How to copy an Array in Java

The methods described below are only applicable to one dimensional arrays. Before we talk about the different ways to copy an array in Java we will show you how NOT to copy an Array.

How NOT to copy an Array in Java

Arrays in Java are Objects. If you try to treat them as variables… well you can(!) but what you are really copying is the reference!. The example below explains this statement.

package com.mkyong.copyarray;
import java.util.Arrays;
public class HowNOTtoCopyAnArray {
	public static void main(String[] args){
		int[] x = {1, 2, 3, 4, 5};
		int[] y = x; //don't copy array like this!
		System.out.println(Arrays.toString(x));
		System.out.println(Arrays.toString(y)+"\n");
		x[1] = 22; // y[1] will display 22! same reference
		System.out.println(Arrays.toString(x));
		System.out.println(Arrays.toString(y)+"\n");
		y[4] = 55; // x[4] will display 55!
		System.out.println(Arrays.toString(x));
		System.out.println(Arrays.toString(y));

Output:

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
[1, 22, 3, 4, 5]
[1, 22, 3, 4, 5]
[1, 22, 3, 4, 55]
[1, 22, 3, 4, 55]

1. Object.clone()

Arrays inherit methods from Object class, and clone is one of them. If you need to copy an Array as it is then this is the method you should use.

package com.mkyong.copyarray;
import java.util.Arrays;
public class CloneArray {
	public static void main(String[] args){
		int[] x = {1, 2, 3, 4, 5};
		int[] y = x.clone();
		System.out.println(Arrays.toString(x));
		System.out.println(Arrays.toString(y)+"\n");
		x[1] = 22;
		System.out.println(Arrays.toString(x));
		System.out.println(Arrays.toString(y)+"\n");
		y[4] = 55;
		System.out.println(Arrays.toString(x));
		System.out.println(Arrays.toString(y));

Output:

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
[1, 22, 3, 4, 5]
[1, 2, 3, 4, 5]
[1, 22, 3, 4, 5]
[1, 2, 3, 4, 55]

2. Arrays.copyOf()

In Arrays class there are two methods that copy an array fully or partially. Here’s an example of copyOf() method.

package com.mkyong.copyarray;
import java.util.Arrays;
public class ArraysCopyOfMethod {
	public static void main(String[] args){
		String[] x = {"one", "two", "three", "four", "five"};
		String[] y = Arrays.copyOf(x, x.length);
		String[] z = Arrays.copyOf(x, 3); //will copy the 3 first elements of array x
		System.out.println("Array x: " + Arrays.toString(x));
		System.out.println("Array y: " + Arrays.toString(y));
		System.out.println("Array z: " + Arrays.toString(z));

Output:

Array x: [one, two, three, four, five]
Array y: [one, two, three, four, five]
Array z: [one, two, three]

3. Arrays.copyOfRange()

And this is an example of copyOfRange() method.

package com.mkyong.copyarray;
import java.util.Arrays;
public class ArraysCopyOfRangeMethod {
	public static void main(String[] args){
		String[] x = {"one", "two", "three", "four", "five"};
		String[] y = Arrays.copyOfRange(x, 0, x.length); //full copy of the array
		String[] z = Arrays.copyOfRange(x, x.length-2, x.length); //copy only the last 2 elements
		System.out.println("Array x: " + Arrays.toString(x));
		System.out.println("Array y: " + Arrays.toString(y));
		System.out.println("Array z: " + Arrays.toString(z));

Output:

Array x: [one, two, three, four, five]
Array y: [one, two, three, four, five]
Array z: [four, five]

4. System.arraycopy()

With System.arraycopy() you can control the range of elements from the source array that you want to copy,
and the destined position.

Review the System.arraycopy signature (JavaDoc) :

arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

package com.mkyong.copyarray;
import java.util.Arrays;
public class SystemArrayCopy {
	public static void main(String[] args){
		String[] x = {"one", "two", "three", "four", "five"};
		String[] y = new String[2];
		System.arraycopy(x, 3, y, 0, 2);
		System.out.println("Array x: " + Arrays.toString(x));
		System.out.println("Array y: " + Arrays.toString(y) + "\n");
		Object[] z = new Object[5];
		System.arraycopy(x, 0, z, 0, 5);
		System.out.println("Array z: " + Arrays.toString(z)+"\n");
		Integer[] w = {3, 4, 5};
		System.out.println("Array w: " + Arrays.toString(w));
		//copy from the second value (1) of array w to z and place in the fourth place (3) the 2 values 
		System.arraycopy(w, 1, z, 3, 2); 
		System.out.println("Array z: " + Arrays.toString(z));

Output:

Array x: [one, two, three, four, five]
Array y: [four, five]
Array z: [one, two, three, four, five]
Array w: [3, 4, 5]
Array z: [one, two, three, 4, 5]

References

1. Arrays JavaDoc
2. System JavaDoc
3. How to Copy Arrays in Java