用javagui写一个登录页面

下面是一个简单的Java GUI登录页面的示例代码：

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

public class LoginFrame extends JFrame {
    private JLabel usernameLabel, passwordLabel;
    private JTextField usernameField;
    private JPasswordField passwordField;
    private JButton loginButton, cancelButton;

    public LoginFrame() {
        super("Login");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 200);

        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints constraints = new GridBagConstraints();
        constraints.insets = new Insets(5, 5, 5, 5);

        usernameLabel = new JLabel("Username:");
        constraints.gridx = 0;
        constraints.gridy = 0;
        panel.add(usernameLabel, constraints);

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

        usernameField = new JTextField(20);
        constraints.gridx = 1;
        constraints.gridy = 0;
        constraints.fill = GridBagConstraints.HORIZONTAL;
        panel.add(usernameField, constraints);

        passwordField = new JPasswordField(20);
        constraints.gridx = 1;
        constraints.gridy = 1;
        constraints.fill = GridBagConstraints.HORIZONTAL;
        panel.add(passwordField, constraints);

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

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

        getContentPane().add(panel, BorderLayout.CENTER);
        pack();
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) {
        LoginFrame frame = new LoginFrame();
        frame.setVisible(true);
    }
}

这个示例代码创建了一个LoginFrame类，它继承自JFrame类，并包含一个包含用户名和密码文本框以及登录和取消按钮的面板。GridBagLayout布局管理器用于布局面板中的组件，以确保它们在不同大小的屏幕上显示良好。setSize()方法设置窗口大小，setDefaultCloseOperation()方法设置窗口关闭行为，setLocationRelativeTo()方法将窗口放置在屏幕中央。最后，main()方法创建一个LoginFrame实例并显示它。