Kicking players from arraylist.

I'm running into a problem with the current code:

Code:java

public ArrayList<Player> playing = new ArrayList<Player>();
public ArrayList<Player> redTeam = new ArrayList<Player>();
public ArrayList<Player> blueTeam = new ArrayList<Player>();
 
..
 
private void kick() {
    if (!(playing.isEmpty())) {
        for (Player p : playing) {
            if (this.redTeam.contains(p))
                this.redTeam.remove(p);
            if (this.blueTeam.contains(p))
                this.blueTeam.remove(p);
 
            this.playing.remove(p);
            this.getLogger().info("Player " + p + " has been kicked.");
            p.sendMessage(ChatColor.RED + "You have been kicked from the game!");
        }
    }
}

What I do is when the plugin/server is reloaded, I will kick everyone from the game, so nothing will mess up, but an exception occurs whenever there is a player in the list at all. The error is a java.util.ConcurrentModificationException which I have not encountered before until now. The error is thrown at for (Player p : playing) and I don't know why.

Full Stack Trace:

Code:

06:13:50 [SEVERE] Error occurred while disabling ExtremePaintball v0.0.1 (Is it
up to date?)
java.util.ConcurrentModificationException
        at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
        at java.util.ArrayList$Itr.next(Unknown Source)
        at me.shzylo.extremepaintball.ExtremePaintball.kick(ExtremePaintball.jav
a:95)
        at me.shzylo.extremepaintball.ExtremePaintball.onDisable(ExtremePaintbal
l.java:42)
        at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:219)
        at org.bukkit.plugin.java.JavaPluginLoader.disablePlugin(JavaPluginLoade
r.java:481)
        at org.bukkit.plugin.SimplePluginManager.disablePlugin(SimplePluginManag
er.java:400)
        at org.bukkit.plugin.SimplePluginManager.disablePlugins(SimplePluginMana
ger.java:393)
        at org.bukkit.plugin.SimplePluginManager.clearPlugins(SimplePluginManage
r.java:434)
        at org.bukkit.craftbukkit.v1_6_R2.CraftServer.reload(CraftServer.java:57
5)
        at org.bukkit.Bukkit.reload(Bukkit.java:275)
        at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:
23)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:18
9)
        at org.bukkit.craftbukkit.v1_6_R2.CraftServer.dispatchCommand(CraftServe
r.java:523)
        at net.minecraft.server.v1_6_R2.PlayerConnection.handleCommand(PlayerCon
nection.java:964)
        at net.minecraft.server.v1_6_R2.PlayerConnection.chat(PlayerConnection.j
ava:882)
        at net.minecraft.server.v1_6_R2.PlayerConnection.a(PlayerConnection.java
:839)
        at net.minecraft.server.v1_6_R2.Packet3Chat.handle(SourceFile:49)
        at net.minecraft.server.v1_6_R2.NetworkManager.b(NetworkManager.java:296
)
        at net.minecraft.server.v1_6_R2.PlayerConnection.e(PlayerConnection.java
:118)
        at net.minecraft.server.v1_6_R2.ServerConnection.b(SourceFile:37)
        at net.minecraft.server.v1_6_R2.DedicatedServerConnection.b(SourceFile:3
0)
        at net.minecraft.server.v1_6_R2.MinecraftServer.t(MinecraftServer.java:5
90)
        at net.minecraft.server.v1_6_R2.DedicatedServer.t(DedicatedServer.java:2
26)
        at net.minecraft.server.v1_6_R2.MinecraftServer.s(MinecraftServer.java:4
86)
        at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java
:419)
        at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:5
82)

Can anyone explain to me what causes this error, and how to fix it?

 

First of all, if you are trying to broadcast this

Code:

this.getLogger().info("Player " + p + " has been kicked.");

to the players on the server then you should make it this:

Code:

Bukkit.broadcastMessage("Player " + p + " has been kicked.");

 

Shzylo
See what happens when you store player objects on a list?

 

I think we're gonna need to see the rest of the code to help out

 

MayoDwarf I just use that to post in the console, I am going to be logging information there for when you reload the plugin or disable it, make sure no errors occur.

Here is my full code of my main class:

Code:java

package me.shzylo.extremepaintball;
 
import java.util.ArrayList;
 
import me.shzylo.extremepaintball.commands.CmdArena;
import me.shzylo.extremepaintball.commands.CmdWand;
import me.shzylo.extremepaintball.commands.JoinCommand;
import me.shzylo.extremepaintball.commands.LeaveCommand;
import me.shzylo.extremepaintball.events.BlockEvents;
import me.shzylo.extremepaintball.events.SignEvents;
import me.shzylo.extremepaintball.items.Bow;
import me.shzylo.extremepaintball.items.Shop;
import me.shzylo.extremepaintball.wand.Selector;
 
import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.plugin.PluginManager;
import org.bukkit.plugin.java.JavaPlugin;
 
public final class ExtremePaintball extends JavaPlugin {
    Selector selector;
 
