课后作业:验证码

import javax.swing.;
import java.awt.;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.util.Random;

public class LoginWithCaptcha extends JFrame {

private JTextField usernameField;  
private JPasswordField passwordField;  
private JTextField captchaField;  
private JLabel captchaLabel;  
private String captchaString;  

public LoginWithCaptcha() {  
    this.setTitle("登录界面");  
    this.setSize(400, 300);  
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    this.setLocationRelativeTo(null);  

    createUI();  
    generateAndSetCaptchaImage();  
}  

private void createUI() {  
    JPanel panel = new JPanel();  
    panel.setLayout(new GridLayout(5, 2));  
    panel.setBackground(new Color(173, 216, 230)); 

    addComponentsToPanel(panel);  
    this.add(panel);  
}  

private void addComponentsToPanel(JPanel panel) {  
    panel.add(new JLabel("账号:"));  
    usernameField = new JTextField();  
    panel.add(usernameField);  

    panel.add(new JLabel("密码:"));  
    passwordField = new JPasswordField();  
    panel.add(passwordField);  

    panel.add(new JLabel("验证码:"));  
    captchaField = new JTextField();  
    panel.add(captchaField);  

    captchaLabel = new JLabel(); 
    panel.add(captchaLabel);  

    JButton refreshButton = createRefreshButton();  
    panel.add(refreshButton);  
}  

private JButton createRefreshButton() {  
    JButton refreshButton = new JButton("刷新");  
    refreshButton.setFont(new Font("Sans Serif", Font.BOLD, 14));   
    refreshButton.setBackground(Color.WHITE);  
    refreshButton.setForeground(Color.BLACK); 

    
    refreshButton.setFocusPainted(false);  
    refreshButton.setBorder(BorderFactory.createEmptyBorder(10, 20, 10, 20)); 

    
    refreshButton.addActionListener(new ActionListener() {  
        public void actionPerformed(ActionEvent e) {  
            generateAndSetCaptchaImage();   
        }  
    });  

    return refreshButton;  
}  

private void generateAndSetCaptchaImage() {  
    captchaString = generateRandomCaptcha();  
    BufferedImage captchaImage = new BufferedImage(200, 100, BufferedImage.TYPE_INT_RGB
    Graphics g = captchaImage.getGraphics();  
    g.setColor(Color.WHITE);  
    g.fillRect(0, 0, 200, 100);  
    g.setColor(Color.BLACK); 
    g.setFont(new Font("Sans Serif", Font.PLAIN, 40));   
    g.drawString(captchaString, 20, 60);  
    g.dispose();  
    captchaLabel.setIcon(new ImageIcon(captchaImage));  
}  

private String generateRandomCaptcha() {  
    
    String chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";   
    Random random = new Random();  
    StringBuilder captcha = new StringBuilder();    
    
    for (int i = 0; i < 4; i++) { 
        int index = random.nextInt(chars.length());  
        captcha.append(chars.charAt(index));  
    }  
    return captcha.toString();  
}  

public static void main(String[] args) {  
    SwingUtilities.invokeLater(() -> new LoginWithCaptcha().setVisible(true));  
}  

}