What is the difference between ArrayList and LinkedList?

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Accepted Answer

Both implement List but use different internal structures. ArrayList — backed by a dynamic array . O(1) random access via index; O(n) insert/delete in the middle. Best for read-heavy workloads. LinkedList — doubly-linked list of nodes. O(1) insert/remove at head/tail (given a reference); O(n) indexed access. Higher per-element memory due to next/prev pointers. Implements Deque . Rule — default to ArrayList ; use LinkedList (or ArrayDeque ) only when you need queue/deque semantics. ArrayList wins in practice for almost all cases due to cache locality. Know the O(1) vs O(n) trade-offs for each operation. The practical recommendation to prefer ArrayList shows real-world experience over theoretical knowledge.