Solved Getting top 10 kills

I'm making a plugin that keeps track of players kills, deaths etc. There are leaderboards with top kills and such. The simplest way is going through the config and checking. But let's imagine a server has had like 5k unique players. Then going through the config takes a stupid amount of time and lags the server. (It also has to be done everytime someone opens the leaderboard GUI). In order to recude I/O calls I made it so that when a server starts it copies all the data from the config into several HashMap which contain player's UUID and their kills/deaths etc. Whenever the data is changed the hashmap get's sorted with a function I made here:

Code:

public void sortKills()
    {
        HashMap<String, Integer> unordered = new HashMap<String, Integer>();
        HashMap<String, Integer> ordered = new HashMap<String, Integer>();

        unordered.putAll(kills);
    
        String playername;
        int highestvalue = 0;
        for (int i = 0; i < unordered.size(); i++)
        {
            for (Entry<String, Integer> e : unordered.entrySet())
            {
                if (e.getValue() > highestvalue)
                {
                    highestvalue = e.getValue();
                    playername = e.getKey();
                    ordered.put(playername, highestvalue);
                    unordered.remove(playername);
                }
            }
        }
    
        kills.clear();
        kills.putAll(ordered);
    }

My problem is that sorting the data when the data changes is that it causes:

Code:

java.util.ConcurrentModificationException

Is there any way to work around this?

EDIT
if it matters the error happens at:

Code:

for (Entry<String, Integer> e : unordered.entrySet())

Any answers are appreciated.

Issue solved.

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

ConcurrentModificationException is called when you edit a sequence at the same time you iterate through it. For example, the following code would cause a Concurrent Modification Exception:

Code:

List<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("c");
for (String s : list) list.remove(s);

To fix it, you could change the line to

Code:

for (String s : list.toArray(new String[list.size()])) list.remove(s);

or anything that makes a duplicate list to iterate through

As for efficiency in getting the leaderboards, you should have them only periodically update (maybe every 10 minutes), and use a sorting algorithm run over an asynchronous bukkit runnable. That way, when a player looks at the leaderboards, it just shows them the pre-calculated values for 1st place, 2nd place, etc.

 

Just to add on (this will already work); but you could also create an empty array:

Code:Java

list.toArray(new String[0])

 

Thank you for the responses! I solved this issue by just sorting the list when the data changes. I forgot to make an async schedule call so thanks for that!