哪位大哥帮忙调一下这个程序

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class exam extends JFrame implements ActionListener
{
JButton btnMessage=new JButton("消息");
JButton btnInput=new JButton("输入");
JButton btnConfirm=new JButton("确认");
JButton btnOption=new JButton("选择");
public exam()
{
super("exam");
btnMessage.addActionListener(this);
btnInput.addActionListener(this);
btnConfirm.addActionListener(this);
btnOption.addActionListener(this);
getContentPane().setLayout(new FlowLayout());
getContentPane().add(btnMessage);
getContentPane().add(btnInput);
getContentPane().add(btnConfirm);
getContentPane().add(btnOption);
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);

}
});
}
public static void main(String args[])
{
exam fr=new exam();
fr.pack();
fr.setVisible(true);
}
public void actionPerformed(ActionEvent e)
{
Object[] opt={"确认","取消"};
//JButton instance=(JButton)e.getObject();
Object instance=e.getSource();
if(instance==btnMessage)
JOptionPane.showMessageDialog(this,"消息对话框");
else if(instance==btnInput)
JOptionPane.showInputDialog(this,"输入对话框");
else if(instance==btnConfirm)
JOptionPane.showConfirmDialog(this,"确认对话框");
else
JOptionPane.showOptionDialog(this,"选择对话框","选择",JOptionPane.YES_OPTION,JOptionPane.QUESTION_MESSAGE,null,opt,opt[1]);
}
}

ButtonSelectedActionListener
actionperformed---------P
e.getObject();
JOptionPane,YES_OPTION------逗号
ipt[1]----------opt[1]