code: public String toShortString(StringBuilder sb) {
          sb.setLength(0);
          sb.append('[');
          sb.append(left);
          sb.append(',');
          sb.append(top);
          sb.append("][");
          sb.append(right);
          sb.append(',');
          sb.append(bottom);
          sb.append(']');
          return sb.toString();
      }
docs: Return a string representation of the rectangle in a compact form.
  
  @param sb sb
  
  @return string