用java代码写一个登录

以下是 Java 代码实现一个简单的登录界面：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Login extends JFrame implements ActionListener {
    private JLabel userLabel, passwordLabel;
    private JTextField userText;
    private JPasswordField passwordText;
    private JButton loginButton, cancelButton;

    public Login() {
        setTitle("登录");
        setSize(300, 150);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setResizable(false);

        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints constraints = new GridBagConstraints();
        constraints.anchor = GridBagConstraints.WEST;
        constraints.insets = new Insets(10, 10, 10, 10);

        userLabel = new JLabel("用户名：");
        constraints.gridx = 0;
        constraints.gridy = 0;
        panel.add(userLabel, constraints);

        userText = new JTextField(20);
        constraints.gridx = 1;
        panel.add(userText, constraints);

        passwordLabel = new JLabel("密码：");
        constraints.gridx = 0;
        constraints.gridy = 1;
        panel.add(passwordLabel, constraints);

        passwordText = new JPasswordField(20);
        constraints.gridx = 1;
        panel.add(passwordText, constraints);

        loginButton = new JButton("登录");
        loginButton.addActionListener(this);
        constraints.gridx = 0;
        constraints.gridy = 2;
        constraints.gridwidth = 2;
        constraints.anchor = GridBagConstraints.CENTER;
        panel.add(loginButton, constraints);

        cancelButton = new JButton("取消");
        cancelButton.addActionListener(this);
        constraints.gridx = 0;
        constraints.gridy = 3;
        constraints.gridwidth = 2;
        constraints.anchor = GridBagConstraints.CENTER;
        panel.add(cancelButton, constraints);

        add(panel);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == loginButton) {
            String user = userText.getText();
            String password = new String(passwordText.getPassword());
            if (user.equals("admin") && password.equals("admin123")) {
                JOptionPane.showMessageDialog(this, "登录成功！");
            } else {
                JOptionPane.showMessageDialog(this, "用户名或密码错误！", "错误", JOptionPane.ERROR_MESSAGE);
            }
        } else if (e.getSource() == cancelButton) {
            System.exit(0);
        }
    }

    public static void main(String[] args) {
        new Login();
    }
}

这段代码实现了一个简单的登录界面，包括用户名、密码输入框和登录、取消按钮。当用户点击登录按钮时，程序会获取输入的用户名和密码，如果用户名和密码都是“admin”，则弹出“登录成功”的提示框；否则弹出“用户名或密码错误”的错误提示框。当用户点击取消按钮时，程序会退出。