public Long getDelta(String name, long count) {
        Long previous = lookup.put(name, count);
        return calculateDelta(name, previous, count);
    }
public Long getDelta ( String name , long count ) { Long previous = lookup . put ( name , count ) ; return calculateDelta ( name , previous , count ) ; }
Calculates the delta.  If this is a new value that has not been seen before, zero will be assumed to be the
initial value. Updates the internal map with the supplied count.

@param name  the name of the counter
@param count the counter value
@return the delta