Oh, and here's my code:

import java.util.Scanner;
public class Test {

    public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    String input = sc.next();

    Boolean isItOne = true;
    int longestZero = 0;
    int longestOne = 0;
    int totalOnes = 0;

        while(input != null){

        int inputHex = Integer.parseInt (input, 16);
        String usBinary = Integer.toBinaryString(inputHex);
                       int stopCase = usBinary.length();

            while(stopCase > 0){

            String currentChar = usBinary.substring(0, stopCase);
            String test = currentChar.substring((stopCase - 1), stopCase);
            int testAsInt = Integer.parseInt(test);

                if(testAsInt == 1){
                totalOnes ++;
                }

            stopCase--;
            System.out.println(test);

            }

        input = sc.next();

        }

    System.out.println(totalOnes);
    }

}

If you don't do your own homework, you'll never learn anything.

Hint #1:  If something doesn't execute unless it's in a loop then it might
be reasonable to assume that the loop never exits ;)

Hint #2:  You might want to investigate how System.in works.

Suggestion #1:   Think about how you want your input to end and develop a
strategy therefrom.

Suggestion #2:  I could not follow your code because the indentation was out
of control.  This may be an error in cut and paste - but definitely try to
apply some organization if this is not the case.

later on "mmoski" <mmoski@gmail.com> said

Suggestion #3: Calm down.   It's going to be ok.   I think your question was
reasonable - but we are inundated with people who want us to do their
assignments for them - it puts everyone on the edge.   And it was obvious to
everyone that it was an assignment - regardless of any unique situation.

--
LTP