// We want to have the ability to sort by zip code, and then break
// ties by using the enrolment.
import java.util.Comparator;

public class SchoolComparator implements Comparator
{
  public int compare(Object a, Object b)
  {
    int zip1 = ((School)a).getZip();
    int zip2 = ((School)b).getZip();
    int enrol1 = ((School)a).getEnrol();
    int enrol2 = ((School)b).getEnrol();

    // The goal is to return a negative if a < b,
    // return 0 if a == b, and return a positive if a > b.
    // In our comparison here, we look at ZIP code first.
    if (zip1 < zip2)
      return -1;
    else if (zip1 > zip2)
      return 1;
    else
    {
      if (enrol1 < enrol2)
        return -1;
      else if (enrol1 > enrol2)
        return 1;
      else
        return 0;
    }
  }
}