dvd

public int compareTo(Vertex v) {
    final int BEFORE  = -1;
    final int AFTER = 1;
    final int EQUAL = 0;

    if (this == v) return EQUAL;

    if (this.y < v.y) {
      return BEFORE;
    } else {
      if (this.y == v.y) {
        if (this.x < v.x) {
          return BEFORE;
        } else {
          return AFTER;
        }
      } else {
        return AFTER;
      }
    }

  }