GUI only showing kits you have access to

Hey guys, still doing this GUI, I think I have it all figured out besides somethings.

Code:java

Knight {
        public void give(Player p) {
            Utils.clearInv(p);
            PlayerInventory inv = p.getInventory();
            ItemStack pvp = new ItemStack(Material.DIAMOND_SWORD);
            pvp.addEnchantment(Enchantment.DAMAGE_ALL, 1);
            inv.addItem(pvp);
            inv.setHelmet(new ItemStack(Material.IRON_HELMET));
            inv.setChestplate(new ItemStack(Material.IRON_CHESTPLATE));
            inv.setLeggings(new ItemStack(Material.IRON_LEGGINGS));
            inv.setBoots(new ItemStack(Material.IRON_BOOTS));
            Utils.giveSoup(p);
        }
 
        public String getPermission() {
            return "k.knight";
        }
 
        public String getName() {
            return "Knight";
        }
 
 
        public ItemStack kitgui(Material type) {
            ItemStack knight = new ItemStack(Material.DIAMOND_SWORD);
            ItemMeta knightmeta = knight.getItemMeta();
            knightmeta.setDisplayName(ChatColor.GOLD + "Knight Kit");
            return knight;
 
        }
}
public abstract void give(Player p);
 
    public abstract String getPermission();
 
    public abstract String getName();
 
    public abstract ItemStack kitgui(Material type);

In my GUI, How would I get the kitgui method to add the itemstack to the gui if they have permission?

 

Code:

if(player.hasPermission("a permission") {
    inventory.addItem(someItemStack);
}