Working Code

package me.Eekelmo.GUITP;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.Action;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.event.player.PlayerInteractEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.plugin.java.JavaPlugin;

public class gui extends JavaPlugin implements Listener {
	// Enable
	@Override
	public void onEnable() {
		getServer().getPluginManager().registerEvents(this, this);
		getLogger().info("-------- GUI TP by Eekelmo enabled -------");
	}

	// Disable
	@Override
	public void onDisable() {
		getLogger().info("-------- GUI TP by Eekelmo disabled -------");
	}

	// Teleport thing
	private void teleportInWorld(Player player, int x, int y, int z) {
		player.teleport(new Location(player.getWorld(), x, y, z));

	}

	private void openGUI(Player player) {
		Inventory inv = Bukkit.createInventory(null, 9, ChatColor.GREEN + "World Selector");
		// Main world
		ItemStack mainworld = new ItemStack(Material.NETHER_STAR);
		ItemMeta mainworldMeta = mainworld.getItemMeta();
		// Mining
		ItemStack miningworld = new ItemStack(Material.DIAMOND_PICKAXE);
		ItemMeta miningworldMeta = miningworld.getItemMeta();
		// Setting text
		mainworldMeta.setDisplayName(ChatColor.DARK_RED + "Main");
		mainworld.setItemMeta(mainworldMeta);
		// Setting text
		miningworldMeta.setDisplayName(ChatColor.GREEN + "Mining");
		miningworld.setItemMeta(miningworldMeta);
		// Setting placement
		inv.setItem(3, mainworld);
		inv.setItem(5, miningworld);
		// Opening
		player.openInventory(inv);
	}

	@EventHandler
	public void onInventoryClick(InventoryClickEvent event) {
		if (!ChatColor.stripColor(event.getInventory().getName()).equalsIgnoreCase("World Selector"))
			return;
		Player player = (Player) event.getWhoClicked();
		event.setCancelled(true);

		if (event.getCurrentItem() == null || event.getCurrentItem().getType() == Material.AIR
				|| !event.getCurrentItem().hasItemMeta()) {
			player.closeInventory();
			return;
		}

		switch (event.getCurrentItem().getType()) {
		case NETHER_STAR:
			teleportInWorld(player, -1034, 76, -849);
			player.closeInventory();
			event.setCancelled(true);
			player.sendMessage(String.format("&sTeleported to the &sMain World&s!", ChatColor.GOLD, ChatColor.DARK_RED, ChatColor.GOLD));
			break;
			case DIAMOND_PICKAXE:
				teleportInWorld(player, -945, 69, -873);
				player.closeInventory();
				event.setCancelled(true);
				player.sendMessage(String.format("&sTeleported to the &sMining World&s!", ChatColor.GOLD, ChatColor.GREEN, ChatColor.GOLD));
				break;
				default:
					player.closeInventory();
					break;
		}
		}







	@EventHandler
	public void onPlayerInteract(PlayerInteractEvent event) {
		Action a = event.getAction();
		ItemStack is = event.getItem();
		if (a == Action.PHYSICAL || is == null || is.getType() == Material.AIR)
			return;
		if(is.getType() == Material.COMPASS)
			getLogger().info("Compass used successfully");
			openGUI(event.getPlayer());
	}

}