JAVA高手来帮帮我

import javax.swing.SwingUtilities;
import javax.swing.JPanel;
import javax.swing.JFrame;
import javax.swing.JTextField;
import java.awt.Rectangle;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import javax.swing.JButton;

public class GetSum extends JFrame {

private static final long serialVersionUID = 1L;

private JPanel jContentPane = null;

private JTextField first = null;

private JLabel plus = null;

private JTextField second = null;

private JButton getBt = null;

private JTextField sum = null;

private JButton clearBt = null;

private JTextField getFirst() {
if (first == null) {
first = new JTextField();
first.setText("0");
first.setBounds(new Rectangle(5, 19, 80, 22));
}
return first;
}

private JTextField getSecond() {
if (second == null) {