Plugin fout

package me.notchapplee.playerhider;

import java.util.ArrayList;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.Action;
import org.bukkit.event.player.PlayerInteractEvent;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.plugin.java.JavaPlugin;

public class Main extends JavaPlugin implements Listener {

        private ArrayList<String> usingClock;

        public void onEnable() {
                Bukkit.getServer().getPluginManager().registerEvents(this, this);

                this.usingClock = new ArrayList<String>();
        }

        @EventHandler
        public void onPlayerInteract(PlayerInteractEvent e) {
                if (e.getAction() != Action.RIGHT_CLICK_AIR && e.getAction() != Action.RIGHT_CLICK_BLOCK) {
                        return;
                }

                if (e.getItem().getType() != Material.WATCH) {
                        return;
                }

                if (
                                !e.getItem().hasItemMeta() ||
                                !e.getItem().getItemMeta().hasDisplayName() ||
                                !e.getItem().getItemMeta().getDisplayName().equals("\u00a7e\u00a7lSpelers \u00a77: \u00a7a\u00a7lAan \u00a77\u00a7l/ \u00a7c\u00a7lUit")
                ) {
                        return;
                }

                if (usingClock.contains(e.getPlayer().getName())) {
                        usingClock.remove(e.getPlayer().getName());
                        e.getPlayer().sendMessage(ChatColor.GREEN + "\u00a77[\u00a7c\u00a7elHGH\u00a77] Spelers staan nu aan!");
                        for (Player p : Bukkit.getServer().getOnlinePlayers()) {
                                if (p != e.getPlayer()) {
                                        e.getPlayer().showPlayer(p);
                                }
                        }
                }

                else {
                        usingClock.add(e.getPlayer().getName());
                        e.getPlayer().sendMessage(ChatColor.RED + "\u00a77[\u00a7c\u00a7elHGH\u00a77] Spelers staan nu uit!");
                        for (Player p : Bukkit.getServer().getOnlinePlayers()) {
                                if (p != e.getPlayer()) {
                                        e.getPlayer().hidePlayer(p);
                                }
                        }
                }
        }

        @EventHandler
        public void onPlayerJoin(PlayerJoinEvent e){
                ItemStack magicClock = new ItemStack(Material.WATCH, 1);

                ItemMeta magicClockMeta = magicClock.getItemMeta();
                magicClockMeta.setDisplayName("\u00a7e\u00a7lSpelers \u00a77: \u00a7a\u00a7lAan \u00a77\u00a7l/ \u00a7c\u00a7lUit");
                magicClock.setItemMeta(magicClockMeta);

                e.getPlayer().getInventory().clear();
                e.getPlayer().getInventory().addItem(magicClock);

                for (Player p : Bukkit.getServer().getOnlinePlayers()) {
                        if (p != e.getPlayer()) {
                                if (usingClock.contains(p.getName())) {
                                        p.hidePlayer(e.getPlayer());
                                }

                                else {
                                        p.showPlayer(e.getPlayer());
                                }
                        }
                }
        }
}