[HELP] Check if player is online

I'm now creating simple plugin, just to learn programming!
I want to check if player is online when i do /slay $player!

There's probably a better way, but this works.

PHP:

$isOnline = in_array($player,$this->getServer()->getOnlinePlayers());

$isOnline will return bool?

PHP:

public function isPlayerOnline($username){
   if($this->getServer()->getPlayer($username) instanceof Player){
      return true;
   }else{
      return false;
   }
}

Like @LDX said, there is probably a better way than this too, but it works, so yay!

These methods are too slow. You are looping through the players at least twice.

PHP:

$name = $args[0];
$player = $this->getServer()->getPlayer($name);
if($player instanceof Player){
  $player->setHealth(0);
  $sender->sendMessage("Slayed.");
}else{
  $sender->sendMessage("That player ain't online!");

Omg Tnx @PEMapModder i was using

PHP:

 if($player instanceof player/* Not "Player"*/){
}

Can't i use kill() instead of setHealth()?

Same.

I think yes. I forgot what setHealth() has over kill(). (Part of setHealth() calls kill() if health <= 0)