Java: System.arraycopy for 2 parts of array

Question

Suppose I have an array declared as

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

and I want to create a new array, a, with a size 25% greater than that of unordered which has the original contents in order, followed by the indices that have not yet been assigned a value (ie 1, 2, 3, 4, 5, 0, 0, 0). How would I do this using System.arraycopy? Currently, what I have is:

int[] a = new int[(int)(unordered.length*.25)];
System.arraycopy(items, 3, a, 0, unordered.length-3);
System.arraycopy(items, 0, a, unordered.length-3, 3);

When I run this code, I get an array out of bounds error.

Answer 1

Change this:

int[] a = new int[(int)(unordered.length*.25)];

To:

int[] a = new int[(int)(unordered.length*1.25) + 1];

As int cast is lowering the number (for example 3.5 -> 3 etc.) you should add one to the array size.

Also multiply by 1.25 in order to increase the array size as multiply by 0.25 is decreasing the size.