Help needed on try/catch inside for loop

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1

I created my own exception class InvalidHallOfFameIDException. Basically what i’m doing is looping through a arraylist called hallOfFameMemberList that holds hall of fame members. Inside that loop i am looping through Hall Of Fames, which members can belong to. An exception(InvalidHallOfFameIDException) is thrown when a member’s id from hallOfFameMemberList does not equal to the Hall Of Fame’s id. The problem I am having is after the exception is thrown. After the exception is thrown I want to continue looping through hallOfFameMemberList. It goes to the next hofMember of hallOfFameMemberList then gives me this error:

java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
at java.util.AbstractList$Itr.next(Unknown Source)
at ReportWriter.displayReport3(HW6.java:1708)
at ReportWriter.DisplayReports(HW6.java:1478)
at HW6.main(HW6.java:399)

Here is my code


		/*loop to check and delete member from arraylist if member hall of fame id does not equal to hall of fame id*/
				for(HallOfFameMember hofMember: hallOfFameMemberList){
					
					memberFound = false;
					
					
					try{
						
						for(HallOfFame hof:hallOfFameArr){
						
						
								if(hofMember.GetHallOfFameId() == hof.GetHallOfFameId()){
							
                                                                     /*do something then set memberFound = true*/
							
								}
							
						}
					
						if(memberFound == false){
						

                                                        /*remove member from list*/
							hallOfFameMemberList.remove(hofMember);
							throw new InvalidHallOfFameIDException();
						}
					
					}catch(InvalidHallOfFameIDException e){
						

                                                hallOfFameMemberList.remove(hofMember);
						System.err.println("InvalidHallOfFameIDException was thrown:");
			                        System.err.println("HallOfFameMember " + hofMember.GetLastName() + ", " + hofMember.GetFirstName() + " with HOFId " + hofMember.GetHallOfFameId() + " was deleted");
						
						}

I don’t quite understand the error. Any ideas on what I can do?

2

java.util.ConcurrentModificationException
means you are modifying a collection (e.g. a List) while you are iterating over it.

In this case you’re iterating over “hallOfFameMemberList”, but you’re also trying to remove from it while you are still looping.

Instead I’d make a separate variable, e.g. validHallOfFameMemberList, and add all the good HallOfFameMembers there.

3

Jurn is right…you need to use an another list for storing valid members.

Also give a thought to BlockingQueues introduced in JDK5 and especially [URL=“http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/LinkedBlockingQueue.html”]LinkedBlockingQueue

4

Thanks for the reply guys!

I replaced the for(HallOfFameMember hofMember: hallOfFameMemberList) with a for loop to loop backwards so the next index being looped is never shifted. :slight_smile:

I appreciate you help.

5

Another valid solution is to use the standard for, which gives you an iterator to work with.

Via the iterator, even during iteration, you may remove elements.

Like so:


    // where myStuff [i]is a[/i] Collection
    for( Iterator<Stuff> i = myStuff.iterator(); i.hasNext(); ) {
        Stuff stuff = i.next();
        if( iDontWantThisStuff( stuff ) ) {
            i.remove();
        }
    }