variable things..

** i am new at java**


so im trying to make a command that open custom inventory
so i made 2 classes ( there main class... but leave it for now)
1:

Code (Text):

package com.nktfh100.plugin;

import org.bukkit.Bukkit;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;


public class myCustomInventory {
    public static Inventory myInventory = Bukkit.createInventory(null, 9, "My custom Inventory!");
    // The first parameter, is the inventory owner. I make it null to let everyone use it.
    //The second parameter, is the slots in a inventory. Must be a multiple of 9. Can be up to 54.
    //The third parameter, is the inventory name. This will accept chat colors
    static {
        myInventory.setItem(0, new ItemStack(Material.DIAMOND, 1));
        myInventory.setItem(8, new ItemStack(Material.GOLD_INGOT, 1));
    }
    @EventHandler
    public void onInventoryClick(InventoryClickEvent event) {
    Player player = (Player) event.getWhoClicked(); // The player that clicked the item
    ItemStack clicked = event.getCurrentItem(); // The item that was clicked
    Inventory inventory = event.getInventory(); // The inventory that was clicked in
    if (inventory.getName().equals(myInventory.getName())) { // The inventory is our custom Inventory
    if (clicked.getType() == Material.DIRT) { // The item that the player clicked it dirt
    event.setCancelled(true); // Make it so the dirt is back in its original spot
    player.closeInventory(); // Closes there inventory
    player.getInventory().addItem(new ItemStack(Material.DIRT, 1)); // Adds dirt
    }
    }
    }
   
   
       


}

2:

Code (Text):

package com.nktfh100.plugin;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
public class cmdinv implements CommandExecutor {

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
         if (!(sender instanceof Player)) {
             sender.sendMessage(ChatColor.DARK_RED + "You're not a player!");
             return false;
        }
         sender.openInventory(myInventory);
        return false;
    }
}
 

but in the sender.openInventory(myInventory); it says: myInventory cant resolove to a variable..

i used this tutorial:
https://bukkit.org/threads/tutorial-create-a-inventory-menu.173571/

what i have done wrong?
please help me.
(sorry bad english)