Erro em labels

import java.awt.BorderLayout;

import java.awt.EventQueue;

import java.awt.Font;

import java.awt.GridBagConstraints;

import java.awt.GridBagLayout;

import java.awt.Insets;

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.JOptionPane;

import javax.swing.JPanel;

import javax.swing.JTextField;

import javax.swing.border.EmptyBorder;

private JPanel contentPane;
private JTextField txtDividendo;
private JTextField txtDivisor;

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

/**
 * Create the frame.
 */
public Modulo() {
	setTitle("M\u00F3dulo");
	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	setBounds(100, 100, 434, 216);
	contentPane = new JPanel();
	contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
	contentPane.setLayout(new BorderLayout(0, 0));
	setContentPane(contentPane);

	JPanel panel = new JPanel();
	contentPane.add(panel, BorderLayout.CENTER);
	GridBagLayout gbl_panel = new GridBagLayout();
	gbl_panel.columnWidths = new int[] { 100, 100, 0, 150 };
	gbl_panel.rowHeights = new int[] { 28, 28, 28, 28, 0, 0, 30 };
	gbl_panel.columnWeights = new double[] { 0.0, 0.0, 0.0,
			Double.MIN_VALUE };
	gbl_panel.rowWeights = new double[] { 0.0, 0.0, 0.0, 0.0, 0.0,
			Double.MIN_VALUE };
	panel.setLayout(gbl_panel);

	JLabel lblNewLabel = new JLabel("Dividendo");
	lblNewLabel.setFont(new Font("Tahoma", Font.BOLD, 14));
	GridBagConstraints gbc_lblNewLabel = new GridBagConstraints();
	gbc_lblNewLabel.fill = GridBagConstraints.BOTH;
	gbc_lblNewLabel.insets = new Insets(0, 0, 5, 5);
	gbc_lblNewLabel.gridx = 0;
	gbc_lblNewLabel.gridy = 0;
	panel.add(lblNewLabel, gbc_lblNewLabel);

	txtDividendo = new JTextField();
	GridBagConstraints gbc_txtDividendo = new GridBagConstraints();
	gbc_txtDividendo.fill = GridBagConstraints.BOTH;
	gbc_txtDividendo.insets = new Insets(0, 0, 5, 5);
	gbc_txtDividendo.gridx = 1;
	gbc_txtDividendo.gridy = 0;
	panel.add(txtDividendo, gbc_txtDividendo);
	txtDividendo.setColumns(10);

	JLabel lblDivisor = new JLabel("Divisor");
	lblDivisor.setFont(new Font("Tahoma", Font.BOLD, 14));
	GridBagConstraints gbc_lblDivisor = new GridBagConstraints();
	gbc_lblDivisor.fill = GridBagConstraints.BOTH;
	gbc_lblDivisor.insets = new Insets(0, 0, 5, 5);
	gbc_lblDivisor.gridx = 0;
	gbc_lblDivisor.gridy = 1;
	panel.add(lblDivisor, gbc_lblDivisor);

	txtDivisor = new JTextField();
	GridBagConstraints gbc_txtDivisor = new GridBagConstraints();
	gbc_txtDivisor.fill = GridBagConstraints.BOTH;
	gbc_txtDivisor.insets = new Insets(0, 0, 5, 5);
	gbc_txtDivisor.gridx = 1;
	gbc_txtDivisor.gridy = 1;
	panel.add(txtDivisor, gbc_txtDivisor);
	txtDivisor.setColumns(10);

	JLabel lblResultado = new JLabel("Resultado:");
	lblResultado.setFont(new Font("Tahoma", Font.BOLD, 14));
	GridBagConstraints gbc_lblResultado = new GridBagConstraints();
	gbc_lblResultado.gridwidth = 4;
	gbc_lblResultado.fill = GridBagConstraints.BOTH;
	gbc_lblResultado.insets = new Insets(0, 0, 5, 0);
	gbc_lblResultado.gridx = 0;
	gbc_lblResultado.gridy = 2;
	panel.add(lblResultado, gbc_lblResultado);

	JLabel lblExplicao = new JLabel("Explica\u00E7\u00E3o:");
	lblExplicao.setFont(new Font("Tahoma", Font.BOLD, 14));
	GridBagConstraints gbc_lblExplicao = new GridBagConstraints();
	gbc_lblExplicao.gridwidth = 4;
	gbc_lblExplicao.insets = new Insets(0, 0, 5, 0);
	gbc_lblExplicao.fill = GridBagConstraints.BOTH;
	gbc_lblExplicao.gridx = 0;
	gbc_lblExplicao.gridy = 3;
	panel.add(lblExplicao, gbc_lblExplicao);

	JButton btnCalcular = new JButton("Calcular");
	btnCalcular.addActionListener(new ActionListener() {
		public void actionPerformed(ActionEvent arg0) {

			try {
				int dividendo = Integer.parseInt(txtDividendo.getText());
				int divisor = Integer.parseInt(txtDivisor.getText());

				int res;
				int i = 1;

				if (divisor == 0) {
					JOptionPane
							.showMessageDialog(null,
									"Digite um valor diferente de zero para o divisor.");
				} else {

					while (divisor * i <= dividendo) {

						i += 1;

					}

					i -= 1;
					res = (dividendo % divisor);

					lblResultado.setText("O módulo entre " + dividendo
							+ " e " + divisor + " é: " + res + ".");

					lblExplicacao.setText("Porque " + dividendo
							+ " dividido por " + divisor + " é igual a "
							+ i + " e sobra " + res + ".");
				}
			}

			catch (Exception ex)

			{
				JOptionPane.showMessageDialog(null, "Erro!");

			}

		}

	});
	GridBagConstraints gbc_btnCalcular = new GridBagConstraints();
	gbc_btnCalcular.insets = new Insets(0, 0, 5, 0);
	gbc_btnCalcular.gridx = 2;
	gbc_btnCalcular.gridy = 4;
	panel.add(btnCalcular, gbc_btnCalcular);
	btnCalcular.setFont(new Font("Tahoma", Font.BOLD, 14));
}