怎样才能让我的jform铺满全屏呢

想知道该怎么才能平铺整个页面，应该写什么代码才能平铺整个页面啊

public static void main(String[] args) {
JFrame jf = new JFrame("屏幕尺寸");
jf.setLayout(null);
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
//获得屏幕得宽
int screenWidth = (int) screenSize.getWidth();
//获得屏幕得高
int screenHeight = (int) screenSize.getHeight();
jf.setSize(screenWidth, screenHeight);
jf.setVisible(true);
}