Removing items from a collection in java while iterating over it

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Normally when you remove an element from a collection while looping over the collection, you’ll get a Concurrent Modification Exception. This is partially why the Iterator interface has a remove() method. Using an iterator is the only safe way to modify a collection of elements while traversing them.

The code would go something like this:

Set<SomeClass> set = new HashSet<SomeClass>();
fillSet(set);
Iterator<SomeClass> setIterator = set.iterator();
while (setIterator.hasNext()) {
    SomeClass currentElement = setIterator.next();
    if (setOfElementsToRemove(currentElement).size() > 0) {
        setIterator.remove();
    }
}

This way you’ll safely remove all elements that generate a removal set from your setOfElementsToRemove().

EDIT

Based on a comment to another answer, this may be more what you want:

Set<SomeClass> set = new HashSet<SomeClass>();
Set<SomeClass> removalSet = new HashSet<SomeClass>();
fillSet(set);

for (SomeClass currentElement : set) {
    removalSet.addAll(setOfElementsToRemove(currentElement);
}

set.removeAll(removalSet);

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