jf.setResizable(false);

jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//設置窗體關閉時，退出程序

另：
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);也可使用以下代碼代替

jf.addWindowListener(new WindowAdapter() {

@Override
     public void windowClosing(WindowEvent e) {
                super.windowClosing(e);
                System.exit(0);
            }
});

import java.awt.Container;

import java.awt.GridLayout;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.ImageIcon;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JPanel;

public class Demo10XOGame extends JFrame{

JPanel jp = new JPanel();

public Demo10XOGame() {

 Container c = this.getContentPane();

 c.add(jp);

 jp.setLayout(new GridLayout(3, 3));

 for (int i = 0; i < 9; i++) {

 XOButton jb = new XOButton();

 jp.add(jb);

 }

 this.setSize(500, 500);

 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

 this.setLocationRelativeTo(null);

 this.setVisible(true);

}

public static void main(String[] args) {

 new Demo10XOGame();

}

}

private ImageIcon X, O;

byte value = 0;

public XOButton() {

 X = new ImageIcon(this.getClass().getResource("x.png"));

 O = new ImageIcon(this.getClass().getResource("o.png"));

 this.addActionListener(this);

}

@Override

public void actionPerformed(ActionEvent e) {

 value++;

 value %= 3;

 switch (value) {

 case 0:

 setIcon(null);

 break;

 case 1:

 setIcon(X);

 break;

 case 2:

 setIcon(O);

 }

}

}