Java removing elements from List of maps

Question

I have Java ArrayList<Map<String, Object>>. Is it okay to remove elements from that list as follows:

    for (Map<String, Object> anObject : manyObjects) {
        if (anObject.get("x").equals("y")) {
            manyObjects.remove(anObject);
        }
    }

Is there anything fundamentally wrong with this approach?

don't see any issues. Are you experiencing any problems or just looking for maybe a better way to accomplish your goals? — GregH, Jun 04 '15 at 21:35
See http://stackoverflow.com/questions/12583770/remove-value-from-list-of-map-in-java — Emiliano Sangoi, Jun 04 '15 at 21:38

aioobe · Answer 1 · 2015-06-04T21:41:19.377

No, you can't make structural modifications to the list (such as removing elements from it) while iterating over it using an enhanced for loop. That would (most likely) end up in a ConcurrentModificationException.

Here's a better way using the stream API:

manyObjects.removeIf(map -> map.get("x").equals("y"));

The "old" (pre Java 8) way is to use an iterator and the remove() method as follows:

Iterator<Map<String, Object>> iter = manyObjects.iterator();
while (iter.hasNext()) {
    if (iter.next().get("x").equals("y"))
        iter.remove();
}

score 1 · Accepted Answer · answered Jun 04 '15 at 21:35

You can't removes elements from a List while iterating over it with the enhanced for loop, since it will throw a CuncurrentModificationException. You can use an explicit iterator instead :

Iterator<Map<String, Object>> iter = manyObjects.iterator();
while (iter.hasNext()) {
    Map<String, Object> anObject = iter.next();
    if (anObject.get("x").equals("y")) {
        iter.remove();
    }
}

Java removing elements from List of maps

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