Fetching values returned by functions from Free Marker template in Java -

How can I get the function returned by the function in the free marker template and use it in Java?

This is the code I am using in FMT:

  & lt; #function avg x y> & Lt; #return (x + y) / 2 & gt; & Lt; / # Function & gt; $ {Avg (10, 20)}  

How can I use this function in Java?