Class

    public class DCase implemets Listener
    private static HashMap<String, Integer> keysofaccount = new HashMap<>();
    private int key = 0;
    //Другой код
    public static void open(Player p)
    {
        Inventory casE = Bukkit.createInventory(null, 9, ChatColor.RED + "Открыть кейс");
        ItemStack keyi = new ItemStack(131);
        ItemMeta meta = keyi.getItemMeta();
        List<String> list = new ArrayList<String>();
        String arg = "Ключей: " + keysofaccount.get(p.getName());
        list.add(arg);
        meta.setLore(list);
        meta.setDisplayName(ChatColor.GOLD + "ключ");
        keyi.setItemMeta(meta);
        casE.setItem(4, keyi);
        p.openInventory(casE);
    }

    public static void addKey(Player p,int amount)
    {
        keys = keys + amount;
        keysofaccount.put(p.getName(), keys);
    }

    public void removeKey(Player p)
    {
        keys = keys-1;
        keysofaccount.put(p.getName(), keys -1);
    }