static HashMap<Player, Long> playtime = new HashMap<>();

public interface Callback<T>{
    public void execute(Long response);
}

public static void doAsyncGetPlaytime(final Player p, final Callback<Boolean> callback){
    new BukkitRunnable(){

        @Override
        public void run(){


            playtime.put(p, 0L);
            try{
                PreparedStatement ps = plugin.MySQL.openConnection().prepareStatement("SELECT playtime FROM users WHERE UUID='"+p.getUniqueId().toString()+"'");
                ResultSet rs = ps.executeQuery();
                if(rs.next()){
                    playtime.put(p, rs.getLong("playtime"));
                }
                rs.close();
            }catch(Exception ex){
                ex.printStackTrace();
            }

            new BukkitRunnable()
            {
                @Override
                public void run()
                {
                    callback.execute(playtime.get(p));
                }
            }.runTask(plugin);
        }
    }.runTaskAsynchronously(plugin);
}

Callback<Long> callback = new Callback<Long>()
    {
        public void execute(Long l)
        {
            return l;
        }
    };