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Remove operation on iterator not allowed in CopyOnWriteArrayLIst
The 2019 Stack Overflow Developer Survey Results Are InHow do I efficiently iterate over each entry in a Java Map?Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loopWhy doesn't java.util.Set have get(int index)?Iterate through a HashMapWhy don't Java's +=, -=, *=, /= compound assignment operators require casting?Ways to iterate over a list in JavaWhy is executing Java code in comments with certain Unicode characters allowed?Merging list concurrently - Which is better, CopyOnWriteArrayList or ConcurrentLinkedQueue?Difference between Iterator,List iterator and CopyOnWriteArrayListUnsupportedOperationException while iterating over CopyOnWriteArrayList
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I am a beginner in Collections framework and came across this concept in CopyOnWriteArrayList:
the remove() operation on the returned Iterator is not permitted – resulting with UnsupportedOperationException. However the remove() method of the CopyOnWriteArrayList itself is permitted.
I am aware that for each mutation a copy of the underlying list is created but I am not sure why the above scenario is not permitted.Can anyone explain the reason why is this so?
java collections
asked Mar 22 at 2:48
ghostriderghostrider
4511517
add a comment |
I am a beginner in Collections framework and came across this concept in CopyOnWriteArrayList:
the remove() operation on the returned Iterator is not permitted – resulting with UnsupportedOperationException. However the remove() method of the CopyOnWriteArrayList itself is permitted.
I am aware that for each mutation a copy of the underlying list is created but I am not sure why the above scenario is not permitted.Can anyone explain the reason why is this so?
java collections
asked Mar 22 at 2:48
ghostriderghostrider
4511517
When you create a new iterator, the current copy is used. Modifying that copy will possibly change other iterators that work on the same copy.
– Johannes Kuhn
Mar 22 at 3:07
Wont the same thing happen using the list's own remove method as well?
– ghostrider
Mar 22 at 3:23
1
That is true but List and Iterators are different objects. The list is under no obligation to make sure iterator is consistent while iterator has to make sure it is consistent. If you call remove on the list while the iterator is ongoing, you run the risk of some strange behavior there as well but you are supposed to take care of that.
– Vinay Avasthi
Mar 22 at 3:56
The CopyOnWriteArrayList will take care that the iterator is not affected by it.
– Johannes Kuhn
Mar 22 at 4:22
add a comment |
I am a beginner in Collections framework and came across this concept in CopyOnWriteArrayList:
the remove() operation on the returned Iterator is not permitted – resulting with UnsupportedOperationException. However the remove() method of the CopyOnWriteArrayList itself is permitted.
I am aware that for each mutation a copy of the underlying list is created but I am not sure why the above scenario is not permitted.Can anyone explain the reason why is this so?
java collections
asked Mar 22 at 2:48
ghostriderghostrider
4511517
I am a beginner in Collections framework and came across this concept in CopyOnWriteArrayList:
the remove() operation on the returned Iterator is not permitted – resulting with UnsupportedOperationException. However the remove() method of the CopyOnWriteArrayList itself is permitted.
I am aware that for each mutation a copy of the underlying list is created but I am not sure why the above scenario is not permitted.Can anyone explain the reason why is this so?
java collections
java collections
asked Mar 22 at 2:48
ghostriderghostrider
4511517
asked Mar 22 at 2:48
ghostriderghostrider
4511517
asked Mar 22 at 2:48
ghostriderghostrider
4511517
asked Mar 22 at 2:48
ghostriderghostrider
4511517
asked Mar 22 at 2:48
ghostriderghostrider
4511517
4511517
When you create a new iterator, the current copy is used. Modifying that copy will possibly change other iterators that work on the same copy.
– Johannes Kuhn
Mar 22 at 3:07
Wont the same thing happen using the list's own remove method as well?
– ghostrider
Mar 22 at 3:23
1
That is true but List and Iterators are different objects. The list is under no obligation to make sure iterator is consistent while iterator has to make sure it is consistent. If you call remove on the list while the iterator is ongoing, you run the risk of some strange behavior there as well but you are supposed to take care of that.
– Vinay Avasthi
Mar 22 at 3:56
The CopyOnWriteArrayList will take care that the iterator is not affected by it.
– Johannes Kuhn
Mar 22 at 4:22
add a comment |
When you create a new iterator, the current copy is used. Modifying that copy will possibly change other iterators that work on the same copy.
– Johannes Kuhn
Mar 22 at 3:07
Wont the same thing happen using the list's own remove method as well?
– ghostrider
Mar 22 at 3:23
1
That is true but List and Iterators are different objects. The list is under no obligation to make sure iterator is consistent while iterator has to make sure it is consistent. If you call remove on the list while the iterator is ongoing, you run the risk of some strange behavior there as well but you are supposed to take care of that.
– Vinay Avasthi
Mar 22 at 3:56
The CopyOnWriteArrayList will take care that the iterator is not affected by it.
– Johannes Kuhn
Mar 22 at 4:22
When you create a new iterator, the current copy is used. Modifying that copy will possibly change other iterators that work on the same copy.
– Johannes Kuhn
Mar 22 at 3:07
When you create a new iterator, the current copy is used. Modifying that copy will possibly change other iterators that work on the same copy.
– Johannes Kuhn
Mar 22 at 3:07
Wont the same thing happen using the list's own remove method as well?
– ghostrider
Mar 22 at 3:23
Wont the same thing happen using the list's own remove method as well?
– ghostrider
Mar 22 at 3:23
1
1
That is true but List and Iterators are different objects. The list is under no obligation to make sure iterator is consistent while iterator has to make sure it is consistent. If you call remove on the list while the iterator is ongoing, you run the risk of some strange behavior there as well but you are supposed to take care of that.
– Vinay Avasthi
Mar 22 at 3:56
That is true but List and Iterators are different objects. The list is under no obligation to make sure iterator is consistent while iterator has to make sure it is consistent. If you call remove on the list while the iterator is ongoing, you run the risk of some strange behavior there as well but you are supposed to take care of that.
– Vinay Avasthi
Mar 22 at 3:56
The CopyOnWriteArrayList will take care that the iterator is not affected by it.
– Johannes Kuhn
Mar 22 at 4:22
The CopyOnWriteArrayList will take care that the iterator is not affected by it.
– Johannes Kuhn
Mar 22 at 4:22
add a comment |
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When you create a new iterator, the current copy is used. Modifying that copy will possibly change other iterators that work on the same copy.
– Johannes Kuhn
Mar 22 at 3:07
Wont the same thing happen using the list's own remove method as well?
– ghostrider
Mar 22 at 3:23
1
That is true but List and Iterators are different objects. The list is under no obligation to make sure iterator is consistent while iterator has to make sure it is consistent. If you call remove on the list while the iterator is ongoing, you run the risk of some strange behavior there as well but you are supposed to take care of that.
– Vinay Avasthi
Mar 22 at 3:56
The CopyOnWriteArrayList will take care that the iterator is not affected by it.
– Johannes Kuhn
Mar 22 at 4:22