一段计算加减乘除的编码能运行 为什么不能计算 ？？
<html><head>
<title></title>
<%@ page contentType="text/html;chraset=gb2312" language="java" errorPage="" %>
</head>
<body>
<%
int result=0;
String num1,num2;
num1=request.getParameter("x");
num2=request.getParameter("y");
String value=request.getParameter("select");
if(value=="+")
{result=Integer.parseInt(num1)+Integer.parseInt(num2);}
else if(value=="-")
{result=Integer.parseInt(num1)-Integer.parseInt(num2);}
else if(value=="*")
{result=Integer.parseInt(num1)*Integer.parseInt(num2);}
else if(value=="/")
{result=Integer.parseInt(num1)/Integer.parseInt(num2);}
%>
<form method="post" action="mains.jsp">
<input type="text" name="num1" value="">
<select name="select">
<option value="+">+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type="text" name="num2" value="">
<input type="submit" value="=" >
<%=result%>
</form>
</body>
</html>
跪求答案 希望哪位大哥大姐 能帮忙解决
