Array Strange Postfix Evaluation

I have created an array of primitives and if i executes arr[index]++, then strange enough the content of my array is getting modified. Could someone explain why the content of array is getting modified. I am also pasting the sample code which illustrates the problem :

ExpectedOutput iArr[0] = 0 , tmpArr = [1, 2, 3]

ActualOutput iArr[0] = 1 , tmpArr = [1, 5, 3]

Sample Class:

class ArrayTest {
    public static void main(String args[]) {
        int i = 1;
        int[] iArr = { 0 };

        incr(iArr);

        System.out.println("iArr[0] = " + iArr[0]);

        int[] tmpArr = {1, 2, 3};

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


        System.out.println("tmpArr = " + Arrays.toString(tmpArr));

    }

    public static void incr(int[] n) {            
        n[0]++;
    }
}