Solved ConcurrentModificationException

When i attempt to remove my player from the arena it errors, giving me a ConcurrentModificationException. It works when i call this method from the onDisable method, but it throws the error when i attempt to call it from the onCommand.

StackTrace

Code:

[15:37:23 WARN]: java.util.ConcurrentModificationException
[15:37:23 WARN]:        at java.util.ArrayList$Itr.checkForComodification(Unknow
n Source)
[15:37:23 WARN]:        at java.util.ArrayList$Itr.next(Unknown Source)
[15:37:23 WARN]:        at me.connor.kitminigame.ArenaManager.endArena(ArenaMana
ger.java:172)
[15:37:23 WARN]:        at me.connor.kitminigame.commands.ForceEnd.onCommand(For
ceEnd.java:41)
[15:37:23 WARN]:        at me.connor.managers.CommandManager.onCommand(CommandMa
nager.java:61)
[15:37:23 WARN]:        at org.bukkit.command.PluginCommand.execute(PluginComman
d.java:44)
[15:37:23 WARN]:        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCo
mmandMap.java:180)
[15:37:23 WARN]:        at org.bukkit.craftbukkit.v1_7_R2.CraftServer.dispatchCo
mmand(CraftServer.java:719)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.PlayerConnection.handleC
ommand(PlayerConnection.java:984)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.PlayerConnection.a(Playe
rConnection.java:829)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.PacketPlayInChat.a(Packe
tPlayInChat.java:28)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.PacketPlayInChat.handle(
PacketPlayInChat.java:65)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.NetworkManager.a(Network
Manager.java:148)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.ServerConnection.c(Serve
rConnection.java:77)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.MinecraftServer.v(Minecr
aftServer.java:705)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.DedicatedServer.v(Dedica
tedServer.java:273)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.MinecraftServer.u(Minecr
aftServer.java:568)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.MinecraftServer.run(Mine
craftServer.java:474)
[15:37:23 WARN]:        at net.minecraft.server.v1_7_R2.ThreadServerApplication.
run(SourceFile:618)
>

End Arena Method

Code:java

 //A method for ending an Arena:
public void endArena(String arenaName) {
 
if (getArena(arenaName) != null) { //If the arena exsists
 
Arena arena = getArena(arenaName); //Create an arena for using in this method
 
//Send them a message
arena.sendMessage(ChatColor.GOLD + "The arena has ended :(");
 
//Set ingame
arena.setInGame(false);
 
for (String s: arena.getPlayers()) {//Loop through every player in the arena;
//Teleport them:
 
Player player = Bukkit.getPlayer(s); //Create a player by the name
player.teleport(arena.getLobbyLocation());
 
player.getInventory().clear(); //Clear the players inventory
player.setHealth(player.getMaxHealth()); //Heal the player
player.setFireTicks(0); //Heal the player even more ^ ^ ^
 
arena.sendMessage(arenaName);
//Remove them all from the list
removePlayer(player, arena.getName());
arena.sendMessage("test5");
}
}
}

Command

Code:java

public void onCommand(Player p, String[] args) {
if(!p.hasPermission("spleef.admin")) {
MessageManager.getInstance().severe(p, "You don't have permission to force end spleef arenas!");
return;
}
 
if(args == null) {
MessageManager.getInstance().severe(p, "You must specify a name for the arena!");
return;
}
 
if(args.length == 0) {
MessageManager.getInstance().severe(p, "Usage: /spleef forceEnd [name]");
return;
}
 
if(args.length > 1) {
MessageManager.getInstance().severe(p, "Arenas can only be 1 word!");
return;
}
 
//define a variable for the arena name
String arena = args[0];
 
//test if the arena already exists or not
if(!SettingsManager.getInstance().arenas.contains(arena)) {
MessageManager.getInstance().severe(p, "The arena " + ChatColor.AQUA + arena + ChatColor.RED + " does not exist!");//test to see if the arena already exists.
return;
}
 
ArenaManager.getManager().endArena(arena);//force end the arena
}

 

Code:

at me.connor.kitminigame.ArenaManager.endArena(ArenaMana
ger.java:172)

What's line 172 of ArenaManager?

 

MOMOTHEREAL

Sorry the end arena method line numbers don't line up. It is this part of that method.

Code:java

for (String s: arena.getPlayers()) {//Loop through every player in the arena;

 

cfil360
It's happening because you're trying to remove an element of a Collection from within the enhanced for loop. Consider using an iterator, and that should remedy the issue.

 

amhokies but why doesn't it throw the error from the onDisable method?

 

There's a possibility that it isn't looping when being called in the onDisable method. I don't know for sure, but I know it's what is causing the error.

 

amhokies I understand that, but how can it work in the onDisable, but not the command. Also how can i fix this, while still update the arena player list?

 

As I just said, I don't know why it is working in the disable. It's really hard to tell without being able to see console output, your code, etc. Use an iterator to iterate through the elements instead and the problem will be fixed.

 

amhokies Im confused as what u mean use an iterator. It is already iterating through the player list.

 

http://stackoverflow.com/questions/1196586/calling-remove-in-foreach-loop-in-java

 

amhokies Thanks

 

You might want to use getPlayerExact(String) instead of getPlayer(String)