ArrayList<String> staff = new ArrayList<String>();

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if(label.equalsIgnoreCase("staff")){
            Player p = (Player) sender;

            staff.add("crafttim");
            staff.add("Kirral");
            staff.add("IxaroS");

            Inventory inv = Bukkit.createInventory(null, 54, "§cStaff");

            String online = "§cnon";
            String grade = "joueur";

            for(String s : staff) {

                if(Bukkit.getPlayer(s) != null) {

                    online = "§aoui";
                }

                ItemStack item = new ItemStack(Material.SKULL_ITEM, 1, (byte) 3);
                SkullMeta meta = (SkullMeta) item.getItemMeta();
                meta.setDisplayName(s);
                meta.setLore(Arrays.asList("§fGrade : "+grade, "§fEn ligne : "+online));
                meta.setOwner(s);
                item.setItemMeta(meta);

                inv.addItem(item);
            }

            p.openInventory(inv);
        }
        return false;
    }