修改后的代码如下：

import java.awt.Color; import java.awt.Container; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JButton; import javax.swing.JTextField; import javax.swing.ButtonGroup; import javax.swing.JOptionPane; import javax.swing.JRadioButton;

public class Test1 extends JFrame implements ActionListener {

private static final long serialVersionUID = 920921981358099067L;
private JLabel lbPer, lbCom, lbLast;
private JButton btnStart, btnOne, btnTwo, btnThree;
private JTextField tfPcshow, tfLastshow;
private boolean win = true;
public Test1() {
    super("拿火柴小游戏");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(600, 300);
    setResizable(false);
    initUI();
    setLocationRelativeTo(null);
}
private void initUI() {
    Container container = getContentPane();
    ButtonGroup group = new ButtonGroup();
    btnStart = new JButton("开始新游戏");
    btnStart.setBounds(410, 50, 150, 30);
    lbPer = new JLabel("人拿火柴数");
    lbPer.setBounds(40, 50, 120, 30);
    lbCom = new JLabel("计算机拿火柴数");
    lbCom.setBounds(40, 100, 120, 30); 
    lbLast = new JLabel("剩余火柴数");
    lbLast.setBounds(40, 150, 120, 30);
    btnOne = new JButton("1");
    btnOne.setBounds(210, 50, 80, 40);
    btnTwo = new JButton("2");
    btnTwo.setBounds(310, 50, 80, 40);
    btnThree = new JButton("3");
    btnThree.setBounds(410, 100, 80, 40);
    tfPcshow = new JTextField();
    tfPcshow.setBounds(210, 100, 150, 30);
    tfLastshow = new JTextField();
    tfLastshow.setBounds(210, 150, 150, 30);
    btnStart.addActionListener(this);
    btnOne.addActionListener(this);
    btnTwo.addActionListener(this);
    btnThree.addActionListener(this);
    group.add(btnOne);
    group.add(btnTwo);
    group.add(btnThree);
    container.setLayout(null);
    container.add(lbPer);
    container.add(lbCom);
    container.add(lbLast);
    container.add(btnStart);
    container.add(btnOne);
    container.add(btnTwo);
    container.add(btnThree);
    container.add(tfPcshow);
    container.add(tfLastshow);
}
public void actionPerformed(ActionEvent e) {
	if (e.getSource() == btnStart) {
        int mode = JOptionPane.showOptionDialog(this,
        		"请选择游戏难度",
                "游戏难度选择",
                JOptionPane.YES_NO_OPTION,
                JOptionPane.QUESTION_MESSAGE,
                null,
                new String[]{"简单", "普通"},
                "简单");
        if(mode == JOptionPane.YES_OPTION){
            startNewGame(10); // 简单模式，初始火柴数为10
        }else{
            startNewGame(20); // 普通模式，初始火柴数为20
        }
        return;
	}
	int k = Integer.parseInt(((JButton)e.getSource()).getText());
	int pc = computer(k); // 计算机拿的火柴数
	if(sumMatch <= pc+k){ // 火柴数不够拿
		JOptionPane.showMessageDialog(this, "火柴数不足，请重新选择", "错误", JOptionPane.ERROR_MESSAGE);
		return;
	}
	sumMatch -= (pc + k);
    if (sumMatch == 0) {
        JOptionPane.showMessageDialog(this, "恭喜你赢了！", "游戏结束", JOptionPane.INFORMATION_MESSAGE);
        startNewGame(sumMatch); // 胜利后开始新游戏
    } else if (sumMatch < 0) {
        JOptionPane.showMessageDialog(this, "请开始新游戏", "游戏结束", JOptionPane.INFORMATION_MESSAGE);
        startNewGame(sumMatch); // 失败后开始新游戏
    }
    tfPcshow.setText("计算机拿了" + pc + "根");
    tfLastshow.setText("火柴剩余" + sumMatch + "根");
    if (!win) {
        JOptionPane.showMessageDialog(this, "你输了，再试一次吧", "游戏结束", JOptionPane.INFORMATION_MESSAGE);
        startNewGame(sumMatch); // 输了后开始新游戏
    }
}
private void startNewGame(int matchCount){
	sumMatch = matchCount;
	tfPcshow.setText("");
	tfLastshow.setText("");
}
private int computer(int k) {
	int ret = 0;
	if(k == 1){ // 如果人拿一根，则计算机随机拿1-3根
		ret = (int) (Math.random() * (3 - 1)) + 1;
    }else{ // 如果人拿两或三根，则计算机自动选择拿剩余的火柴数的一半
    	ret = (sumMatch - k) / 2;
    }
	if(ret < 1){ // 计算机至少拿一根火柴
		ret = 1;
	}else if(ret > 3){ // 计算机最多只能拿三根火柴
		ret = 3;
	}
	return ret;
}
public static void main(String[] args) {
    Test1 frame = new Test1();
    frame.setVisible(true);
}

}