public static Connection conectabd() throws ClassNotFoundException {

    try {
        Class.forName("org.postgresql.Driver");
         Connection con = DriverManager.getConnection("jdbc:postgresql://localhost:5432/crud","postgres","tmk9405");
        JOptionPane.showMessageDialog(null,"Conectado com sucesso!");
        return con;
    }

    catch (SQLException error) {

        JOptionPane.showMessageDialog(null, error);
        return null;
    }
}

/**
 *
 */
private static final long serialVersionUID = 1L;
private JPanel contentPane;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                frmLogin frame = new frmLogin();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */

Connection con = null;
PreparedStatement pst = null;
ResultSet rs = null;
private JTextField txtUsuario;
private JPasswordField txtSenha;
private JLabel lblLogin;
private JLabel lblSistemaDesenvolvidoPela;

public frmLogin() throws ClassNotFoundException {
    setIconImage(Toolkit.getDefaultToolkit().getImage("C:\Users\Alessandro\Downloads\icons8-senha-50.png"));
    setTitle("Login de usuu00E1rio");


    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 640, 299);
    contentPane = new JPanel();
    contentPane.setBorder(new TitledBorder(null, "", TitledBorder.CENTER, TitledBorder.TOP, null, null));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    JLabel lblUsurio = new JLabel("Usuu00E1rio:");
    lblUsurio.setBounds(139, 70, 85, 20);
    lblUsurio.setHorizontalAlignment(SwingConstants.CENTER);
    lblUsurio.setFont(new Font("Arial", Font.BOLD, 12));
    contentPane.add(lblUsurio);

    txtUsuario = new JTextField();
    txtUsuario.setBounds(224, 73, 179, 20);
    txtUsuario.setColumns(10);
    contentPane.add(txtUsuario);

    JLabel lblSenha = new JLabel("senha:");
    lblSenha.setBounds(139, 106, 85, 20);
    lblSenha.setHorizontalAlignment(SwingConstants.CENTER);
    lblSenha.setFont(new Font("Arial", Font.BOLD, 12));
    contentPane.add(lblSenha);

    JButton btnEntrar = new JButton("ENTRAR");
    btnEntrar.setIcon(new ImageIcon("C:\Users\Alessandro\Downloads\icones\Icones\accept.png"));
    btnEntrar.setBounds(262, 166, 104, 23);
    btnEntrar.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            Logar();
        }
    });

    txtSenha = new JPasswordField();
    txtSenha.setBounds(224, 107, 179, 20);
    contentPane.add(txtSenha);
    contentPane.add(btnEntrar);

    lblLogin = new JLabel("LOGIN");
    lblLogin.setFont(new Font("Arial", Font.BOLD, 15));
    lblLogin.setBounds(262, 11, 67, 21);
    contentPane.add(lblLogin);

    lblSistemaDesenvolvidoPela = new JLabel("Sistema desenvolvido por Alesssandro Jacques.)");
    lblSistemaDesenvolvidoPela.setForeground(Color.BLACK);
    lblSistemaDesenvolvidoPela.setFont(new Font("SansSerif", Font.PLAIN, 10));
    lblSistemaDesenvolvidoPela.setBounds(233, 256, 391, 14);
    contentPane.add(lblSistemaDesenvolvidoPela);
    this.setLocationRelativeTo(null); // centralizando formulario
    con = conectaBD.conectabd();

    setResizable(false); //Bloquando a opção maximizar a tela de login
}
    @SuppressWarnings("deprecation")
    public void Logar() {
        String sql = "Select * from login where usuario = ? and senha = ?";
        try {
            pst = con.prepareStatement(sql);
            pst.setString(1, txtUsuario.getText());
            pst.setString(2, txtSenha.getText());

            rs = pst.executeQuery();

            if(rs.next()) {
                frmPrincipal frm = new frmPrincipal();
                frm.setVisible(true);
                dispose();
            }else {
                JOptionPane.showMessageDialog(null,"Usuario e senha inválidos.");
            }
        }
        catch(SQLException error) {
            JOptionPane.showMessageDialog(null, error);
        }
    }

}

private static final long serialVersionUID = 1L;
private JPanel contentPane;
private JTextField txtBusca;
private JButton btnLimpar;
private JButton btnSair;

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {

        public void run() {
            try {
                frmPrincipal frame = new frmPrincipal();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

Connection conectabd=null;

/**
 * Create the frame.
 */
public frmPrincipal() {

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 1124, 744);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    JLabel lblPesquisar = new JLabel("Pesquisar:");
    lblPesquisar.setBounds(50, 52, 85, 33);
    lblPesquisar.setFont(new Font("Tahoma", Font.PLAIN, 18));
    contentPane.add(lblPesquisar);

    txtBusca = new JTextField();
    txtBusca.setBounds(140, 62, 260, 23);
    txtBusca.setColumns(10);
    contentPane.add(txtBusca);
    //pesquisarUsuarios();

    JButton btnBuscar = new JButton("Buscar");
    btnBuscar.setBounds(410, 60, 108, 23);
    btnBuscar.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {

        }
    });
    btnBuscar.setIcon(new ImageIcon("C:\Users\Alessandro\Downloads\icons8-pesquisar-filled-25.png"));
    contentPane.add(btnBuscar);

    btnLimpar = new JButton("Limpar ");
    btnLimpar.setIcon(new ImageIcon("C:\Users\Alessandro\Downloads\icons8-limpar-pesquisa-25.png"));
    btnLimpar.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            txtBusca.setText(null);

        }
    });
    btnLimpar.setBounds(523, 107, 115, 23);
    contentPane.add(btnLimpar);

    btnSair = new JButton("SAIR");
    btnSair.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            System.exit(0);
        }
    });
    btnSair.setBounds(410, 107, 108, 23);
    btnSair.setFont(new Font("Tahoma", Font.BOLD, 11));
    btnSair.setIcon(new ImageIcon("C:\Users\Alessandro\Downloads\icons8-fechar-janela-25.png"));
    contentPane.add(btnSair);

    this.setExtendedState(MAXIMIZED_BOTH); // utiliza para maximizar o formulário
    //setResizable(false); //Bloquando a opção maximizar

    setDefaultCloseOperation(javax.swing.WindowConstants.DO_NOTHING_ON_CLOSE); //tirando a opção fechar o JFRAME

}