Once in a discussion with my teacher about mechanical waves he told that in a system containing a wave generator and reflector, the node number $n$ between these two things will be always integer. Like this,
Then I said if the wave starts to propagate and I bring the reflector to a $2m$ distance, then the wave will squeez (make its wavelength short or long) enough to make integer numbered nodes.
However I don't see any logic in this. If one wave starts propagating then how can it change its wavelength in its path? So is it right or wrong?