Something

class RoundedBorder implements Border {
        int radius;
        RoundedBorder(int radius) {
            this.radius = radius;
        }
        public Insets getBorderInsets(Component c) {
            return new Insets(this.radius+1, this.radius+1, this.radius+2, this.radius);
        }
        public boolean isBorderOpaque() {
            return true;
        }
        public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
            g.drawRoundRect(x,y,width-1,height-1,radius,radius);
        }
	}