当前位置: 代码迷 >> Java Web开发 >> NullPointerException该如何解决
  详细解决方案

NullPointerException该如何解决

热度:38   发布时间:2016-04-17 16:26:48.0
NullPointerException该怎么解决
<%@   page   language= "java "   %>
<%@   page   session= "true "   %>
<%@   page   contentType= "text/html;charser=gb2312 "%>
<%@   page   import= "java.lang.* "%>
<%@   page   import= "java.util.* "%>
<%!
public   String   getMessage(int[]   result){
switch(result[0]){
case   -2:return   "san   wei   shu ";
case   -1:return   "ge   shi   wrong! ";
case   0:return   "right ";
default   :return   "go   on! ";
}
}
public   int[]   checkNumber(String   guessnum,String   answernum){
if(guessnum.length()!=3)
return   new   int[]{-2,0,0};
int   num=0;
try{
num=Integer.parseInt(guessnum);
}catch(NumberFormatException   e){
return   new   int[]{-1,0,0};
}
int   a=0;
int   b=0;
for(int   j=0;j <3;j++){
int   pos=answernum.indexOf(guessnum.substring(j,j+1));
if(pos==j)
a++;
else   if(pos> =0)
b++;
}
if(a==3)
return   new   int[]{0,a,b};
else
return   new   int[]{1,a,b};
}
%>
<%
Vector   history=(Vector)session.getValue( "HISTORY ");
String   answernum=(String)session.getValue( "ANSWER ");
String   guessnum=null;
String   message=null;
boolean   gameover=false;
if(history==null||answernum==null){
history=new   Vector();
answernum= "456 ";
session.putValue( "HISTORY ",history);
session.putValue( "ANSWER ",answernum);
}else{
guessnum=request.getParameter( "guess_number ");
int[]   result=checkNumber(guessnum,answernum);
message=getMessage(result)+ "ni   cai   de   shi "+guessnum;
if(result[0]==0)
gameover=true;
else   if(history.size()> =4){
gameover=true;
message+= "answer: "+answernum;
}
history.insertElementAt(message,0);
session.putValue( "ANSWER ",answernum);
}
if(gameover){
session.removeValue( "HISTORY ");
session.removeValue( "ANSWER ");
}
%>
<html>
<title>
a   example   of   session
</title>
<body   bgcolor= "#ffffff ">
<h1> cai   shu   zi! </h1>
<form   name= "form1 "   method= "get "   action= "numguess1.jsp ">
number: <input   type= "text "   name= "guess_number "   size= "4 "   maxlength= "4 ">
<input   type= "submit "   name= "submit "   value= "enter ">
</form>
<%
int   i=history.size();
for(Enumeration   e=history.elements();e.hasMoreElements();){
%>
<%=i%> , <%=(String)e.nextElement()%> <br>
<%
i--;
}
if(gameover){
%>
<form   name= "form2 "   method= "get "   action= "numguess1.jsp ">
<input   type= "submit "   name= "submit "   value= "go   on ">
</form>
<%  
  相关解决方案