well, holes are taken to be positively charged and travel from p to n layer so that is the direction of conventional current(direction of flow of proton) and hence it is taken as the direction of current so the direction of the arrow head of the diode gives the direction of current in forward bias and the other way around for reverse bias
The direction of arrow head shows the conventional direction of current flow,that is from +ve to -ve.. But the actual flow of electron will be opposite to this.. Just go through the basics in semi conductor device and you will be able to understand it much better..
a diode restricts the direction of charge carriers movement, allowing an electric current to flow in one direction, but blocks it in the opposite direction.
the diode can be thought of as an electronic version of a check valve.
its current direction is indicated by the arrow directly (for conventional direction)
whereas the electrons direction is the opposite of course