@EventHandler
public void bombSymptom (PlayerInteractEvent event) throws InterruptedException{
    final Player player = event.getPlayer();
    if (player == Bukkit.getPlayer("Viktoracri") && event.getItem() != null && event.getItem().getType() == Material.PUMPKIN && player.isOnGround() && player.getHealth() == 20){
        Location loc = event.getPlayer().getLocation();
        player.addPotionEffect(new PotionEffect(PotionEffectType.DAMAGE_RESISTANCE, 100, 10));
        event.getPlayer().getWorld().createExplosion(loc, 3);
        player.setHealth(15);
        //Wait 1 sec
        player.setHealth(16);
        //Wait 2 sec
        player.setHealth(17);
        //Wait 1 sec
        player.setHealth(18);
        //Wait 1 sec
        player.setHealth(19);
    }
}

final int run = Bukkit.getScheduler().scheduleSyncRepeatingTask(Core.getPlugin(), new Runnable()
{
    int i = 0;
    @Override
    public void run()
    {
        if (i > 4)
            Bukkit.getScheduler().cancelTask(run);
        player.setHealth(i + 15);
        i++;
    }
}, initDelay, loopDelay);

public class BombThread implements Runnable {

    public Player p;

    public BombThread (Player p) {
        this.p = p;
    }

    public void run() {
        p.setHealth(15);
        Thread.sleep(1000);
        p.setHealth(16);
        Thread.sleep(2000);
        p.setHealth(17);
        Thread.sleep(1000);
        p.setHealth(18);
        Thread.sleep(1000);
        p.setHealth(19);
    }
}

BombThread thread = new BombThread(player);
thread.start();