1Z0-811 Java Basics and Syntax Practice Question
You are writing a program that processes a list of transactions. Each transaction has a timestamp (long), amount (double), and type (String). The program needs to iterate through the transactions in the order they were added. Which collection should you use to maintain insertion order and allow fast iteration?
⚠ Common exam trap
Oracle often tests the misconception that LinkedList is the best choice for insertion-order preservation and iteration, but ArrayList is actually faster for iteration due to contiguous memory and lower overhead, while LinkedList is better for frequent insertions/removals at the beginning or middle.
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
✓
ArrayList<Transaction>
ArrayList maintains insertion order and provides O(1) random access and fast iteration via index-based traversal. It is the correct choice when you need to preserve the order in which elements were added and iterate over them sequentially without requiring sorting or unique constraints.
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<Transaction>
Why it's wrong here
Sorted order, not insertion order.
- ✗
LinkedList<Transaction>
Why it's wrong here
Maintains order but slower iteration for large lists.
- ✗
HashSet<Transaction>
Why it's wrong here
No order guarantee.
- ✓
ArrayList<Transaction>
Why this is correct
Maintains insertion order, fast iteration.
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