MuteCommand

public static List<Player> mutedPlayers = new ArrayList();

public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
    if(label.equalsIgnoreCase("mute")) {
        if(args.lenth == 1) {
            Player target = Bukkit.getPlayer(args[0]);
            if(target != null) {
                if(mutedPlayers.contains(target)) {
                    mutedPlayers.remove(target);
                    return true;
                } else {
                    mutedPlayers.add(target);
                    return true;
                }
            } else {
                sender.sendMessage("§4Invalid Arguments!");
                return false;
            }
        }
    }
    return false;
}