<%--
Document : index
Created on : 2009-4-17, 12:06:51
Author : Administrator
--%><%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd"><html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<%
try
{
/*
if(request.getParameter("action")==null || request.getParameter("action")=="")
{
out.print("sdfsdfsdfsd");
}
*////*
if(request.getParameter("action")!=null || request.getParameter("action")!="")
{
out.println(request.getParameter("action"));
}
else
{
out.println("Not action");
}
if(request.getParameter("username")!=null)
{
out.println(request.getParameter("username"));
}
else
{
// */
%>
<form name="form1" method="get">
<input type="text" name="username" value="" />
<input type="hidden" name="action" value="my name is 莫逆" /> <input type="submit" value="Submit" name="submit" />
</form>
<% ///*
}
//*/
}
catch(Exception e)
{
out.println("出错了!<br>");
out.println(e.getMessage()+"<br>");
out.println(e.getLocalizedMessage());
} %> </body>
</html>为什么页面会显示
null
和一个输入和按钮框,我上面明明判定了不等于null的,
Document : index
Created on : 2009-4-17, 12:06:51
Author : Administrator
--%><%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd"><html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<%
try
{
/*
if(request.getParameter("action")==null || request.getParameter("action")=="")
{
out.print("sdfsdfsdfsd");
}
*////*
if(request.getParameter("action")!=null || request.getParameter("action")!="")
{
out.println(request.getParameter("action"));
}
else
{
out.println("Not action");
}
if(request.getParameter("username")!=null)
{
out.println(request.getParameter("username"));
}
else
{
// */
%>
<form name="form1" method="get">
<input type="text" name="username" value="" />
<input type="hidden" name="action" value="my name is 莫逆" /> <input type="submit" value="Submit" name="submit" />
</form>
<% ///*
}
//*/
}
catch(Exception e)
{
out.println("出错了!<br>");
out.println(e.getMessage()+"<br>");
out.println(e.getLocalizedMessage());
} %> </body>
</html>为什么页面会显示
null
和一个输入和按钮框,我上面明明判定了不等于null的,
应该是:if(request.getParameter("username")!=null || request.getParameter("username")!="")这样吧?呵呵!
{
out.println(request.getParameter("action"));
}
else
{
out.println("Not action");
}
应该是这段打出来的,不应该用 || 应该用 &&,因为你的request.getParameter("action")=null,所以request.getParameter("action")!="" 为true,你用||的话,request.getParameter("action")!=null || request.getParameter("action")!=""为true,所以会打出null来。
if(request.getParameter("action")==null || request.getParameter("action").equals("")){
//具体操作...
}
不能用等号,只能用它里面的方法equals()
if(request.getParameter("action")!=null || !request.getParameter("action").equals("")){
//具体操作...
}
not do;
else
do;
可是为什么呢我把||改成&&会是会输出else下面的内容然后我又改回来,尔后又改变request.getParameter("action").equals("")
会输出异常错误的
请各位再次详细好吗,以前没有注意这样的问题??
string类型的是对象比较应该用equals 而不能用==