code: private static int indexOf(String source, String target, 
          int startIndex, IntBinaryOperator comparator)
      {
          return indexOf(
              source, 0, source.length(), 
              target, 0, target.length(), 
              startIndex, comparator);
      }
docs: Returns the index of the first appearance of the given target in
  the given source, starting at the given index, using the given
  comparator for characters. Returns -1 if the target string is
  not found.
  
  @param source The source string
  @param target The target string
  @param startIndex The start index
  @param comparator The comparator
  @return The index