First in the JSP page to judge and then jump __jsp

The effect of this example is that the selected value will pop up when any one of the radio boxes is chosen, and then jump to others.do;
When you do not select any of the radio boxes only pop-up prompts, do not jump, but stay on this page.

<script language= "JAVASCRIPT" >
<!--
function Check () {
var flag=0;
for (i=0;i<document.lin.r.length;i++) {
if (document.lin.r[i].checked) {
Alert ("Checked R" + (I+1));
flag=1;
return true;
}
}
if (flag==0) {
Alert ("no element checked");
return false;
}
}
-->
</SCRIPT>

<form name= "Lin" action= "others.do" >
<input type= "Radio" name= "R" > Left <input type= "Radio" name= "R" > Right <br/>
<input type= "Submit" value= "submitted" onclick= "return Check ()"/>
</from>