jQuery datepicker() Uncaught TypeError: undefined is not a function

Can anyone please help me I am struggling with this problem for the past few day. Actually I included all the necessary plugins' but still the

$('#datepicker').datepicker() function is not defined ERROR.

I included the same plugins' in the other jsp of my projects there the datepicker works perfectly.

This is what I tried.

<script src="http://code.jquery.com/jquery-1.10.2.js"></script>
<script src="http://code.jquery.com/ui/1.10.4/jquery-ui.js"></script>
<link rel="stylesheet" href="http://code.jquery.com/ui/1.10.4/themes/smoothness/jquery-ui.css">

$( '#datepicker' ).datepicker();

It throws the exception on page load itself. Thanks.