(BAEL-746) How to Copy an Array in Java (#1474)

core-java/src/main/java/com/baeldung/arraycopy/model/Address.java

@@ -0,0 +1,61 @@
+package com.baeldung.arraycopy.model;
+
+public class Address implements Cloneable {
+    private String country;
+    private String state;
+    private String city;
+    private String street;
+    private String zipcode;
+
+    public String getCountry() {
+        return country;
+    }
+
+    public void setCountry(String country) {
+        this.country = country;
+    }
+
+    public String getState() {
+        return state;
+    }
+
+    public void setState(String state) {
+        this.state = state;
+    }
+
+    public String getCity() {
+        return city;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public String getStreet() {
+        return street;
+    }
+
+    public void setStreet(String street) {
+        this.street = street;
+    }
+
+    public String getZipcode() {
+        return zipcode;
+    }
+
+    public void setZipcode(String zipcode) {
+        this.zipcode = zipcode;
+    }
+
+    @Override
+    protected Object clone() throws CloneNotSupportedException {
+        super.clone();
+        Address address = new Address();
+        address.setCity(this.city);
+        address.setCountry(this.country);
+        address.setState(this.state);
+        address.setStreet(this.street);
+        address.setZipcode(this.zipcode);
+        return address;
+    }
+}

core-java/src/main/java/com/baeldung/arraycopy/model/Employee.java

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+package com.baeldung.arraycopy.model;
+
+import java.io.Serializable;
+
+public class Employee implements Serializable {
+    private static final long serialVersionUID = -2454619097207585825L;
+    private int id;
+    private String name;
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}

