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.
HowNOTtoCopyAnArray.java
package com.favtuts.array;
import java.util.Arrays;
public class CopyArray {
public static void main(String[] args) {
HowNOTtoCopyAnArray();
}
static void HowNOTtoCopyAnArray() {
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.
CloneArray.java
package com.favtuts.array;
import java.util.Arrays;
public class CopyArray {
public static void main(String[] args) {
copyArrayByMethodObjectClone();
}
static void copyArrayByMethodObjectClone() {
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.
ArraysCopyOfMethod.java
package com.favtuts.array;
import java.util.Arrays;
public class CopyArray {
public static void main(String[] args) {
copyArrayWithArraysCopyOfMethod();
}
static void copyArrayWithArraysCopyOfMethod() {
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.
ArraysCopyOfRangeMethod.java
package com.favtuts.array;
import java.util.Arrays;
public class CopyArray {
public static void main(String[] args) {
copyArrayWithArraysCopyOfRangeMethod();
}
static void copyArrayWithArraysCopyOfRangeMethod() {
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)SystemArrayCopy.java
package com.favtuts.array;
import java.util.Arrays;
public class CopyArray {
public static void main(String[] args) {
copyArrayWithSystemArrayCopyMethod();
}
static void copyArrayWithSystemArrayCopyMethod() {
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]Note
Don’t forget to surround your code with try catch to handle Exceptions thrown
Download Source Code
$ git clone https://github.com/favtuts/java-core-tutorials-examples
$ cd java-basic/array