copyMap.putAll(originalMap);
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return copyMap;
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}
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public static HashMap copyUsingJava8Stream(HashMap originalMap) {
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Set<Map.Entry> entries = originalMap.entrySet();
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HashMap copyMap = (HashMap) entries
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.stream()
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.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
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return copyMap;
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}
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public static HashMap shallowCopy(HashMap originalMap) {
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//return new HashMap(originalMap);
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return (HashMap) originalMap.clone();
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}
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public static HashMap deepCopy(HashMap originalMap) {
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return SerializationUtils.clone(originalMap);
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}
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}
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+100
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package com.baeldung.copyinghashmap;
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import static org.junit.Assert.assertEquals;
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import static org.assertj.core.api.Assertions.assertThat;
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import java.util.HashMap;
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import java.util.Map;
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import org.junit.Test;
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import com.google.common.collect.ImmutableMap;
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public class CopyHashMapUnitTest {
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@Test
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public void givenHashmap_whenCopy_thenCopyContainsAllMappings() {
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HashMap<String, String> colorMap = new HashMap<>();
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colorMap.put("1", "Red");
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colorMap.put("2", "Blue");
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colorMap.put("3", "Green");
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System.out.println("ColorMap content : " + colorMap);
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HashMap<String, String> colorMapCopy = new HashMap<>();
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colorMapCopy.put("1", "Orange");
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colorMapCopy.put("4", "Black");
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colorMapCopy = CopyHashMap.basicCopy(colorMap, colorMapCopy);
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System.out.println("ColorMapCopy content : " +colorMapCopy);
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assertEquals(4, colorMapCopy.size());
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}
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@Test
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public void givenHashMap_whenShallowCopy_thenCopyisNotSameAsOriginal() {
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HashMap<String, Employee> employeeMap = new HashMap<>();
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Employee emp1 = new Employee("John", "Smith");
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Employee emp2 = new Employee("Norman", "Lewis");
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employeeMap.put("employee1",emp1);
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employeeMap.put("employee2",emp2);
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HashMap employeeMapShallowCopy = CopyHashMap.shallowCopy(employeeMap);
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assertThat(employeeMapShallowCopy).isNotSameAs(employeeMap);
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}
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@Test
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public void givenHashMap_whenShallowCopyModifyingOriginalObject_thenCopyShouldChange() {
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HashMap<String, Employee> employeeMap = new HashMap<>();
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Employee emp1 = new Employee("John", "Smith");
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Employee emp2 = new Employee("Norman", "Lewis");
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employeeMap.put("employee1",emp1);
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employeeMap.put("employee2",emp2);
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HashMap employeeMapShallowCopy = CopyHashMap.shallowCopy(employeeMap);
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emp1.setFirstName("Johny");
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assertThat(employeeMapShallowCopy.get("employee1"))
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.isEqualTo(employeeMap.get("employee1"));
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}
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@Test
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public void givenHashMap_whenDeepCopyModifyingOriginalObject_thenCopyShouldNotChange() {
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HashMap<String, Employee> employeeMap = new HashMap<>();
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Employee emp1 = new Employee("John", "Smith");
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Employee emp2 = new Employee("Norman", "Lewis");
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employeeMap.put("employee1",emp1);
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employeeMap.put("employee2",emp2);
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HashMap employeeMapDeepCopy = CopyHashMap.deepCopy(employeeMap);
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emp1.setFirstName("Johny");
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assertThat(employeeMapDeepCopy.get("employee1"))
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.isNotEqualTo(employeeMap.get("employee1"));
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}
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@Test
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public void givenImmutableMap_whenCopyUsingGuava_thenCopyShouldNotChange() {
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Map<String, Integer> heightMap = ImmutableMap.<String, Integer> builder()
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.put("emp1", 160)
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.put("emp2", 165)
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.put("emp3", 163)
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.build();
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Map<String, Integer> heightMapCopy = ImmutableMap.copyOf(heightMap);
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assertThat(heightMapCopy).isSameAs(heightMap);
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}
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}
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@@ -0,0 +1,38 @@
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package com.baeldung.copyinghashmap;
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import java.io.Serializable;
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public class Employee implements Serializable{
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private String firstName;
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private String lastName;
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public Employee(String firstName, String lastName) {
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super();
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this.firstName = firstName;
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this.lastName = lastName;
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}
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public String getFirstName() {
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return firstName;
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}
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public void setFirstName(String firstName) {
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this.firstName = firstName;
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}
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public String getLastName() {
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return lastName;
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}
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public void setLastName(String lastName) {
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this.lastName = lastName;
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}
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@Override
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public String toString() {
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return this.firstName + " " + this.lastName;
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}
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}
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