code: public void offset(int dx, int dy) {
          left += dx;
          top += dy;
          right += dx;
          bottom += dy;
      }
docs: Offset the rectangle by adding dx to its left and right coordinates, and
  adding dy to its top and bottom coordinates.
  
  @param dx The amount to add to the rectangle's left and right coordinates
  @param dy The amount to add to the rectangle's top and bottom coordinates