@EventHandler
    public void onBlockBreak(BlockBreakEvent event) {
        BlockState block = event.getBlock().getState();
        if (block instanceof Sign) {
            Sign sign = (Sign) block;
            if (!sign.getLine(0).equals("[Class]")) return;
            World world = event.getBlock().getWorld();
            int x = event.getBlock().getX();
            int y = event.getBlock().getY();
            int z = event.getBlock().getZ();
            String string = stringBuilder.BuildString(world, x, y, z);
            if (plugin.signSet.containsKey(string + "_exists")) {
                plugin.signSet.remove(string + "_exists");
            }
            Iterator<String> iterator = plugin.signSet.keySet().iterator();
            String s;
            while (iterator.hasNext()) { 
                s = iterator.next();
                if (s.startsWith(string)) {
                    iterator.remove();
                }
            }
        }
    }