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 (i.e. 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.

Multiply by 1.25 in order to make the array 25% larger. Right now you are making it smaller. — castletheperson
– castletheperson, Commented Feb 2, 2017 at 22:52

omri_saadon · Accepted Answer · 2017-02-02 22:52:01Z

5

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.

answered Feb 2, 2017 at 22:52

omri_saadon

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1 Comment

nbarrell Over a year ago

I also just realized I had to multiply by 1.25 and not 0.25-- silly mistake. Thank you, it works now!

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