Thread: Error Objects Swing

hello I have a problem with a JFrame I can not access objects JButtom to use their attributes, will not let me enable or disable the objects I have declared as public and not anything I can use only within the class constructor

Este es el error que me sale

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at logica.frmRegistro.onVariables(frmRegistro.java:20 8)
at logica.frmRegistro.access$0(frmRegistro.java:199)
at logica.frmRegistro$2.actionPerformed(frmRegistro.j ava:139)
at javax.swing.AbstractButton.fireActionPerformed(Abs tractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed (AbstractButton.java:2318)

package logica;
 
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
 
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTable;
import javax.swing.border.EmptyBorder;
import javax.swing.JTextField;
 
import datos.connDb;
import javax.swing.border.TitledBorder;
import javax.swing.border.LineBorder;
import java.awt.Color;
import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JLabel;
import javax.swing.LayoutStyle.ComponentPlacement;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
 
public class frmRegistro extends JFrame {
 
	private JPanel contentPane;
 
	connDb objDb;
	private JTextField txtId;
	private JTextField txtNombres;
	private JTextField txtDni;
	private JTextField txtDireccion;
	private JTextField txtCargo;
	private JTextField txtTelefono;
 
	private JButton btnNuevo;
	private JButton btnInsertar;
	private JButton btnBuscar;
	private JButton btnActualizar;
	private JTable table;
 
 
	/**
	 * Launch the application.
	 */
 
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					frmRegistro frame = new frmRegistro();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}
 
	/**
	 * Create the frame.
	 */
	public frmRegistro() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 732, 411);
		setFont(new Font("Droid Sans", Font.BOLD, 11));
		setTitle("Registro de Usuarios");
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		setContentPane(contentPane);
 
		JPanel panel = new JPanel();
		panel.setBorder(new TitledBorder(new LineBorder(new Color(99, 130, 191)), "Registro de datos", TitledBorder.LEADING, TitledBorder.TOP, null, new Color(128, 0, 0)));
		panel.setLayout(null);
		panel.setBounds(12, 12, 706, 141);
 
		txtId = new JTextField();
		txtId.setBounds(126, 39, 114, 19);
		txtId.setFont(new Font("Droid Sans", Font.PLAIN, 11));
		panel.add(txtId);
		txtId.setColumns(10);
 
		table = new JTable();
		GroupLayout gl_contentPane = new GroupLayout(contentPane);
		gl_contentPane.setHorizontalGroup(
			gl_contentPane.createParallelGroup(Alignment.LEADING)
				.addGroup(gl_contentPane.createSequentialGroup()
					.addGap(7)
					.addComponent(panel, GroupLayout.PREFERRED_SIZE, 706, GroupLayout.PREFERRED_SIZE)
					.addContainerGap(GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
				.addGroup(Alignment.TRAILING, gl_contentPane.createSequentialGroup()
					.addContainerGap(GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
					.addComponent(table, GroupLayout.PREFERRED_SIZE, 701, GroupLayout.PREFERRED_SIZE)
					.addContainerGap())
		);
		gl_contentPane.setVerticalGroup(
			gl_contentPane.createParallelGroup(Alignment.TRAILING)
				.addGroup(gl_contentPane.createSequentialGroup()
					.addComponent(panel, GroupLayout.PREFERRED_SIZE, 148, GroupLayout.PREFERRED_SIZE)
					.addPreferredGap(ComponentPlacement.UNRELATED)
					.addComponent(table, GroupLayout.PREFERRED_SIZE, 205, GroupLayout.PREFERRED_SIZE)
					.addContainerGap())
		);
 
		txtNombres = new JTextField();
		txtNombres.setFont(new Font("Droid Sans", Font.PLAIN, 11));
		txtNombres.setBounds(453, 39, 240, 19);
		panel.add(txtNombres);
		txtNombres.setColumns(10);
 
		txtDni = new JTextField();
		txtDni.setFont(new Font("Droid Sans", Font.PLAIN, 11));
		txtDni.setBounds(126, 59, 114, 19);
		panel.add(txtDni);
		txtDni.setColumns(10);
 
		txtDireccion = new JTextField();
		txtDireccion.setFont(new Font("Droid Sans", Font.PLAIN, 11));
		txtDireccion.setBounds(126, 79, 230, 19);
		panel.add(txtDireccion);
		txtDireccion.setColumns(10);
 
		txtCargo = new JTextField();
		txtCargo.setFont(new Font("Droid Sans", Font.PLAIN, 11));
		txtCargo.setBounds(453, 59, 114, 19);
		panel.add(txtCargo);
		txtCargo.setColumns(10);
 
		txtTelefono = new JTextField();
		txtTelefono.setFont(new Font("Droid Sans", Font.PLAIN, 11));
		txtTelefono.setBounds(453, 79, 114, 19);
		panel.add(txtTelefono);
		txtTelefono.setColumns(10);
 
