[java]Arrays.copyOf() VS System.arrayCopy()

If we want to copy an array, we can use either

System.arraycopy()

or

Arrays.copyOf()

. In this post, I use a simple example to demonstrate the difference between the two. 1. Simple Code Examples System.arraycopy()

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

int[] copied = new int[10];

System.arraycopy(arr, 0, copied, 1, 5);//5 is the length to copy

System.out.println(Arrays.toString(copied));

Output:

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

[0, 1, 2, 3, 4, 5, 0, 0, 0, 0]

Arrays.copyOf()

int[] copied = Arrays.copyOf(arr, 10); //10 the the length of the new array

System.out.println(Arrays.toString(copied));   copied = Arrays.copyOf(arr, 3);

System.out.println(Arrays.toString(copied));

Output:

[1, 2, 3, 4, 5, 0, 0, 0, 0, 0]

[1, 2, 3]

2. The Major Difference
The difference is that

Arrays.copyOf

does not only copy elements, it also creates a new array.

System.arrayCopy

copies into an existing array.
If we read the source code of Arrays.copyOf(), we can see that it uses

System.arraycopy()

.

public static int[] copyOf(int[] original, int newLength) {

int[] copy = new int[newLength];

System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength));

return copy;

}