What is the difference between Array and ArrayList?

Expert Posts
,
1

In Java, both Array and ArrayList are used to store collections of elements, but they have distinct characteristics and use cases.

Key Differences

  1. Size Flexibility:
  2. Array: Has a fixed size. Once an array is created, its size cannot be changed.
  3. ArrayList: Is dynamic in size. It automatically resizes itself when elements are added or removed.
  4. Type of Elements:
  5. Array: Can store both primitive types (e.g., int, char) and objects.
  6. ArrayList: Can only store objects. For primitive types, you must use their wrapper classes (e.g., Integer, Character).
  7. Performance:
  8. Array: Generally faster for fixed-size collections since it doesn't involve overhead from resizing.
  9. ArrayList: Slightly slower due to dynamic resizing, but it offers more flexibility.
  10. Memory Usage:
  11. Array: More memory-efficient for large fixed-size collections because it doesn't have the overhead associated with dynamic resizing.
  12. ArrayList: Uses more memory because it maintains extra space for dynamic resizing and storage of objects.
  13. Built-in Methods:
  14. Array: Does not have built-in methods for common operations like adding, removing, or searching elements. You have to manage these manually.
  15. ArrayList: Provides a variety of methods like add(), remove(), contains(), size(), etc., making it easier to work with.
  16. Iteration:
  17. Array: Supports iteration using loops like for and foreach.
  18. ArrayList: Supports iteration using loops and provides Iterator and ListIterator for more advanced traversal.
  19. Usage:
  20. Array: Best used when the number of elements is known in advance and the size does not need to change.
  21. ArrayList: Best used when the number of elements may vary, and you need the flexibility of dynamic resizing.

Summary

  • Array:
  • Fixed size.
  • Can store primitives and objects.
  • Manual management of operations.
  • More memory-efficient for large, fixed collections.
  • ArrayList:
  • Dynamic size.
  • Stores only objects.
  • Built-in methods for easy management.
  • More flexible but with a slight overhead.

Follow-up Question

  1. When would you prefer using an Array over an ArrayList?
  2. Answer: Use an Array when the size of the collection is fixed and known in advance, and when performance and memory efficiency are critical.