nickname by SashPlays

Main.java:

package de.sashplays.Nick;

import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import org.bukkit.plugin.java.JavaPlugin;

public class Main extends JavaPlugin {

    @Override
    public void onEnable(){

        Bukkit.getPluginManager().registerEvents(new Nick(), this);
        this.getCommand("nick").setExecutor(new Nick());

    }
    @Override
    public void onDisable(){

        for(Player all : Bukkit.getOnlinePlayers()){
            new Nick();
            if(Nick.nick.containsKey(all.getName())){

                new Nick();
                new Nick();
                all.setPlayerListName(Nick.nickb.get(Nick.nick.get(all.getName())));
            }

        }

    }
}


Nick.java:

package de.sashplays.Nick;

import java.util.HashMap;

import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
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.AsyncPlayerChatEvent;
import org.kitteh.tag.PlayerReceiveNameTagEvent;
import org.kitteh.tag.TagAPI;

public class Nick implements CommandExecutor, Listener {

    static HashMap<String, String> nick = new HashMap<String, String>();
    static HashMap<String, String> nickb = new HashMap<String, String>();

    @EventHandler
    public void on (AsyncPlayerChatEvent e){

        Player p = e.getPlayer();

        if(nick.containsKey(p.getName())){

            e.setFormat(ChatColor.translateAlternateColorCodes('&', nick.get(p.getName()))+" | "+ e.getMessage());
        }
    }
    @EventHandler
    public void on(PlayerReceiveNameTagEvent e){
        Player p = e.getNamedPlayer();
        Player pl = e.getPlayer();

        if(nick.containsKey(p.getName())){

            e.setTag(ChatColor.translateAlternateColorCodes('&', nick.get(p.getName())));
        }
    }

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String arg2,
            String[] args) {

        Player p = (Player)sender;

        if(cmd.getName().equalsIgnoreCase("nick")){
            if(args.length == 0){
                p.sendMessage("§b/Nick <name>");
            }else{
            if(args.length == 1){

                String name = args[0];
                nick.put(p.getName(), name);
                nickb.put(name, p.getName());
                name = ChatColor.translateAlternateColorCodes('&', name);
                TagAPI.refreshPlayer(p);
                p.setPlayerListName(name);

                p.sendMessage("§aDu heißt jetzt "+name+".");


            }
            }
        }

        return true;

    }


    }