Trying to use delayed tasks in a repeating task

I'm trying to initiate a 10 second countdown every 5 minutes without lagging the server.

Here is my code:

Code:

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
     
        if (args[0].equalsIgnoreCase("start")) {
            @SuppressWarnings("unchecked")
            Collection<Player> players = (Collection<Player>) Bukkit.getOnlinePlayers();

            if (players.size() != 2) {
                sender.sendMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.RED + "There must be 2 players for death swap!"));
                return true;
            }
         
            int sec = (int) 20L;
            plugin.getServer().getScheduler().scheduleSyncRepeatingTask(plugin, DeathSwapCommand::scheduleSwap, sec * 270, sec * 300);

            Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.GREEN + "Swapping in 5 minutes."));
        } else {
            sender.getServer().getScheduler().cancelTasks(plugin);
            sender.sendMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.GREEN + "Stopped swapping."));
        }
     
        return true;
    }
 
    public static void scheduleSwap() {

        @SuppressWarnings("unchecked")
        List<Player> players = (List<Player>) Bukkit.getOnlinePlayers();
     
        Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.RED + "Swapping in 30 seconds."));
     
        int sec = (int) 20L;

        plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new Runnable() { public void run() {} }, sec * 20);
     
     
        for (int i = 10; i > 1; i--) {
            Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.RED + "Swapping in " + i + " seconds!"));

            plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new Runnable() { public void run() {} }, sec);
        }
     
        Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.RED + "Swapping in 1 second!"));
     
        plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new Runnable() { public void run() {} }, sec);
     
        Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.RED + "Swap now."));
        Location player0 = players.get(0).getLocation();
        Location player1 = players.get(1).getLocation();

        players.get(0).teleport(player1);
        players.get(1).teleport(player0);
    }

Instead of properly sending a message with 30 seconds left and then a 10 second count down, it sends all 11 messages at the same time, at the same time of teleportation of players. How do I fix this?

Notice the times of these messages are all the same: https://i.imgur.com/woMtwzd.png


I don't know how to format code on this website so the indents are messed up but hopefully it's still readable

 

This line does nothing. You call it 3 times. Notice the empty run method.

PHP:

plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new Runnable() { public void run() {} }, sec * 20);

Your code gives me the impression you don't know how a scheduler works.
scheduleSyncRepeatingTask takes delay and period (final 2 parameters) as ticks, so you schedule the entirety of scheduleSwap to run every 1,4 seconds or so, after a 15 second delay.
You see all the messages at once because you send them all at once in this loop:

PHP:

for (int i = 10; i > 1; i--) {
            Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', ChatColor.RED + "Swapping in " + i + " seconds!"));

            plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new Runnable() { public void run() {} }, sec);
        }

The scheduled task there does nothing.

 

The problem is that variables inside a Runnable must be final so I can't use "i" to count down to 1 second. Also how is it running the whole thing in 1.4 seconds? Please explain


Edit: I now understand that only the code in the runnable is delayed and after that line, everything is immediately run, not delayed.

I fixed the final issue using this: https://bukkit.org/threads/create-a-simple-countdown.372228/

Solved!

 

I said it runs it every 1.4 seconds, not that it ran in 1.4 seconds, and this is readily apparent.

 

1. make a BukkitRunnable that will run every 5 minutes
2. make the runnable run a method that will run every 20 ticks