java 显示单选按钮

package test;

import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

class MyRadio{
    private JFrame f=new JFrame("welcome to use!");
    private Container cont=f.getContentPane();
    private JRadioButton jb1=new JRadioButton("HJW");
    private JRadioButton jb2=new JRadioButton("ZK");
    private JRadioButton jb3=new JRadioButton("LJD");
    private JPanel pan=new JPanel();
    public MyRadio(){
        pan.setBorder(BorderFactory.createTitledBorder("Choose one Of belows:"));
        pan.setLayout(new GridLayout(1, 3));
        pan.add(this.jb1);
        pan.add(this.jb2);
        pan.add(this.jb3);
        cont.add(pan);
        this.f.setSize(330, 80);
        this.f.setVisible(true);
        this.f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent arg0){
                System.exit(1);
            }
        });
    }
}
public class test {
    public static void main(String[] args) {
        new MyRadio();
        
    }

}