然后书里接着说啥上溯，下溯。。用面向对象的方法重写。。。
我就按着我的理解重写了下。。。
package QQ;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class QQLogin extends JFrame implements ActionListener {
JTextField txtUser = new JTextField();
JPasswordField txtPass = new JPasswordField();
@Override
public Container getContentPane() {
//new assembly
JLabel labUser = new JLabel("用户名");
JLabel labPass = new JLabel("密码");
//JTextField txtUser = new JTextField();
//JPasswordField txtPass = new JPasswordField();
JButton btnLogin = new JButton("登录");
JButton btnReg = new JButton("注册");
JButton btnCancel = new JButton("取消");
btnLogin.addActionListener(this);
btnReg.addActionListener(this);
btnCancel.addActionListener(this);
JPanel main = new JPanel();
//input
JPanel panInput = new JPanel();
panInput.setLayout(new GridLayout(2,2));
panInput.add(labUser);
panInput.add(txtUser);
panInput.add(labPass);
panInput.add(txtPass);
//button
JPanel panButton = new JPanel();
panButton.setLayout(new FlowLayout());
panButton.add(btnLogin);
panButton.add(btnReg);
panButton.add(btnCancel);
//windows
this.setSize(250,125);
this.setLayout(new BorderLayout());
main.add(panInput,BorderLayout.CENTER);
main.add(panButton, BorderLayout.SOUTH);
return main;
}
public static void main(String args[]) {
QQLogin w = new QQLogin();
w.setVisible(true);
}
@Override
public void actionPerformed(ActionEvent arg0) {
if(arg0.getActionCommand().equals("登录")) {
System.out.println("用户点了登录");
}
if(arg0.getActionCommand().equals("注册")) {
System.out.println("用户点了注册");
}
if(arg0.getActionCommand().equals("取消")) {
System.out.println("用户点了取消");
}
}
}

然后发现，改了后虽然没报错，但是弹出框长宽都变成0了，但我自己又不知道哪里写错了。。。求大神指点，自学不易啊

顶起来