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.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.
CloneArray.java
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.
ArraysCopyOfMethod.java
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.
ArraysCopyOfRangeMethod.java
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)
SystemArrayCopy.java
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]
Note
Don’t forget to surround your code with try catch to handle Exceptions thrown
Don’t forget to surround your code with try catch to handle Exceptions thrown
References
About Author
Marilena Panagiotidou is a senior at University of the Aegean, in the department of Information and Communication Systems Engineering. She is passionate about programming in a wide range of languages. You can contact her at [email protected] or through her LinkedIn.
It was excellent.
Hi, how we can take the reference of JSON array? Can u help me?
Hello Manish, and thank you.
Let’s say you have the class Car and you create an Object for that class as follows:
Car myCar = new Car(“Toyota Avensis”);
Now let’s create another Car Object.
Car mySecondaryCar = new Car(“Toyota Yaris”);
If you type mySecondaryCar = myCar then your mySecondaryCar will now reference myCar and as a result it will have the value “Toyota Avensis” instead of “Toyota Yaris” that you declared when you created it.
You changed the reference and now it’s referencing exactly what myCar references.
Arrays in Java are Objects. So exactly the same thing happens to them too as shown in the Case 1.
I hope this helps you change your perspective of Arrays in Java and answers your question.
thank you
Very Nice Article, Can you please elaborate the case 1, and why we can not use
y= x;
in detail.
thank you