The answer is that no standard Java Collections class fulfills all requirements, so a custom data structure is needed. This is correct because while TreeSet provides O(log n) insertion and removal, it lacks indexed access entirely, and while ArrayList offers O(1) indexed access, it requires O(n log n) sorting after each insertion, failing the O(log n) requirement. The technical concept at play is that achieving O(log n) sorted indexed access demands an order statistic tree—a balanced binary search tree augmented with subtree sizes—which is not part of the standard Java Collections Framework. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your deep understanding of the trade-offs between TreeSet, ArrayList, and PriorityQueue, and the common trap is assuming a standard class like TreeSet can be coerced into providing indexed access. Remember the mnemonic: “No standard set gives you index yet; for log-n rank, custom you must plan.”
1Z0-829 Working with Arrays and Collections Practice Question
This 1Z0-829 practice question tests your understanding of working with arrays and collections. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer is working on a high-performance trading application that processes market data. The system needs to maintain a sorted list of order IDs (Long values) that are frequently inserted and removed. The current implementation uses a TreeSet<Long> to store the order IDs. The application is experiencing performance degradation under high load, and profiling shows that the TreeSet operations are the bottleneck. The developer considers replacing the TreeSet with a data structure that offers O(log n) insertion and removal but also supports O(log n) indexed access (e.g., get by index) for batch processing. Which of the following should the developer choose to improve performance while maintaining the sorted order and adding indexed access?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
No standard Java Collections class fulfills all requirements; consider a custom implementation.
Option A is correct because no standard Java Collections class provides O(log n) insertion, removal, and O(log n) indexed access while maintaining sorted order. TreeSet offers O(log n) insertion/removal but lacks indexed access; ArrayList provides O(1) indexed access but requires O(n log n) sorting after each insertion; PriorityQueue offers O(log n) insertion/removal but only O(1) peek access, not indexed access. A custom data structure like an order statistic tree (e.g., a balanced binary search tree with subtree sizes) is needed to meet all requirements.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
No standard Java Collections class fulfills all requirements; consider a custom implementation.
Why this is correct
No built-in collection provides O(log n) insertion, removal, and indexed access simultaneously.
Related concept
Read the scenario before looking for a memorised answer.
✗
Replace with TreeMap<Long, Boolean> and use the key set for iteration and indexed access via keySet().toArray().
Why it's wrong here
TreeMap key set is sorted but indexed access via toArray() is O(n) each time.
✗
Replace with PriorityQueue<Long> and use poll() for removal and toArray() for indexed access.
Why it's wrong here
PriorityQueue does not maintain sorted order for iteration and does not support indexed access.
✗
Replace with ArrayList<Long> and use Collections.sort() after each insertion.
Why it's wrong here
Sorting after each insertion is O(n log n), worse than TreeSet O(log n).
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume TreeSet or TreeMap can provide indexed access via toArray() or keySet(), overlooking that those operations are O(n) and defeat the purpose of O(log n) performance requirements.
Detailed technical explanation
How to think about this question
An order statistic tree extends a balanced BST (e.g., Red-Black tree) by storing the size of the subtree at each node, enabling O(log n) selection of the k-th smallest element. Java's TreeSet is implemented as a Red-Black tree but does not expose subtree sizes, so indexed access would require an O(n) traversal. In high-frequency trading, where batch processing often requires retrieving orders by rank (e.g., top 10), the lack of O(log n) indexed access forces developers to implement a custom solution or use a library like ConcurrentSkipListSet with additional indexing logic.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 1Z0-829 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Working with Arrays and Collections — This question tests Working with Arrays and Collections — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: No standard Java Collections class fulfills all requirements; consider a custom implementation. — Option A is correct because no standard Java Collections class provides O(log n) insertion, removal, and O(log n) indexed access while maintaining sorted order. TreeSet offers O(log n) insertion/removal but lacks indexed access; ArrayList provides O(1) indexed access but requires O(n log n) sorting after each insertion; PriorityQueue offers O(log n) insertion/removal but only O(1) peek access, not indexed access. A custom data structure like an order statistic tree (e.g., a balanced binary search tree with subtree sizes) is needed to meet all requirements.
What should I do if I get this 1Z0-829 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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