Changing items in a GUI constantly on a Runnable

Code:

private void openGUI(Player p) {
        inv = Bukkit.createInventory(null, 9, ChatColor.AQUA
                + "Teleport");
        new BukkitRunnable(){
            public void run(){
                if(num == 1){
                    ItemStack is = new ItemStack(Material.STAINED_GLASS_PANE, 1, (short)15);
                    ItemStack is2 = new ItemStack(Material.STAINED_GLASS_PANE, 1, (short)0);
                    inv.setItem(0, is);
                    inv.setItem(1, is2);
                num++;
                }
                else
                        if(num == 2){
                            ItemStack is = new ItemStack(Material.STAINED_GLASS_PANE, 1, (short)15);
                            ItemStack is2 = new ItemStack(Material.STAINED_GLASS_PANE, 1, (short)0);
                            inv.setItem(0,is2);
                            inv.setItem(1,is);
                        num = 0;  
                }
            }
        }.runTaskTimer(Hub.getInstance(), 0, 20);

I want the glass to flicker between spots. I just did the first 2 slots for testing purposes. Don't know the error, seeking help . Thanks for taking the time to read

 

What exactly is the problem?

 

The glass appears on the first click after a reload, but doesn't flicker, then doesn't appear at all.

 

@kraazeekid On the second one, you're setting num to 0, but you check if num is 1 or 2.

 

@kraazeekid

That is because unless you're saving the instance in a file, the instance is not saved, and thus after the reload it won't work. You can't get around it.

 

@kraazeekid You should use booleans for this:

Code:

boolean name = false;
name = !name;
if (name) {
    // Set to spot 1
} else {
    // Set to spot 2
}

 

I used a boolean and it didn't work.