As we've seen many times with recursion, a public method
often calls a private method that does the actual recursive work.
For binary search, the "make the problem smaller" part of the
recursive case involves looking at just a subsection of the array.
You can make this happen with this private method:
private int binSearch(int[] A, int key, int left, int right)
with the extra two parameters being the
leftmost and rightmost indicies of the array.
Thus, assuming the int myKey is the key, one would call
this method from the public method like this:
binSearch(A, myKey, 0, A.length-1);