JPanel类未添加到JFrame

Question

我无法从主类获取JFrame来显示另一类的JPanel。 一切都能正确编译这是我的扩展JFrame的主类代码：

public OnlineCarSalesSystem(){
    setTitle("Online Car Sales System");
    setVisible(true);
    setExtendedState(JFrame.MAXIMIZED_BOTH);
    setLayout(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    add(new Login());
}

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

在上面的代码中，我添加了add(new Login()); 但它没有在我的JFrame上显示该面板。 在下面的代码中，我使用JPanel扩展了我的课程。 这是JPanel类代码：

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class Login extends JPanel{
    JLabel loginLabel = new JLabel("Login ID");
    JLabel passwordLabel = new JLabel("Password");
    JTextField loginTextField = new JTextField();
    JPasswordField passwordTextField = new JPasswordField();
    JButton submitButton = new JButton("Submit");
    JButton registration = new JButton("new Registration");
    JLabel noaccountLabel = new JLabel("No Account yet!!!");
    public void Login(){
        setBounds(0,0,500,500);
        setBackground(Color.red);
        setVisible(true);
        loginLabel.setBackground(Color.cyan);
        passwordLabel.setBackground(Color.cyan);
        loginTextField.setBounds(680, 103,90,20);
        add(loginTextField);
        loginLabel.setBounds(600, 100,90,30);
        add(loginLabel); 
        passwordTextField.setBounds(680, 153,90,20);
        passwordTextField.setEchoChar('*');
        add(passwordTextField);
        passwordLabel.setBounds(600, 150,90,30);
        add(passwordLabel); 
        add(submitButton);
        submitButton.setBounds(640,200,90,30);
        submitButton.addActionListener(new ActionListener() {   //////Submit Button
            public void actionPerformed(ActionEvent e) {

            }
        });
        add(registration);
        registration.setBounds(638,270,96,30);
        add(noaccountLabel);
        noaccountLabel.setBackground(Color.cyan);
        noaccountLabel.setBounds(640,250,90,30);
        registration.addActionListener(new ActionListener() {   //////registration Button
            public void actionPerformed(ActionEvent e) {

            }
        });
    }
}

Answer 1

问题在于代码中的任何时候都不会执行Login()函数。 您可能要更改

public void Login() { ... }

至

public Login() { ... }

因此代码在对象初始化时执行