import javax.swing.*;
import java.awt.event.*;
public class close
{
 public static void main(String [] args)
 {
  new closed();
 }
}
class closed extends JFrame
{
 Object obj[] = {"OK","Cancel"};
 public closed()
 {
  setSize(300,200);
  setVisible(true);
  addWindowListener(new WindowAdapter()
  {
   public void windowClosing(WindowEvent w)
   {
    int i = JOptionPane.showOptionDialog(null,"Exit OK?","Exit",JOptionPane.OK_CANCEL_OPTION,JOptionPane.QUESTION_MESSAGE,null,obj,obj[0]);
    if(i == 0)
     System.exit(0);
   }
  });
 }
}

功能很简单，就是点大差而弹出对话框来询问是否关闭程序，但要写什么代码才能让点取消返回程序界面，现在点了就什么反应都没了……