    public final String EPB_MSG = ("[" + ChatColor.AQUA + "Extreme" + ChatColor.RED + "Paintball" + ChatColor.WHITE + "]");
    public final String ERR_NOT_PLAYER = EPB_MSG + ChatColor.RED + " You must be a player!";
    public final String EPB_JOIN_MSG = EPB_MSG + ChatColor.GOLD + " You have joined the game!";
    public final String EPB_LEAVE_MSG = EPB_MSG + ChatColor.GOLD + " You have left the game!";
 
    public ArrayList<Player> playing = new ArrayList<Player>();
    public ArrayList<Player> redTeam = new ArrayList<Player>();
    public ArrayList<Player> blueTeam = new ArrayList<Player>();
 
    public void onEnable() {
        this.saveDefaultConfig();
        selector = new Selector(this, getConfig().getInt("wand-tool"));
        initCommands();
        initListeners();
    }
 
    public void onDisable() {
        kick();
        this.getLogger().info("No players are in-game. Disabled");
    }
 
    public boolean onCommand(CommandSender sender, Command command, String lbl, String[] args) {
        String cmd = command.getName();
 
        if (cmd.equalsIgnoreCase("epb")) {
            if (args.length == 0) {
                sender.sendMessage("[]----------" + EPB_MSG + "----------[]");
                sender.sendMessage(ChatColor.GREEN + "Version: " + ChatColor.GOLD + this.getDescription().getVersion());
                sender.sendMessage(ChatColor.GREEN + "Idea By: " + ChatColor.GOLD + "theunknownmana");
                sender.sendMessage(ChatColor.GREEN + "Code By: " + ChatColor.GOLD + "Shzylo");
                sender.sendMessage("");
                sender.sendMessage("----[" + ChatColor.AQUA + "Commands" + ChatColor.WHITE + "]----");
                sender.sendMessage(ChatColor.GREEN + "/epbjoin" + ChatColor.GOLD + " Join the lobby");
                sender.sendMessage(ChatColor.GREEN + "/epbleave" + ChatColor.GOLD + " Leave the lobby");
                return true;
            } else if (args.length > 0) {
                if (args.length == 1) {
                    if (args[0].equalsIgnoreCase("reload") || args[0].equalsIgnoreCase("rl")) {
                        this.reloadConfig();
                        sender.sendMessage(ChatColor.BLUE + "ExtremePaintball has been reloaded!");
                        kick();
                    }
                } else if (args.length == 2) {
 
                }
            }
        }
        return false;
    }
 
    private void initCommands() {
        getCommand("epbwand").setExecutor(new CmdWand(this));
        getCommand("epbarena").setExecutor(new CmdArena(this, selector));
        getCommand("epbjoin").setExecutor(new JoinCommand(this));
        getCommand("epbleave").setExecutor(new LeaveCommand(this));
    }
 
    private void initListeners() {
        PluginManager pm = getServer().getPluginManager();
        pm.registerEvents(new BlockEvents(this), this);
        pm.registerEvents(new Bow(this), this);
        pm.registerEvents(new SignEvents(this), this);
        pm.registerEvents(new Shop(this), this);
    }
 
    private void kick() {
        if (!(playing.isEmpty())) {
            for
            (Player p
                    : // This was all separated to see where the error was.
                        playing /* ERROR OCCURS HERE */ ) {
                if (this.redTeam.contains(p))
                    this.redTeam.remove(p);
                if (this.blueTeam.contains(p))
                    this.blueTeam.remove(p);
 
                this.playing.remove(p);
                this.getLogger().info("Player " + p + " has been kicked.");
                p.sendMessage(ChatColor.RED + "You have been kicked from the game!");
            }
 
        }
    }
}

 

Hmm. Not sure. I'd rather add player Names to a list than the Player object itself. Don't know if that'd make things better...

 

I have not ever thought about taking a player's name. If I were to do that, how would I get the player? Ex:

for (String playerName : myList) {
// send a message to them.
}

 

Code:java

Player player = getServer().getPlayer(playerName);

 

WauloK I tried using strings instead, I get the same error at the same location.

 

Shzylo
This error is occurring because you can't remove elements from a list at the same time you are iterating through it! (ConcurrentModificationException! Look it up!!)

Code:

for (Player p : playing) {
            if (this.redTeam.contains(p))
                this.redTeam.remove(p);
            if (this.blueTeam.contains(p))
                this.blueTeam.remove(p);
 
            this.playing.remove(p);
            this.getLogger().info("Player " + p + " has been kicked.");
            p.sendMessage(ChatColor.RED + "You have been kicked from the game!");
        }

Instead.. do something like:

Code:

List<Player> toRemove = new ArrayList<Player>();
List<Player> blueToRemove = new ArrayList<Player>();
List<Player> redToRemove = new ArrayList<Player>();
for (Player p : playing) {
            if (this.redTeam.contains(p))
                redToRemove.add(p);
                //this.redTeam.remove(p);
            if (this.blueTeam.contains(p))
                blueToRemove.add(p);
                //this.blueTeam.remove(p);
            toRemove.add(p);
            //this.playing.remove(p);
            this.getLogger().info("Player " + p + " has been kicked.");
            p.sendMessage(ChatColor.RED + "You have been kicked from the game!");
        }
for(Player p:blueToRemove){
  this.blueTeam.remove(p);
}
for(Player p:redToRemove){
  this.redTeam.remove(p);
}
for(Player p:toRemove){
  this.playing.remove(p);
}