code: public void showCorner(boolean leftTop, boolean rightTop, boolean leftBottom, boolean rightBottom) {
          if (SDK_LOLLIPOP) {
              ((OptRoundRectDrawable) getBackground()).showCorner(leftTop, rightTop, leftBottom, rightBottom);
          } else {
              ((OptRoundRectDrawableWithShadow) getBackground()).showCorner(leftTop, rightTop, leftBottom, rightBottom);
          }
      }
docs: show corner or rect