how to get closest player/entity to player?

so, like the title says im trying to get the closest player/entity to the player themselves. Im v new to modding minecraft so not really sure what everything does. Iv tried searching everywhere and watching quite a few modding tutorials but nothing seems to be helping. Any help would be appreciated, thanks.

not sure how to structure the parameters for level.getNearbyPlayers so thats why it's blank

apparently needs 3 arguments including TargetingConditions, LivingEntity and AABB but im not sure how to structure them.

this is the code:

public class getClosest{
    public double nearbyPlayers (Entity player, Level level, LivingEntity living){
        level.getNearbyPlayers();
    }

}