Gui plugin not making a gui

I have made a plugin for a custom GUI but it is not working.
The plugin gets loaded on my server but when i run the command to open the GUI nothing happens.
It does not even throw an error at all.

This is the utils class.

Code:

package com.hn_hosting.gui.utils;

import java.util.ArrayList;
import java.util.List;

import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

public class Utils {
   
   public static String chat (String s) {
     return ChatColor.translateAlternateColorCodes('&', s);
   }
   
   public static ItemStack createItem(Inventory inv, int materialId, int amount, int invSlot, String displayName, String... loreString) {
     
     ItemStack item;
     List<String> lore = new ArrayList();
     
     item = new ItemStack(Material.getMaterial(materialId), amount);
     
     ItemMeta meta= item.getItemMeta();
     meta.setDisplayName(Utils.chat(displayName));
     for (String s : loreString) {
       lore.add(Utils.chat(s));
     }
     meta.setLore(lore);
     item.setItemMeta(meta);
     
     inv.setItem(invSlot - 1, item);
     return item;
     
   }
   
public static ItemStack createItemByte(Inventory inv, int materialId, int byteId, int amount, int invSlot, String displayName, String... loreString) {
     
     ItemStack item;
     List<String> lore = new ArrayList();
     
     item = new ItemStack(Material.getMaterial(materialId), amount, (short) byteId);
     
     ItemMeta meta= item.getItemMeta();
     meta.setDisplayName(Utils.chat(displayName));
     for (String s : loreString) {
       lore.add(Utils.chat(s));
     }
     meta.setLore(lore);
     item.setItemMeta(meta);
     
     inv.setItem(invSlot - 1, item);
     return item;
     
   }
   
}

and this is the Ui class.

Code:

package com.hn_hosting.gui.ui;

import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;

import com.hn_hosting.gui.utils.Utils;

public class Ui {
   
   public static Inventory inv;
   public static String inventory_name;
   public static int inv_rows = 4 * 9;
   
   public static void initialize() {
     inventory_name = Utils.chat("&6&lTest");
     
     inv = Bukkit.createInventory(null, inv_rows);
   }

   public static Inventory GUI (Player p) {
     Inventory toReturn = Bukkit.createInventory(null,  inv_rows, inventory_name);
     
     Utils.createItem(inv, 4, 1, 1, "&cTest Item", "Just a test");
     
     toReturn.setContents(inv.getContents());
     return toReturn;
   }
   
   public static void clicked(Player p, int slot, ItemStack clicked, Inventory inv) {
     if (clicked.getItemMeta().equalsIgnoreCase(Utils.chat("&cTest Item"))) {
       p.setDisplayName(Utils.chat("ok then"));
     }
   }
}

I just need to know what i am doing wrong.

 

That is because my Gui never pops up like it should

 

It's a method that you call using a player object, you have created your custom inventory with your custom items, now what you need to do is choose what players you want the gui to open for and use that method. You will find the method you are looking for here.