Entity falling distance is the distance the entity have fallen without reaching a block.

It can be used to calculate different damage from falling, or activating an effect after a big fall.

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Retrieving the falling distance

float distanceFell = entity.getFallingDistance();

Setting the falling distance

This can be used to simulate a different falling distance than the real one. Bukkit will calculate the damage using the new falling distance.

entity.setFallingDistance(float distance);

You can cancel a fall damage by using the EntityDamageEvent

@EventHandler
public void onEntityDamage(EntityDamageEvent e) {
Entity tookDamage = e.getEntity();

DamageCause cause = e.getCause();

if (cause == DamageCause.FALL){
   //Damage was caused by falling, cancel it
   e.setCancelled(true);
}