What is CopyOnWriteArrayList, how it is different than ArrayList

CopyOnWriteArrayList is a thread-safe counterpart of ArrayList. All mutable operations like add and set are implement by using a copy of the underlying array. Write operation is slower when compared the ArrayList as it takes a snapshot of the instance and does the write. This is useful when the traversal of the collection need not be synchronized during traversal with the original instance and the traversal is larger in count than the updates. This provides a fail safe iterator as it does not throw exception when the underlying collection is modified. At the same time the iterator will not reflect the modifications done to the collection, it just shows the snapshot of state taken at the moment when the iterator is created.