Solved ConcurrentModificationException

I am getting a ConcurrentModificationException here:

Code:

                for (String s1 : serverPlayers.keySet()) {
                    for (String s2 : serverPlayers.get(s1).keySet()) {
                        try {
                            int op = Core.plugin.sqlManager.getOnlinePlayers(s1);
                            HashMap<String, Integer> gmPlayers = new HashMap<String, Integer>();
                            gmPlayers.put(s2, op);
                            serverPlayers.remove(s1);
                            serverPlayers.put(s1, gmPlayers);
                        } catch (SQLException e) {
                            e.printStackTrace();
                        } catch (ClassNotFoundException e) {
                            e.printStackTrace();
                        }
                    }
                }
                }

At this line exactly:

Code:

               for (String s1 : serverPlayers.keySet()) {

Does anyone know what causes this? Thanks for any help

 

@dlange you cant modify a collection while iterating over it

try creating a for loop that ends at the size of the collection

Code:

 for (int i = 0; i < {collection}.size; i++) {
                  object object = collection.get(0);
           }

 

@dlange Another thing you could do is make a copy of the collection, and iterate through the copy instead.

Code:

List<String> serverPlayersCopy = new ArrayList<>();
serverPlayersCopy.addAll(serverPlayers);
for (String s1 : serverPlayersCopy.keySet()) {
  for (String s2 : serverPlayersCopy.get(s1).keySet()) {
    try {
      int op = Core.plugin.sqlManager.getOnlinePlayers(s1);
      HashMap<String, Integer> gmPlayers = new HashMap<String, Integer>();
      gmPlayers.put(s2, op);
      serverPlayers.remove(s1);
      serverPlayers.put(s1, gmPlayers);
    } catch (SQLException e) {
      e.printStackTrace();
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    }
  }
}

That way you're not iterating through the collection that you're modifying.

 

@dlange Use an iterator insteads, you should be able to call Iterator#remove in it while iterating as long as the Collection is not unmodifiable.

 

Sweet thanks! I fixed it doing this:

Code:

                HashMap<String, HashMap<String, Integer>> serverPlayersCopy = (HashMap<String, HashMap<String, Integer>>) serverPlayers.clone();
                for (String s1 : serverPlayersCopy.keySet()) {
                    for (String s2 : serverPlayersCopy.get(s1).keySet()) {
                        try {
                            int op = Core.plugin.sqlManager.getOnlinePlayers(s1);
                            HashMap<String, Integer> gmPlayers = new HashMap<String, Integer>();
                            gmPlayers.put(s2, op);
                            serverPlayers.remove(s1);
                            serverPlayers.put(s1, gmPlayers);
                        } catch (SQLException e) {
                            e.printStackTrace();
                        } catch (ClassNotFoundException e) {
                            e.printStackTrace();
                        }
                    }
                }

 

Not the best of way to achieve this.

@Konato_K's suggestion was good.