public int compareTo(Object o) {
   if (o instanceof LineBreakpointComparable) {
     LineBreakpoint lbthis = this;
     LineBreakpoint lb = (LineBreakpoint) o;
     int uc = lbthis.getURL().compareTo(lb.getURL());
     if (uc != 0) {
       return uc;
     } else {
       return lbthis.getLineNumber() - lb.getLineNumber();
     }
   } else {
     return -1;
   }
 }