Main.java

package com.thebukkitarea.inventories;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.inventory.InventoryAction;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.event.inventory.InventoryCloseEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.plugin.java.JavaPlugin;

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

/**
 * Created by אביתר on 06/01/2015.
 */
public class Main extends JavaPlugin implements Listener {

    private List<UUID> users = new ArrayList<UUID>();
    private  ItemStack _0 = createItemStack(Material.STAINED_GLASS_PANE, 1, (short) 15, ChatColor.GREEN + "It's good to be back."),
            _8 = createItemStack(Material.BOOK, 1, (short) 0, ChatColor.YELLOW + "THE BUKKIT AREA - 2k15");

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

    private Inventory getInventory() {
        Inventory inv = Bukkit.createInventory(null, 9, "Back to the channel");

        inv.addItem(_0);
        inv.setItem(8, _8);

        // 0, 1, 2, 3, 4, 5, 6, 7, 8

        return inv;
    }

    private ItemStack createItemStack(Material material, int amount, short durability, String name) {
        ItemStack stack = new ItemStack(material, amount, durability);

        ItemMeta meta = stack.getItemMeta();
        meta.setDisplayName(ChatColor.RESET + name);
        stack.setItemMeta(meta);

        return stack;
    }

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (sender instanceof Player) {
            Player player = (Player) sender;

            if (!users.contains(player.getUniqueId())) {
                users.add(player.getUniqueId());
            }

            player.openInventory(getInventory());
        }

        return true;
    }

    @EventHandler
    public void onInventoryClick(InventoryClickEvent event) {
        if (event.getWhoClicked() instanceof Player) {
            Player player = (Player) event.getWhoClicked();

            if (!users.contains(player.getUniqueId())) {
                return;
            }

            if (event.getCurrentItem() != null) {
                ItemStack current = event.getCurrentItem();
                event.setCancelled(true);

                if (current.equals(_0) && event.getSlot() == 0);
                else if (current.equals(_8) && event.getSlot() == 8);
                else {
                    event.setCancelled(false);
                }
            }
        }
    }

    @EventHandler
    public void onInventoryClose(InventoryCloseEvent event) {
        if (event.getPlayer() instanceof Player) {
            Player player = (Player) event.getPlayer();

            if (users.contains(player.getUniqueId())) {
                users.remove(player.getUniqueId());
            }
        }
    }
}