第四题

import javax.swing.*; import java.awt.*; public class Login extends JFrame {   // 定义组件   JLabel jl1, jl2;   JTextField jtf;   JPasswordField jpf;   JButton jb;   public Login() {     // 创建组件     jl1 = new JLabel("用户名:");     jl2 = new JLabel("密码:");     jtf = new JTextField(10);     jpf = new JPasswordField(10);     jb = new JButton("登录");     // 设置布局为 GridLayout     this.setLayout(new GridLayout(3, 2));     // 添加组件     this.add(jl1);     this.add(jtf);     this.add(jl2);     this.add(jpf);     this.add(jb);     // 设置窗口属性     this.setTitle("用户登录");     this.setSize(300, 150);     this.setLocationRelativeTo(null);     this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);     this.setVisible(true);     // 为登录按钮添加事件监听器     jb.addActionListener(e -> {       // 获取用户名和密码       String username = jtf.getText();       char[] password = jpf.getPassword();       // 判断用户名和密码是否正确       if ("王恒".equals(username) && "202009280120".equals(new String(password))) {         JOptionPane.showMessageDialog(this, "登录成功！");       } else {         JOptionPane.showMessageDialog(this, "用户名或密码错误！");       }     });   }   public static void main(String[] args) {     new Login();   } }