最近在做一个实验，不过出现了问题解决不了，求高手帮帮忙，感激不尽啊。。。
题目是：猜数字游戏，程序生成一个0~9随机数，玩家有三次机会猜，三次机会之内猜中了提示猜对了，否则提示正确答案并询问是否继续游戏。
下面是我的代码，我感觉会有挺多问题的，但是不知道怎么改，求高手帮忙。。。。
<%@ page language="java" import="java.util.*" pageEncoding="GBK"%><% String path = request.getContextPath(); String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>GuessNumber</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> </head> <body> <table width="200" height="100" align="center" border="0" bgColor="#0080ff"> <tr> <td> 请猜一个0~9的数字： </td> </tr> <tr> <td> <input type="text" maxlength="1" name="guess"> </td> <td><%=session.getAttribute("answer")%></td> </tr> <tr> <td><%=session.getAttribute("count")%></td> <td> <input type="submit" value="确定" name="ok"> </td> </tr> </table> <% String Guess = new String(request.getParameter("guess").getBytes( "ISO_8859_1"), "GBK"); int n = 3; int num = (int) Math.random() * 10; String count = n + "chances!"; String answer = null; session.setAttribute("count", count); while (n != 0) { if (Guess != null) { int guess = Integer.parseInt(Guess); if (num == guess) { answer = "Congratulation!"; session.setAttribute("answer", answer); break; } else { n--; answer = "Sorry!You are wrong!"; session.setAttribute("answer", answer); count = n + "chances!"; session.setAttribute("count", count); } } else { answer = "Please input a number!"; session.setAttribute("answer", answer); count = n + "chances!"; session.setAttribute("count", count); } } %> </body></html>
54: int n = 3;
55: int num = (int) Math.random() * 10;
56: String count = n + "chances!";
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:524)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:435)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause?
java.lang.NullPointerException
org.apache.jsp.GuessNumber_jsp._jspService(GuessNumber_jsp.java:115)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.13 logs.
[解决办法]
我随便写了个你的例子，不知道满足你的需求么。参考下楼主。
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><% Random r=new Random(); //实例化一个Random类 //随机产生一个大于等于0小于10的整数 int answer=r.nextInt(10); System.out.println("随机产生一个大于等于0小于10的整数："+answer);%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>GuessNumber</title> <script type="text/javascript"> var count=0; var is_correct=false; var answer=<%=answer%>; function check(){ var num=document.getElementById("inputNumber").value; if(num==''){ }else{ if(count<=2&&is_correct==false){ count++; if(num==answer){ alert('恭喜您，猜对了！'); is_correct=true; }else{ alert('不好意思，您猜错了，您还有'+(3-count)+'次机会，请重试！') } } } } </script> </head> <body> <table width="200" height="100" align="center" border="0" bgColor="#0080ff"> <tr> <td> 请猜一个0~9的数字： </td> </tr> <tr> <td> <input type="text" maxlength="1" id="inputNumber"> </td> </tr> <tr> <td> <input type="submit" value="确定" name="checkNumber" onclick="check()"> </td> </tr> </table> </body></html>
[解决办法]
13楼给了一个用JavaScript在页面端进行猜数判断的样例，挺好的。
这里是服务端进行猜数判断的（没做太多差错控制）：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%><%@ page import="java.util.*"%><%response.setHeader("Cache-Control", "no-cache, no-store"); //HTTP 1.1 response.setHeader("Pragma", "no-cache"); //HTTP 1.0 response.setDateHeader("Expires", 0); //prevents caching at the proxy server// 定义变量int MAX = 3;//从提交表单（request）得到用户提交的猜测数String strGuess = request.getParameter("guess");Integer guess = -1;try { guess = Integer.valueOf(strGuess);} catch (Exception ex) {}//从Session得到猜测次数，没有说明是第一次 Integer times = (Integer) session.getAttribute("times");if (times == null || times >= MAX) { times = 0;}if (guess >= 0) { times++;}session.setAttribute("times", times);// 从Session得到随机数，没有则生成Integer num = (Integer) session.getAttribute("num");if (times == 0 || num == null) { num = (int)(Math.random() * 10); session.setAttribute("num",num);}boolean correct = guess.equals(num); // 猜中否？if (correct) session.removeAttribute("times");%><html><body><%if (guess >= 0) { out.write("第"+times+"次，您猜测的数字是：" + guess); if (correct) out.write("，恭喜，正确了！请继续输入以重来。"); else if (times < 3) out.write("，不正确。"); else out.write("，不正确。正确答案是：" + num + "。请继续输入以重来。");}%><p></p> <form method="post"> 请输入猜测数（0～9）： <input type="text" name="guess"> <input type="submit"> </form></body></html>
我的异常网推荐解决方案：An exception occurred processing JSP page,http://www.myexception.cn/j2se/33144.html
我的异常网推荐解决方案：The server encountered an internal error () that prevented it from fulfilling this request.,http://www.myexception.cn/java-web/317.html