java 这段代码为什么运行不了

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class knappEx2 extends JFrame {
JButton b1=new JButton("Show");
JButton b2=new JButton("Hide");
JTextField txt=new JTextField(10);
JFrame win2=new JFrame();
ActionListener buttonListener=new ActionListener(){
public void actionPerformed(ActionEvent e){
if(((JButton)e.getSource()).getText().equals("Show")){
win2.setVisible(true);
txt.setText("Showing window 2");
}
else{
win2.setVisible(false);
txt.setText("Hiding window 2");
}
}

public knappEx2(){
b1.addActionListener(buttonListener);
b2.addActionListener(buttonListener);
Container cp=getContentPane();
cp.setLayout(new FlowLayout());
cp.add(b1);
cp.add(b2);
cp.add(txt);
pack();
setVisible(true);
setTitle("knapptest");
wi

是你代码有错误！
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class knappEx2 extends JFrame {
JButton b1 = new JButton("Show");

JButton b2 = new JButton("Hide");

JTextField txt = new JTextField(10);

JFrame win2 = new JFrame();

ActionListener buttonListener = new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (((JButton) e.getSource()).getText().equals("Show")) {
win2.setVisible(true);
txt.setText("Showing window 2");
} else {
win2.setVisible(false);
txt.setText("Hiding window 2");
}
}
};// 你这里分号都给丢了！

public knappEx2() {
b1.addActionListener(buttonListener);
b2.addActionListener(buttonListener);
Container cp = getContentPane();
cp.setLayout(new FlowLayout());
cp.add(b1);
cp.add(b2);