java.util.ConcurrentModificationException in For loop

Question

I am trying to program an IM software, I want to let user leave the conversation and tell his partner that he has left... I prefer to use for loop instead Iterator, seek all the users and get the user who ask to leave and remove him... like that:

   for(Clientuser Cu: EIQserver.OnlineusersList)
          if(Cu.ID.equals(thsisUser.ID)) // find the user who ask to leave 
          {
          Omsg.setBody("@@!&$$$$@@@####$$$$"); //code means : clien! ur parter leaves...
                 sendMessage(Omsg); // sed message to thje partner with that code
                 EIQserver.OnlineusersList.remove(Cu);// remove the partner
                EIQserver.COUNTER--;// decrease counter.

          }

I get Exception: java.util.ConcurrentModificationException

I was using iterators, and to get rid of this exception, I convert to for, but the same exception still appears!! how may I get rid of this exception?

Answer 1

Faulting line: EIQserver.OnlineusersList.remove(Cu);

You can only remove elements from a collection that is being iterated over via the Iterator object you are using to iterate.

for (Iterator<Clientuser> it = EIQserver.OnlineusersList.iterator(); it.hasNext();)
{
    Clientuser cu = it.next();
    if (!cu.ID.equals(thsisUser.ID))
        continue;
    // other code
    it.remove();
}