Finding out how many players in a hashmap?

I am wondering how would I find out how many players are in a hashmap?
I am using this

Code:

public final HashMap <Player, ArrayList<Block>> lobby = new HashMap <Player, ArrayList<Block>>();

Thank you for reading!

 

BeefyPlays
lobby.size()

 

I get an error with this

Code:

@EventHandler(priority = EventPriority.LOW)
        public void Full(SignChangeEvent sign) {
            Player player = sign.getPlayer();
            if(sign.getLine(3).equalsIgnoreCase(ChatColor.BOLD + "4/4")) {
                player.sendMessage("ItsBeefu iz Amazing");
                sign.setLine(0, "" + ChatColor.DARK_RED + ChatColor.BOLD + "[Join]");
                sign.setLine(1, ChatColor.BOLD + "Sneaker Run");
                sign.setLine(2, ChatColor.BOLD + lobby.size());
                sign.setLine(3, ChatColor.BOLD + "Full Lobby");
                BukkitRunnable task = new BukkitRunnable() {
                        int countdown = 86;               
                        @Override
                        public void run(){
                        for(Player p : Bukkit.getOnlinePlayers()){
                        p.setLevel(countdown);
                        }
                        countdown--;
                        if (countdown < 0) {
                        this.cancel();
                        }
                        }
                        };
                        task.runTaskTimer(this, 0L, 20L);
            }
        }
    }

 

BeefyPlays
What is the error exactly?

 

BeefyPlays
If that's causing problems, you could try and simply iterate over the map, and check at each iteration if the player is null.