This content originally appeared on DEV Community and was authored by Tamilselvan K
When working with data structures in Java, two of the most commonly used classes are ArrayList and LinkedList. Both are part of the java.util package and implement the List interface, which means they share many common methods. However, the way they work internally is different, and this difference makes each one suitable for different use cases.
ArrayList
Based on Dynamic Array
ArrayList internally uses a dynamic array to store elements.Fast Access (O(1))
Accessing (reading) an element using an index is very fast because it directly uses the array index.Slow Insertion/Deletion
Insertion or deletion in the middle of the list is slow because elements have to be shifted to maintain order.Memory Usage
Takes less memory because it stores only the data (array of elements).Best Use Case
Ideal when searching and accessing elements is frequent.
LinkedList
Based on Doubly Linked Nodes
LinkedList internally uses doubly linked nodes where each node stores the data and references (links) to the next and previous nodes.Slow Access (O(n))
Accessing elements is slower because you have to traverse nodes one by one until you reach the required index.Fast Insertion/Deletion
Insertion and deletion are faster (especially in the middle of the list) because only the links are updated – no shifting of elements is required.Memory Usage
Consumes more memory as each node stores data + reference to next + reference to previous.Best Use Case
Ideal when insertion and deletion are frequent.
Side-by-Side Comparison
| Feature | ArrayList (Dynamic Array) | LinkedList (Doubly Linked List) |
|---|---|---|
| Storage | Dynamic Array | Doubly Linked Nodes |
| Access (Read) | Fast – O(1) | Slow – O(n) |
| Insertion/Deletion | Slow (shifting needed) | Fast (update node links) |
| Memory | Less (stores only data) | More (data + next + previous references) |
| Best For | Searching & frequent access | Frequent insertions & deletions |
Special LinkedList Methods
Apart from the common List methods, LinkedList provides some additional methods:
-
addFirst()– Add element at the beginning -
addLast()– Add element at the end -
getFirst()– Retrieve first element -
getLast()– Retrieve last element -
removeFirst()– Remove first element -
removeLast()– Remove last element
This content originally appeared on DEV Community and was authored by Tamilselvan K