public class Main extends JavaPlugin implements Listener {

    private ItemStack hide = new ItemStack(Material.INK_SACK, 1, (short) 8);
    {
        ItemMeta im4 = hide.getItemMeta();
        im4.setDisplayName(ChatColor.translateAlternateColorCodes('&', "HIDE ON"));
        hide.setItemMeta(im4);
    }
    private ItemStack show = new ItemStack(Material.INK_SACK, 1, (short) 10);
    {
        ItemMeta im4 = show.getItemMeta();
        im4.setDisplayName(ChatColor.translateAlternateColorCodes('&', "HIDE OFF"));
        show.setItemMeta(im4);
    }

    @Override
    public void onEnable() {
        Bukkit.getPluginManager().registerEvents(this, this);
    }

    @Override
    public void onDisable() {
    }

    @EventHandler
    public void onJoin(PlayerJoinEvent e) {
        if (e.getPlayer().getInventory().containsAtLeast(hide, 1)) {
            e.getPlayer().getInventory().remove(hide);

        }
        if (!e.getPlayer().getInventory().containsAtLeast(show, 1)) {
            e.getPlayer().getInventory().setItem(7, show);

        }
    }

    @EventHandler
    public void onInteract(PlayerInteractEvent e) {
        Player p = e.getPlayer();
        if (e.getHand() == EquipmentSlot.OFF_HAND) {
            return;
        }
        if (e.getAction() == Action.RIGHT_CLICK_AIR || e.getAction() == Action.RIGHT_CLICK_BLOCK) {
            if (p.getInventory().getItemInMainHand().getItemMeta().getDisplayName().equals("HIDE ON")) {

                for (Player all : Bukkit.getServer().getOnlinePlayers()) {

                    p.showPlayer(all);
                    p.getInventory().setItemInMainHand(show);
                    p.sendMessage("widoczny");
                    return;

                }
            }
            if (p.getInventory().getItemInMainHand().getItemMeta().getDisplayName().equals("HIDE OFF")) {

                for (Player all : Bukkit.getServer().getOnlinePlayers()) {

                    p.hidePlayer(all);
                    p.getInventory().setItemInMainHand(hide);
                    p.sendMessage("ukryty");
                    return;

                }

            }
        }
    }
}