HashSet.remove() and Iterator.remove() not working

Asked 2008-10-31T18:25:44.923

I'm having problems with Iterator.remove() called on a HashSet.

I've a Set of time stamped objects. Before adding a new item to the Set, I loop through the set, identify an old version of that data object and remove it (before adding the new object). the timestamp is included in hashCode and equals(), but not equalsData().

for (Iterator<DataResult> i = allResults.iterator(); i.hasNext();)
{
    DataResult oldData = i.next();
    if (data.equalsData(oldData))
    {   
        i.remove();
        break;
    }
}
allResults.add(data)

The odd thing is that i.remove() silently fails (no exception) for some of the items in the set. I've verified

The line i.remove() is actually called. I can call it from the debugger directly at the breakpoint in Eclipse and it still fails to change the state of Set
DataResult is an immutable object so it can't have changed after being added to the set originally.
The equals and hashCode() methods use @Override to ensure they are the correct methods. Unit tests verify these work.
This also fails if I just use a for statement and Set.remove instead. (e.g. loop through the items, find the item in the list, then call Set.remove(oldData) after the loop).
I've tested in JDK 5 and JDK 6.

I thought I must be missing something basic, but after spending some significant time on this my colleague and I are stumped. Any suggestions for things to check?

EDIT:

There have been questions - is DataResult truly immutable. Yes. There are no setters. And when the Date object is retrieved (which is a mutable object), it is done by creating a copy.

public Date getEntryTime()
{
    return DateUtil.copyDate(entryTime);
}

public static Date copyDate(Date date)
{
    return (date == null) ? null : new Date(date.getTime());
}

FURTHER EDIT (some time later)

java collections

Edit Report

2 Answers

Under the covers, HashSet uses HashMap, which calls HashMap.removeEntryForKey(Object) when either HashSet.remove(Object) or Iterator.remove() is called. This method uses both hashCode() and equals() to validate that it is removing the proper object from the collection.

If both Iterator.remove() and HashSet.remove(Object) are not working, then something is definitely wrong with your equals() or hashCode() methods. Posting the code for these would be helpful in diagnosis of your issue.

answered 2008-11-01T05:01:56.527

Have you tried something like

boolean removed = allResults.remove(oldData)
if (!removed) // COMPLAIN BITTERLY!

In other words, remove the object from the Set and break the loop. That won't cause the Iterator to complain. I don't think this is a long term solution but would probably give you some information about the hashCode, equals and equalsData methods

answered 2008-10-31T18:40:22.833

HashSet.remove() and Iterator.remove() not working

2 Answers

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