ScoreboardManager.java

public class ScoreboardManager implements Listener
{
    private static Map<Player, ScoreboardSign> map = new HashMap<>();
    private static String name = "MyGame";

    @EventHandler
    public void onQuit(PlayerQuitEvent e)
    {
        if(map.contains(e.getPlayer())
            map.remove(e.getPlayer());
    }

    public static ScoreboardSign create(Player player)
    {
        ScoreboardSign sign = new ScoreboardSign(player, name);
        sign.create();
        map.put(player, sign);
        return sign;
    }

    public static ScoreboardSign get(Player player)
    {
        if(map.get(player) == null)
            create(player);

        return map.get(player);
    }

    public static void setSidebarName(String newName)
    {
        name = newName;
    }
}