[JAVA ] IntelliJ GUI폼 작성시

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

public class MainFrame extends JFrame {
    private JPanel panelRoot;
    private JTextField txtUserId;
    private JPasswordField txtUserPw;
    private JButton btnSignUp;
    private JButton btnLogIn;
    
    public MainFrame() {
        setSize(800, 600);
        add(panelRoot);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
        btnSignUp.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if (txtUserId.getText().isEmpty()) {
                    JOptionPane.showMessageDialog(MainFrame.this, "Please fill in User id");
                }
                else {
                
                }
            }
        });
        btnLogIn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
            }
        });
    }
    
    private void createUIComponents() {
        // TODO: place custom component creation code here
    }
    public static void main(String[] args) {
        new MainFrame();
    }
}

 

showMessageDialog(MainFrame.this, "selected Sign Up") <<<< 그냥 this 아님 주의

메인프레임을 다른 곳으로 옮겨서 클릭해도

팝업창은 메인프레임 따라서 팝업됨(메인프레임 기준)