JAVA添加按钮监听器

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;

public class ShowButton implements ActionListener{
    private JTextField textField = null;
    private JButton button = null;
    private JFrame frame = null;
   
    public ShowButton(){
        frame = new JFrame("显示按钮文字");
        button = new  JButton("3");
        textField = new JTextField("",20);
        frame.setLayout(new FlowLayout(FlowLayout.LEFT));
        frame.add(textField);
        button.addActionListener(this);
        frame.add(button);
        frame.setSize(400, 100);
        frame.setResizable(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
   
    public void actionPerformed(ActionEvent e) {
        textField.setText("");
        textField.setText(button.getActionCommand());
        System.out.println(button.getActionCommand()+"===");
    }
   
    public static void main(String[] args) {
        new ShowButton();
    }

 

}