core-java/src/test/java/com/baeldung/arraycopy/ArrayCopyUtilTest.java

@@ -0,0 +1,163 @@
+package com.baeldung.arraycopy;
+
+import com.baeldung.arraycopy.model.Address;
+import com.baeldung.arraycopy.model.Employee;
+import org.apache.commons.lang3.SerializationUtils;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.Arrays;
+
+public class ArrayCopyUtilTest {
+    private static Employee[] employees;
+    private static final int MAX = 2;
+
+    @BeforeClass
+    public static void setup(){
+      employees = new Employee[MAX];
+      Employee employee;
+      for(int i = 0; i < MAX; i++) {
+          employee = new Employee();
+          employee.setName("Emp"+i);
+          employee.setId(i);
+          employees[i] = employee;
+      }
+    }
+
+    @Test
+    public void givenArrayOfPrimitiveType_whenCopiedViaSystemsArrayCopy_thenSuccessful(){
+        int[] array = {23, 43, 55};
+        int[] copiedArray = new int[3];
+        
+        System.arraycopy(array, 0, copiedArray, 0, 3);
+        
+        Assert.assertTrue(array.length == copiedArray.length);
+        Assert.assertTrue(copiedArray[0] == array[0]);
+        Assert.assertTrue(copiedArray[1] == array[1]);
+        Assert.assertTrue(copiedArray[2] == array[2]);
+    }
+
+    @Test
+    public void givenArrayOfPrimitiveType_whenCopiedSubSequenceViaSystemsArrayCopy_thenSuccessful(){
+        int[] array = {23, 43, 55, 12, 65, 88, 92};
+        int[] copiedArray = new int[3];
+        
+        System.arraycopy(array, 2, copiedArray, 0, 3);
+        
+        Assert.assertTrue(3 == copiedArray.length);
+        Assert.assertTrue(copiedArray[0] == array[2]);
+        Assert.assertTrue(copiedArray[1] == array[3]);
+        Assert.assertTrue(copiedArray[2] == array[4]);
+    }
+
+    @Test
+    public void givenArrayOfPrimitiveType_whenCopiedSubSequenceViaArraysCopyOfRange_thenSuccessful(){
+        int[] array = {23, 43, 55, 12, 65, 88, 92};
+        
+        int[] copiedArray = Arrays.copyOfRange(array, 1, 4);
+        
+        Assert.assertTrue(3 == copiedArray.length);
+        Assert.assertTrue(copiedArray[0] == array[1]);
+        Assert.assertTrue(copiedArray[1] == array[2]);
+        Assert.assertTrue(copiedArray[2] == array[3]);
+    }
+
+    @Test
+    public void givenArrayOfPrimitiveType_whenCopiedViaArraysCopyOf_thenValueChangeIsSuccessful(){
+        int[] array = {23, 43, 55, 12};
+        int newLength = array.length;
+        
+        int[] copiedArray = Arrays.copyOf(array, newLength);
+        
+        Assert.assertNotNull(copiedArray);
+        Assert.assertTrue(copiedArray.length == array.length);
+        Assert.assertTrue(copiedArray[0] == array[0]);
+        Assert.assertTrue(copiedArray[1] == array[1]);
+        Assert.assertTrue(copiedArray[2] == array[2]);
+        Assert.assertTrue(copiedArray[3] == array[3]);
+        array[0] = 9;
+        Assert.assertTrue(copiedArray[0] != array[0]);
+        copiedArray[1] = 12;
+        Assert.assertTrue(copiedArray[1] != array[1]);
+    }
+
+    @Test
+    public void givenArrayOfNonPrimitiveType_whenCopiedViaArraysCopyOf_thenDoShallowCopy(){
+        Employee[] copiedArray = Arrays.copyOf(employees, employees.length);
+        
+        Assert.assertNotNull(copiedArray);
+        Assert.assertTrue(copiedArray.length == employees.length);
+        employees[0].setName(employees[0].getName()+"_Changed");
+        //change in employees' element caused change in the copied array
+        Assert.assertTrue(copiedArray[0].getName().equals(employees[0].getName()));
+    }
+
+    @Test
+    public void givenArrayOfPrimitiveType_whenCopiedViaArrayClone_thenValueChangeIsSuccessful(){
+        int[] array = {23, 43, 55, 12};
+        
+        int[] copiedArray = array.clone();
+        
+        Assert.assertNotNull(copiedArray);
+        Assert.assertTrue(copiedArray.length == array.length);
+        Assert.assertTrue(copiedArray[0] == array[0]);
+        Assert.assertTrue(copiedArray[1] == array[1]);
+        Assert.assertTrue(copiedArray[2] == array[2]);
+        Assert.assertTrue(copiedArray[3] == array[3]);
+        array[0] = 9;
+        Assert.assertTrue(copiedArray[0] != array[0]);
+        copiedArray[1] = 12;
+        Assert.assertTrue(copiedArray[1] != array[1]);
+    }
+
+    @Test
+    public void givenArraysOfNonPrimitiveType_whenCopiedViaArrayClone_thenDoShallowCopy(){
+        Employee[] copiedArray = employees.clone();
+        
+        Assert.assertNotNull(copiedArray);
+        Assert.assertTrue(copiedArray.length == employees.length);
+        employees[0].setName(employees[0].getName()+"_Changed");
+        //change in employees' element changed the copied array
+        Assert.assertTrue(copiedArray[0].getName().equals(employees[0].getName()));
+    }
+
+    @Test
+    public void givenArraysOfCloneableNonPrimitiveType_whenCopiedViaArrayClone_thenDoShallowCopy(){
+        Address[] addresses = createAddressArray();
+        
+        Address[] copiedArray = addresses.clone();
+        
+        Assert.assertNotNull(copiedArray);
+        Assert.assertTrue(copiedArray.length == addresses.length);
+        addresses[0].setCity(addresses[0].getCity()+"_Changed");
+        Assert.assertTrue(copiedArray[0].getCity().equals(addresses[0].getCity()));
+    }
+
+    @Test
+    public void givenArraysOfSerializableNonPrimitiveType_whenCopiedViaSerializationUtils_thenDoDeepCopy(){
+        Employee[] copiedArray = SerializationUtils.clone(employees);
+        
+        Assert.assertNotNull(copiedArray);
+        Assert.assertTrue(copiedArray.length == employees.length);
+        employees[0].setName(employees[0].getName()+"_Changed");
+        //change in employees' element didn't change in the copied array
+        Assert.assertFalse(copiedArray[0].getName().equals(employees[0].getName()));
+    }
+
+    private Address[] createAddressArray(){
+        Address[] addresses = new Address[1];
+        addresses[0] = createAddress();
+        return addresses;
+    }
+
+    private Address createAddress() {
+        Address address = new Address();
+        address.setCountry("USA");
+        address.setState("CA");
+        address.setCity("San Francisco");
+        address.setStreet("Street 1");
+        address.setZipcode("59999");
+        return address;
+    }
+}