为什么这个JS几秒后会跳转，求解正确的写法？

Question

<script type="text/javascript">
function U_jump(Second, Url) {
if (--Second > 0) {
setInterval(U_jump(Second, Url),1000);
}
else {
location.href = Url; 
}
}
window.onload(U_jump(10, "/swlogin.aspx"));
</script>