insertion sort

I have the insertionSort method done. I am certain that it is proper. However, When I am trying to test it, I don't know what to pass in for the comparator argument. Please refer to the code below.

public static <T> void insertionSort(T[] a, Comparator <? super T> c)
	{
		for (int i = 1; i< a.length; i++)
		{
			T val = a[i];
			int j;
			for (j = i-1; j>=0; j-- )
			{
				if (c.compare(a[j], val) <= 0) break;
				a[j+1] = a[j];
			}
			a[j+1] = val;
		}
	}
//for testing
int[] num = {15, 3, 2, 9, 12, 83, 0};
AnagramUtil.insertionSort(num, c);//c is the comparator