In the JSP or Servlet that the form's action points to, you would use:
String[] vals = request.getParameterValues("val");
Then if you want to pass that in to your class, you could do like:
Calcs c = new Calcs();
c.setVal(vals);
Your class won't work as is, by the way, because you didn't give it a constructor:
public void Calcs()
{
//Default constructor
}