code: @Override
      public void clearRect(int x, int y, int width, int height) {
          if (getBackground() == null) {
              return;  // we can't do anything
          }
          Paint saved = getPaint();
          setPaint(getBackground());
          fillRect(x, y, width, height);
          setPaint(saved);
      }
docs: Clears the specified rectangle by filling it with the current
  background color.  If the background color is {@code null}, this
  method will do nothing.
  
  @param x  the x-coordinate.
  @param y  the y-coordinate.
  @param width  the width.
  @param height  the height.
  
  @see #getBackground()