I am trying to generate random number in textbox when click submit button

<form action="#">

<%
Random random=new Random();
int num=random.nextInt();
%>

Random Number:<input type="text" value="<%=num %>"/><br/>
<input type="submit" value="RandomNumberGenerator"/>
</form>

When page is reload random number is generate in textbox.but when i click RandomNumberGenerator button it can not generate random number.How to generate random number when i click RandomNumberGenerator Button.