1Z0-829 Working with Arrays and Collections Practice Question
A developer is implementing a cache that stores recent user sessions. The cache should maintain the most recently accessed session at the end, and when the cache reaches its maximum size (1000), it should remove the least recently accessed session (i.e., the oldest). The developer chooses a LinkedList to store sessions, adding new sessions at the end and removing from the front. However, performance is poor because searching for an existing session to update its position requires O(n) linear scan. Which collection should replace the LinkedList to improve performance while maintaining the removal order?
⚠ Common exam trap
Test-takers frequently choose HashSet for speed but forget that order is required, or choose TreeSet thinking sorted order helps, but neither maintains insertion/access order for LRU eviction.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
LinkedHashSet
LinkedHashSet (C) maintains insertion order (which can be used to represent access order if reinserted on access) and provides O(1) average-time complexity for add, remove, and contains operations. By removing and re-adding a session upon access, it moves to the end, and the oldest (first inserted) can be removed from the front when the size exceeds 1000, solving the O(n) scan problem of LinkedList.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
TreeSet
Why it's wrong here
Sorted order, not access order.
- ✗
HashSet
Why it's wrong here
No order guarantee.
- ✓
LinkedHashSet
Why this is correct
O(1) add, remove, contains; maintains insertion order; can reinsert to move to end.
- ✗
ArrayList
Why it's wrong here
Removal from front is O(n).
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