code: public void setKnobStyle(final KnobStyle KNOB_STYLE) {
          getModel().setKnobStyle(KNOB_STYLE);
          init(getInnerBounds().width, getInnerBounds().height);
          repaint(getInnerBounds());
      }
docs: Sets the the style of the center knob of a radial gauge
  @param KNOB_STYLE