高分求助:请帮我看看这段代码,为什么老是报错??
-----------以下是查询页面的代码----名称是query_page.htm
<html>
<head>
<meta http-equiv="Content-Language" content="zh-cn">
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta name="GENERATOR" content="Microsoft FrontPage 4.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<title>数据查询</title>
</head>
<body>
<h1 align="center"><font color="#008080">数据查询</font></h1>
<hr>
<form action="query.jsp" method="get" name="query_page">
<table width="679">
<td width="671">
<p align="right"><input type="radio" value="V_code" checked name="R1" tabindex="0">按代码:<input type="text" name="code" value="*" size="20"> </p>
<p align="right"><input type="radio" value="V_name" name="R1" tabindex="1">按名称:<input type="text" name="name" value="*" size="20"> </p>
<p align="right"><input type="radio" value="V_datetime" name="R1" tabindex="2">按日期时间:<input type="text" name="datetime" value="*" size="20">
</p>
</table>
<br>
<p align="center"><input type="submit" value="查询" name="B3">
<input type="submit" value="返回主页" name="B2"></p>
</form>
</body>
</html>
-----以下是显示页面的代码----,名称为:query.jsp
<%@ page language="java" %>
<%@ page import="java.sql.*" %>
<%@ page contentType="text/html; charset=GB2312" %>
<%
String code,name,datetime;
String cond;
String Sql_str;
String driver,url,userID,passwd;
driver="org.gjt.mm.mysql.Driver";
url="jdbc:mysql://localhost:3306/stockdb";
userID="root";
passwd="";
try
{
Class.forName(driver);
}
catch(Exception ex)
{
out.println("load"+driver+"error");
ex.printStackTrace();
}
try
{
cond=request.getParameter("R1");
cond=cond.trim();
out.println("cond="+cond+"<br>");
if (cond=="V_code" )
{
out.println("按代码查询:<br>");
code = request.getParameter("code");
if ( code == "*" )
Sql_str="SELECT * FROM stocklive";
else
Sql_str="SELECT * FROM stocklive WHERE code='"+code+"'";
}
else if ( cond=="V_name" )
{
out.println("按名称查询:<br>");
name = request.getParameter("name");
if ( name == "*" )
Sql_str="SELECT * FROM stocklive";
else
Sql_str="SELECT * FROM stocklive WHERE name='"+name+"'";
}
else if (cond=="V_datetime")
{
out.println("按日期时间查询:<br>");
datetime = request.getParameter("datetime");
if ( datetime == "*" )
Sql_str="SELECT * FROM stocklive";
else
Sql_str="SELECT * FROM stocklive WHERE datetime='"+datetime+"'";
}
Connection dbcon=DriverManager.getConnection(url,userID,passwd);
Statement dbcmd=dbcon.createStatement();
//Sql_str="SELECT * FROM stocklive";
ResultSet Qry=dbcmd.executeQuery(Sql_str);
if ( Qry.next() )
{
out.println("<center>代码:"+Qry.getString(1)+"</center><br>");
out.println("<center>名称:"+Qry.getString(2)+"</center><br>");
out.println("<center>日期时间:"+Qry.getString(3)+"</center><br>");
out.println("<center>成交价:"+Qry.getString(4)+"</center><br>");
out.println("<center>涨跌幅:"+Qry.getString(5)+"</center><br>");
out.println("<center>成交量:"+Qry.getString(6)+"</center><br>");
out.println("<center>收盘价:"+Qry.getString(7)+"</center><br>");
out.println("<center>开盘价:"+Qry.getString(8)+"</center><br>");
out.println("<center>最高价:"+Qry.getString(1)+"</center><br>");
out.println("<center>最低价:"+Qry.getString(1)+"</center><br>");
}
}
catch(Exception e)
{
out.println("查询失败!<br>");
e.printStackTrace();
}
%>
<html>
<meta http-equiv="Content-Type"; content="text/html;charset=GB2312">
<meta http-equiv="Content-Language"; content="ch-cn">
<head>
<title>
查询
</title>
</head>
<body background="image/bg04.jpg"><FONT color="red">
</body>
</html>
为什么对Sql_str变量无法赋值??????????????