Poboczna klasa

List<UUID> channel = new ArrayList<>();

public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
  if(label.equalsIgnoreCase("channel")) {
    if(sender instanceof Player) {
      Player player = (Player) sender;
      if(player.hasPermission("echat.channel")) {
        if(args[0].equalsIgnoreCase("join")) {
          if(!(channel.contains(player.getUniqueId()))) {
            channel.add(player.getUniqueId());
            player.sendMessage("You has been connected to the channel");
          } else {
            player.sendMessage("You're already connected to the channel");
          }
        }
        if(args[0].equlsIgnoreCase("leave")) {
          if(channel.contains(player.getUniqueId())) {
            channel.remove(player.getUniqueId());
            player.sendMessage("You has been disconnected from the channel");
          } else {
            player.sendMessage("You're not connected to any channel");
          }
        }
      } else {
        player.sendMessage("You don't have permission to this");
      }
    } else {
      sender.sendMessage("This command can be used only from in-game state");
    }
    return true;
  }
}

@EventHandler
public void chatEvent(AsyncPlayerChatEvent e) {
  if(channel.contains(e.getPlayer().getUniqueId())) {
    e.setCancelled(true);
    for(Player player : Bukkit.getServer().getOnlinePlayers()) {
      if(player.hasPermission("echat.channel.admin")) {
        player.sendMessage(e.getMessage());
      } else {
        if(channel.contains(player.getUniqueId())) {
          player.sendMessage(e.getMessage());
        }
      }
    }
  }
}