Java Copy Array - 4 Ways to copy from one to another Array

1. Overview

In this tutorial, You'll learn how to copy the array from one to another without loosing any values.

If you are new to java programming, learn how to create an array in java in various ways? 

Copying an array can be done in multiple ways. Let us discuss all possible ways.

Read the article till end to see best option for your case.

2. Copy Array Using Another Reference

Let us first create an array with 5 values and assign to a variable originalArray.

In the next step, create a new reference variable named "copiedArray" and assign the originalArray to copiedArray.

Further, printing the two arrays on the console using "Arrays.toString()" method.

import java.util.Arrays;

public class CopyArrayRefAssignment {

	public static void main(String[] args) {
		// creating an array

		int[] originalArray = { 1, 2, 3, 4, 5 };

		// assigning to the original array to new ref.
		int[] copiedArray = originalArray;

		// printing the arrays
		System.out.println("Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

		// changing the values in the original array

		originalArray[0] = 100;
		originalArray[4] = 500;

		// printing both arrays after modification

		System.out.println("\nPrinting values after original array modifications");
		System.out.println("Modified Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

	}

}

Output:

Original Array : [1, 2, 3, 4, 5]
Copied Array : [1, 2, 3, 4, 5]

Printing values after original array modifications
Modified Original Array : [100, 2, 3, 4, 500]
Copied Array : [100, 2, 3, 4, 500]

From the above output, you could see that originalArray and copiedArray have the same values.

But, we changed the values of original array using its index. After that printed the original and copied arrays. 

You might have noticed that copiedArray values are changed as per the modified original array.

Hence, it is not advisable to use the array assignment if original array is going to be modified in future because two references points to same object in the heap memory area.

3. Copy Array Using Iteration

Second approach is to iterate the array using for loop and assign each value to new array.

public class CopyArrayRefIterateExample {

	public static void main(String[] args) {
		// creating an array

		int[] originalArray = { 1, 2, 3, 4, 5 };

		// assigning to the original array to new ref.
		int[] copiedArray = new int[originalArray.length];

		// iterating array and assigning to the new array

		for (int i = 0; i < originalArray.length; i++) {
			copiedArray[i] = originalArray[i];
		}

		// printing the arrays
		System.out.println("Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

		// changing the values in the original array

		originalArray[0] = 100;
		originalArray[4] = 500;

		// printing both arrays after modification

		System.out.println("\nPrinting values after original array modifications");
		System.out.println("Modified Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

	}

}

Output:

Original Array : [1, 2, 3, 4, 5]
Copied Array : [1, 2, 3, 4, 5]

Printing values after original array modifications
Modified Original Array : [100, 2, 3, 4, 500]
Copied Array : [1, 2, 3, 4, 5]

In this approach, we need to copy the each value to new array. You can observe the output is that any changes to the original array does not affect the copied array.

4. Copy Array Using Clone Approach

Next third approach, you'll see the example program using clone() method. You can understand the differences between deep copy vs shallow copy cloning in java.

public class CopyArrayCloneExample {

	public static void main(String[] args) {
		// creating an array

		int[] originalArray = { 1, 2, 3, 4, 5 };

		// cloning array using clone() method
		int[] copiedArray = originalArray.clone();
		

		// printing the arrays
		System.out.println("Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

		// changing the values in the original array

		originalArray[0] = 100;
		originalArray[4] = 500;

		// printing both arrays after modification

		System.out.println("\nPrinting values after original array modifications");
		System.out.println("Modified Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

	}

}

Output:

Original Array : [1, 2, 3, 4, 5]
Copied Array : [1, 2, 3, 4, 5]

Printing values after original array modifications
Modified Original Array : [100, 2, 3, 4, 500]
Copied Array : [1, 2, 3, 4, 5]

This approach works fine as similar to the above approach.

5. Copy Array Using System.arraycopy() Method

In the last approach, you'll use the System.arraycopy() method which does copy the values from original array for a given index range.

public class CopyArraySystemArraycopyExample {

	public static void main(String[] args) {
		// creating an array

		int[] originalArray = { 1, 2, 3, 4, 5 };

		// Creating a new array as same as original. 
		int[] copiedArray = new int[originalArray.length];

		// cloning array using clone() method
		System.arraycopy(originalArray, 0, copiedArray, 0, originalArray.length);

		// printing the arrays
		System.out.println("Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

		// changing the values in the original array

		originalArray[0] = 100;
		originalArray[4] = 500;

		// printing both arrays after modification

		System.out.println("\nPrinting values after original array modifications");
		System.out.println("Modified Original Array : " + Arrays.toString(originalArray));

		System.out.println("Copied Array : " + Arrays.toString(copiedArray));

	}

}

This approach also work well and could see it as used in many collections api internally.

Hence, this approach is better choice if you want to copy the large data set which is stored in array.

6. Conclusion

In this article, you've seen the various ways to copy array to another in java.

GitHub sample code

CopyArrayRefAssignment

CopyArrayRefIterateExample

CopyArrayCloneExample

CopyArraySystemArraycopyExample

Ref