问如何在点击按钮时将jTextField数据和jLable中的输出相加，然后再次单击textfield值和前一个JLable值？

EN

package stack;

import java.awt.FlowLayout;
import java.awt.Frame;
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.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.JWindow;

public class Gui {



public static void main(String[] args) {
    JFrame frame = new JFrame();
    JLabel jlabel = new JLabel("1");
    JTextField jtext = new JTextField(50);
    JButton but = new JButton("add");
    frame.setBounds(20, 30, 200, 300);
    frame.setLayout(new FlowLayout());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(jlabel);
    frame.add(jtext);
    frame.add(but);
    frame.setVisible(true);
    but.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            String a = jlabel.getText();

            String b = jtext.getText();

            int res = Integer.parseInt(a);
            int res1 = Integer.parseInt(b);
            res = res + res1;
            a = Integer.toString(res);

            jlabel.setText(a);
        }
    });




}

}