public class ExampleGUI extends AbstractMenu {

    public ExampleGUI() {
        super(9, "&cExample GUI");
        ItemBuilder builder = BlizzardLibraryAPI.getLibraryAPI().getBuilderAccess().getItemBuilder();
        setItem(4, builder.itemType(Material.DIAMOND_SWORD).itemAmount(1).itemName("&cCool Diamond Sword").build(),
                player -> MessageAPI.sendFormattedMessage("&cYou just clicked the cool sword!"));
    }
}

//Example To Open The GUI
   @EventHandler
    public void onListener(BlockBreakEvent e) {
        final Player player = e.getPlayer();
        final Block block = e.getBlock();
        if (block.getType() == Material.DIAMOND_BLOCK) {
            new ExampleGUI().open(player);
        }
    }
}