java如何弹出文本框 java 点击按钮后弹出文本框

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Test extends JFrame implements ActionListener{
JPanel panel   =new JPanel();
JButton b1     =new JButton("1");
JButton b2     =new JButton("2");
JButton b3     =new JButton(".");
JLabel  lbl    =new JLabel("我是标签");
JTextField txt =new JTextField("",10);
public Test(){
this.setLayout(new FlowLayout());
panel.add(b1);panel.add(b2);panel.add(b3);panel.add(lbl);panel.add(txt);
this.add(panel);
b1.addActionListener(this);
b2.addActionListener(this);
b3.addActionListener(this);
}
public static void main(String[] args) {
Test test=new Test();
test.setSize(400,260);
test.setLocationRelativeTo(null);
test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
test.setVisible(true);
}
@Override
public void actionPerformed(ActionEvent ae) {
txt.setText( txt.getText() + ae.getActionCommand() );
}
}