SnowBall Potion Effects

So I Have a idea If Someone Gets hit by a snowball they get a potion effect But I couldn't seem to figure it out
I started with EntityDamageByEntityEvent But got no where from their (Im new to deving and don't understand much)

 

EntityDamageByEntityEvent
EntityDamageEvent.DamageCause.PROJECTILE

 

??

 

@EventHandler
public void onHit(EntityDamageByEntityEvent e) {
if(the cause EntityDamageEvent.DamageCause.PROJECTILE) {
// your code

 

ok so

@EventHandler
public void onHit(EntityDamageByEntityEvent e) {
if(the cause EntityDamageEvent.DamageCause.PROJECTILE) {
then add the potion effect here

would this all be in the main???

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

Yeah that would be it, just make it work for scenario add your checks in and everything