		JButton btnNuevo = new JButton("Nuevo");
		btnNuevo.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				onVariables();
			}
		});
		btnNuevo.setBounds(100, 110, 117, 25);
		panel.add(btnNuevo);
		contentPane.setLayout(gl_contentPane);
 
		JButton btnInsertar = new JButton("Insertar");
		btnInsertar.setBounds(239, 110, 117, 25);
		panel.add(btnInsertar);
 
		JButton btnBuscar = new JButton("Buscar");
		btnBuscar.setBounds(378, 110, 117, 25);
		panel.add(btnBuscar);
 
		JButton btnActualizar = new JButton("Actualizar");
		btnActualizar.setBounds(517, 110, 117, 25);
		panel.add(btnActualizar);
 
		JLabel lblNewLabel = new JLabel("Id Usuario :");
		lblNewLabel.setBounds(48, 39, 74, 19);
		lblNewLabel.setFont(new Font("Droid Sans", Font.BOLD, 11));
		panel.add(lblNewLabel);
		contentPane.setLayout(gl_contentPane);
 
		JLabel lblNewLabel_1 = new JLabel("Nombres y Apellidos :");
		lblNewLabel_1.setFont(new Font("Droid Sans", Font.BOLD, 11));
		lblNewLabel_1.setBounds(321, 39, 127, 19);
		panel.add(lblNewLabel_1);
		contentPane.setLayout(gl_contentPane);
 
		JLabel lblNewLabel_2 = new JLabel("Doc. Identidad :");
		lblNewLabel_2.setFont(new Font("Droid Sans", Font.BOLD, 11));
		lblNewLabel_2.setBounds(24, 59, 97, 19);
		panel.add(lblNewLabel_2);
		contentPane.setLayout(gl_contentPane);
 
		JLabel lblNewLabel_3 = new JLabel("Dirección :");
		lblNewLabel_3.setFont(new Font("Droid Sans", Font.BOLD, 11));
		lblNewLabel_3.setBounds(52, 79, 70, 19);
		panel.add(lblNewLabel_3);
		contentPane.setLayout(gl_contentPane);
 
		JLabel lblNewLabel_4 = new JLabel("Cargo :");
		lblNewLabel_4.setFont(new Font("Droid Sans", Font.BOLD, 11));
		lblNewLabel_4.setBounds(399, 59, 48, 19);
		panel.add(lblNewLabel_4);
		contentPane.setLayout(gl_contentPane);
 
		JLabel lblNewLabel_5 = new JLabel("Telefono :");
		lblNewLabel_5.setFont(new Font("Droid Sans", Font.BOLD, 11));
		lblNewLabel_5.setBounds(383, 79, 63, 19);
		panel.add(lblNewLabel_5);
		contentPane.setLayout(gl_contentPane);	
		offVariables();
		btnInsertar.setEnabled(false);
		btnBuscar.setEnabled(false);
		btnActualizar.setEnabled(false);
	}
 
	private void onVariables()
	{
		txtId.setEnabled(true);
		txtNombres.setEnabled(true);
		txtDni.setEnabled(true);
		txtCargo.setEnabled(true);
		txtDireccion.setEnabled(true);
		txtTelefono.setEnabled(true);
 
		btnNuevo.setEnabled(true);
		btnActualizar.setEnabled(true);
		btnBuscar.setEnabled(true);
 
	}
 
	private void offVariables()
	{
		txtId.setEnabled(false);
		txtNombres.setEnabled(false);
		txtDni.setEnabled(false);
		txtCargo.setEnabled(false);
		txtDireccion.setEnabled(false);
		txtTelefono.setEnabled(false);
		//btnInsertar.setEnabled(false);
		//btnBuscar.setEnabled(false);
		//btnActualizar.setEnabled(false);
	}
}