Code plugin admintchat

package fr.skorpio.adminchat;

import java.util.ArrayList;

import org.bukkit.Bukkit;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.event.player.PlayerKickEvent;
import org.bukkit.plugin.java.JavaPlugin;

import net.md_5.bungee.api.ChatColor;

public class Main extends JavaPlugin implements Listener {

    String argumentmessage = ChatColor.RED + "Merci de rentrer un argument !";
    String erreurmessage = ChatColor.RED + "Erreur : ce n'est pas la bonne syntaxe!";
    String NoPermissionErreur = ChatColor.RED + "Erreur : tu n'as pas la permission d'effectuer cette commande !";
    String AdminTchat = ChatColor.RED + "AdminTchat";

    ArrayList<Player> OnlineAdmin = new ArrayList<Player>() ;


    @Override
    public void onEnable() {
        getLogger().info("AdminTchat activé !");
        getCommand("admintchat").setExecutor(this);
        Bukkit.getServer().getPluginManager().registerEvents(this, this);
    }

    @Override
    public void onDisable() {
        getLogger().info("AdminTchat désactivé !");

    }

    @EventHandler
    public void OnJoinPlayer(PlayerJoinEvent pje){
        Player AdminOnline = pje.getPlayer();
        if(!OnlineAdmin.contains(AdminOnline)){
            if(AdminOnline.hasPermission(new Permissions().AdminTchatUse)){
                OnlineAdmin.add(AdminOnline);
                AdminOnline.sendMessage(ChatColor.GREEN + "Tu es connectés à l'AdminTchat du serveur !");
            }
        }

    }

    @EventHandler
    public void OnKickPlayer(PlayerKickEvent pke){
        Player AdminPlayer = pke.getPlayer();
        if(OnlineAdmin.contains(AdminPlayer)){
            OnlineAdmin.remove(AdminPlayer);;
        }

    }

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if(label.equalsIgnoreCase("admintchat") && sender instanceof Player){
            Player player = (Player) sender;

            if(args.length < 1){
                player.sendMessage(argumentmessage);
        }else if(args.length >= 1){
            if(player.hasPermission(new Permissions().AdminTchatUse)){

                String msg = String.join("", args);

                for(Player p : OnlineAdmin) {
                    p.sendMessage(AdminTchat + "$c($S" + player.getName() + "$c)" + ChatColor.GRAY + "--> " + ChatColor.GREEN + "You" + ChatColor.GRAY + ": " + ChatColor.WHITE + msg);
                }
            }else {
                player.sendMessage(NoPermissionErreur);
            }
        }

        }
        return false;
    }
}