java swing 控件问题

Question

代码如下：
 import javax.swing.*;
public class Dialog extends JFrame
{
       public Dialog()
              {                  setTitle("对话框实例");
                  setSize(300,300);
                  String postcode=JOption.showInputDialog(this,"请输入邮政编码","输入提示",JOptionPane.INFORMATION_MESSAGE);
                  JOption.showMessageDialog(this,postcode,"提示",JOptionPane.INFORMATION_MESSAGE);
              }
       public static void main(String[] args)
             {
                  new Dialog().setVisible(true);
             }}
编译时报错如下：
      Dialog.java:9: 找不到符号
符号： 变量 JOption
位置： 类 Dialog
                  String postcode=JOption.showInputDialog(this,"请输入邮政编码","输入提示",JOptionPane.INFORMATION_MESSAGE);
                                  ^
Dialog.java:10: 找不到符号
符号： 变量 JOption
位置： 类 Dialog
                  JOption.showMessageDialog(this,postcode,"提示",JOptionPane.INFORMATION_MESSAGE);
                  ^
2 错误
       我是按书上源码敲下来的，不知到出错在哪里？