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

        for(int i = 0; i < staff.size(); i++){
            String online = "§cnon";
            String grade = "joueur";

            if(Bukkit.getPlayer(staff.get(i)) != null){
                online = "§aoui";
            }

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

            inv.addItem(skull);

            if(i == inv.getSize()){
                break;
            }
        }
        p.openInventory(inv);