Run plugin when life is low

I want to make a plugin when life is low, I get some effects like:

Class Main extends PluginBase implements Listener {


public function onEnable() {
$this->getLogger()->info ("§aAtivado");
$this->getServer()->getPluginManager()->registerEvents($this,$this);
}

public function onDisable() {

$this->getLogger()->info('§aDesativado');

}




public function execute(Listener $listener, Event $event){
$p = $ev->getPlayer();
$health = getHealth();
if ($health <= 7) {
$p->sendTip('§dVocê usou o §aTOTEM');
$ev->getPlayer()->getInvenTory()->removeItem(Item::Get(341,0,1));
$p->addEffect(Effect::getEffect(10)->setAmplifier(3)->setDuration(10 * 3)->setVisible(true));
$p->addEffect(Effect::getEffect(11)->setAmplifier(1)->setDuration(5 * 1)->setVisible(true));
$p->addEffect(Effect::getEffect(12)->setAmplifier(1)->setDuration(5 * 1)->setVisible(true));
}
}

}​

but i don't know how to load even the public function

 

In my opinion there are two ways of doing that, if you want to check every second if a player has a specific number of hearts just create a Task and get all players of the server and check if they have x amount of hearts and if they have, for example lower than 3 hearts then give the player the effect you want to.

 

to track when damage is dealt use EntityDamageEvent, and make a request for execute()

function onDamage(EntityDamageEvent $event){
$entity = $event->getEntity();
if($event instanceof EntityDamageByEntityEvent){
if(($entity->getHealth() - $event->getFinalDamage()) <= 7){
$this->execute($entity);
}
}
}

function execute($p){
$p->sendTip('§dVocê usou o §aTOTEM');
$p->getInventory()->removeItem(Item::get(341, 0, 1));
$p->addEffect(Effect::getEffect(10)->setAmplifier(3)->setDuration(10 * 3)->setVisible(true));
$p->addEffect(Effect::getEffect(11)->setAmplifier(1)->setDuration(5 * 1)->setVisible(true));
$p->addEffect(Effect::getEffect(12)->setAmplifier(1)->setDuration(5 * 1)->setVisible(true));
}