1. Underlying Data Structure

  • ArrayList: Based on a dynamic array. It uses a resizable array to store elements.
  • LinkedList: Based on a doubly linked list. Each element (node) contains a reference to the previous and next nodes.

2. Access Time (Random Access)

  • ArrayList: Provides O(1) time complexity for accessing elements using their index.
  • LinkedList: Provides O(n) time complexity for accessing elements, as traversal is required.

3. Insertion and Deletion

  • ArrayList:
    • Add at the end: O(1) (amortized).
    • Add/remove at an arbitrary position: O(n) (due to shifting).
  • LinkedList:
    • Add/remove at the beginning or end: O(1).
    • Add/remove at an arbitrary position: O(n) (due to traversal).

4. Memory Usage

  • ArrayList: Requires less memory since elements are stored contiguously.
  • LinkedList: Requires more memory due to additional pointers (next and previous references).

5. Iteration Performance

  • ArrayList: Faster iteration due to better cache locality.
  • LinkedList: Slower iteration due to scattered memory allocation.

6. Use Case

  • ArrayList:
    • Frequent random access is needed.
    • Insertions and deletions are infrequent.
  • LinkedList:
    • Frequent insertions and deletions are required.
    • Sequential access is common.

7. Thread-Safety

  • Both are not thread-safe.
  • Use Collections.synchronizedList() or CopyOnWriteArrayList for thread-safe operations.

Summary Table

Feature ArrayList LinkedList
Data Structure Dynamic Array Doubly Linked List
Access Time O(1) (random access) O(n) (traversal required)
Insertion/Deletion O(n) (shifting elements) O(1) (with node references)
Memory Overhead Less More (due to pointers)
Iteration Performance Faster Slower
Best Use Case Frequent random access Frequent insertions/deletions