App.java

import javax.swing.SwingUtilities;

public class App {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            LoginForm loginForm = new LoginForm();
            loginForm.setVisible(true);
        });
    }
}

LoginForm.java

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

public class LoginForm extends JFrame {
    private JTextField textFieldUsername;
    private JPasswordField passwordFieldPassword;
    private JButton buttonLogin;
    private JButton buttonExit;

    public LoginForm() {
        setTitle("TEPOO - Login");
        setSize(300, 160);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        textFieldUsername = new JTextField();
        passwordFieldPassword = new JPasswordField();

        buttonLogin = new JButton("Login");
        buttonExit = new JButton("Sair");

        JPanel innerPanel = new JPanel(new GridLayout(3, 1));
        innerPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

        innerPanel.add(new JLabel("Usuário:"));
        innerPanel.add(textFieldUsername);
        innerPanel.add(new JLabel("Senha:"));
        innerPanel.add(passwordFieldPassword);
        innerPanel.add(buttonLogin);
        innerPanel.add(buttonExit);

        JLabel labelTitle = new JLabel("Entrar:");
        labelTitle.setAlignmentX(JLabel.CENTER_ALIGNMENT);

        JPanel outterPanel = new JPanel();
        outterPanel.setLayout(new BoxLayout(outterPanel, BoxLayout.Y_AXIS));
        outterPanel.setBorder(BorderFactory.createEmptyBorder(10, 0, 10, 0));

        outterPanel.add(labelTitle);
        outterPanel.add(innerPanel);

        this.add(outterPanel);

        buttonLogin.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String username = textFieldUsername.getText();
                String password = String.valueOf(passwordFieldPassword.getPassword());

                if (username.equals("Admin") && password.equals("1234")) {
                    JOptionPane.showMessageDialog(null, "Bem-vindo, Admin!", null, JOptionPane.INFORMATION_MESSAGE);
                } else {
                    JOptionPane.showMessageDialog(null, "Usuário e/ou senha inválidos.", "Erro",
                            JOptionPane.ERROR_MESSAGE);
                }
            }
        });

        buttonExit.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.exit(0);
            }
        });
    }
}