ArrayList is backed by array and LinkedList backed Node's linked with refernece.
So operation on ArrayList is actaully evalute operation on array. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation.
and on LinkedList all of the operations perform as could be expected for a doubly-linked list. Operations that index into the list will traverse the list from the beginning or the end, whichever is closer to the specified index.
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