Question 28 of 509

Working with Arrays and Collections →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to use a ConcurrentLinkedDeque for writes and have consumers obtain a consistent snapshot by calling toArray(). This approach is correct because ConcurrentLinkedDeque provides lock-free, non-blocking writes that minimize latency for the producer thread, while toArray() delivers a point-in-time, immutable snapshot of the deque without blocking concurrent modifications, ensuring consumers see a consistent view. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of concurrent collections and the trade-off between low-latency writes and consistent iteration—a common trap is assuming that synchronized collections or iterators are safe under concurrent modification, but they cause blocking and stale snapshots. Remember the key mnemonic: "Deque for writes, toArray for reads"—the snapshot is O(n) but lock-free, making it ideal for high-frequency trading scenarios where producer throughput is critical.

1Z0-829 Working with Arrays and Collections Practice Question

This 1Z0-829 practice question tests your understanding of working with arrays and collections. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.

You are developing a high-frequency trading application that processes a stream of market data ticks. Each tick is an immutable object containing timestamp, price, and volume. The ticks arrive in real time and must be stored in a collection for later analysis. The collection is accessed by multiple threads: one producer thread adds ticks, and multiple consumer threads periodically iterate to compute moving averages. The system must minimize latency for the producer and ensure that consumers see a consistent snapshot of data without interfering with ongoing writes. You initially used a synchronized ArrayList, but profiler results show high contention and poor throughput. You consider the following approaches. Which one best addresses the requirements?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.

Question 1hardmultiple choice

Full question →

A
Replace ArrayList with CopyOnWriteArrayList, which provides thread-safety without explicit synchronization and allows concurrent iteration while modifications occur.
Why wrong: CopyOnWriteArrayList creates a new copy on every write, causing O(n) cost per insertion. In a high-frequency trading scenario with many writes, this leads to excessive memory allocation and latency, making it unsuitable for the producer.
B
Use a ConcurrentLinkedDeque for writes and have consumers obtain a consistent snapshot by calling toArray() on the deque. The toArray() operation is O(n) but provides a point-in-time view without blocking the producer.
ConcurrentLinkedDeque offers lock-free, low-latency writes for the producer. Calling toArray() creates a snapshot that is consistent as of the moment of the call, allowing consumers to iterate without interference. The O(n) cost of toArray() is acceptable if consumers iterate infrequently relative to the number of writes.
C
Use a ConcurrentLinkedDeque and have consumers acquire a read lock when iterating, while the producer uses a write lock. This provides fine-grained locking and reduces contention.
Why wrong: ConcurrentLinkedDeque is non-blocking and does not support explicit locks. Attempting to acquire locks on it would cause compilation errors or misuse. Additionally, it does not provide consistent snapshots because its iterator is weakly consistent.
D
Maintain two synchronized ArrayLists. The producer writes to one list while consumers read from the other. Periodically, swap references using an AtomicReference. This allows lock-free reads after the swap.
Why wrong: This double-buffering approach requires careful coordination to ensure that consumers do not read a partially updated list. The swap itself is atomic, but if the producer is writing to the 'active' list while consumers read the 'snapshot' list, the snapshot becomes stale. This design does not provide real-time access to the latest data and may miss ticks.

Full breakdown with real-world context →

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

✓

Use a ConcurrentLinkedDeque for writes and have consumers obtain a consistent snapshot by calling toArray() on the deque. The toArray() operation is O(n) but provides a point-in-time view without blocking the producer.

Option B is correct because ConcurrentLinkedDeque allows lock-free, non-blocking writes (ideal for low-latency producers) and calling toArray() provides a consistent, immutable snapshot of the deque at that instant without blocking concurrent modifications. This satisfies the requirement for multiple consumers to see a consistent view while the producer continues writing with minimal latency.

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.

✗
Replace ArrayList with CopyOnWriteArrayList, which provides thread-safety without explicit synchronization and allows concurrent iteration while modifications occur.
Why it's wrong here
CopyOnWriteArrayList creates a new copy on every write, causing O(n) cost per insertion. In a high-frequency trading scenario with many writes, this leads to excessive memory allocation and latency, making it unsuitable for the producer.
✓
Use a ConcurrentLinkedDeque for writes and have consumers obtain a consistent snapshot by calling toArray() on the deque. The toArray() operation is O(n) but provides a point-in-time view without blocking the producer.
Why this is correct
ConcurrentLinkedDeque offers lock-free, low-latency writes for the producer. Calling toArray() creates a snapshot that is consistent as of the moment of the call, allowing consumers to iterate without interference. The O(n) cost of toArray() is acceptable if consumers iterate infrequently relative to the number of writes.
Clue confirmation
The clue words "best", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a ConcurrentLinkedDeque and have consumers acquire a read lock when iterating, while the producer uses a write lock. This provides fine-grained locking and reduces contention.
Why it's wrong here
ConcurrentLinkedDeque is non-blocking and does not support explicit locks. Attempting to acquire locks on it would cause compilation errors or misuse. Additionally, it does not provide consistent snapshots because its iterator is weakly consistent.
✗
Maintain two synchronized ArrayLists. The producer writes to one list while consumers read from the other. Periodically, swap references using an AtomicReference. This allows lock-free reads after the swap.
Why it's wrong here
This double-buffering approach requires careful coordination to ensure that consumers do not read a partially updated list. The swap itself is atomic, but if the producer is writing to the 'active' list while consumers read the 'snapshot' list, the snapshot becomes stale. This design does not provide real-time access to the latest data and may miss ticks.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume CopyOnWriteArrayList is the best choice for concurrent reads and writes, but they overlook its write-cost penalty, which is disastrous for high-frequency producers; the correct solution uses a non-blocking collection with a snapshot mechanism.

Trap categories for this question

Scenario analysis trap
CopyOnWriteArrayList creates a new copy on every write, causing O(n) cost per insertion. In a high-frequency trading scenario with many writes, this leads to excessive memory allocation and latency, making it unsuitable for the producer.

Detailed technical explanation

How to think about this question

ConcurrentLinkedDeque is based on a non-blocking linked-list algorithm using CAS (Compare-And-Swap) operations, enabling thread-safe adds and removals without locks. The toArray() method creates a new array by traversing the deque at the moment of the call, providing a consistent snapshot that is safe for iteration even as other threads modify the deque concurrently. In real-world high-frequency trading, this pattern allows the producer to enqueue ticks with nanosecond-level latency while consumers compute moving averages on periodic snapshots without any blocking.

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.

Related 1Z0-829 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Handling Date, Time, Text, Numeric and Boolean Values practice questions

Practise 1Z0-829 questions linked to Handling Date, Time, Text, Numeric and Boolean Values.

Controlling Program Flow practice questions

Practise 1Z0-829 questions linked to Controlling Program Flow.

Utilizing Java Object-Oriented Approach practice questions

Practise 1Z0-829 questions linked to Utilizing Java Object-Oriented Approach.

Handling Exceptions practice questions

Practise 1Z0-829 questions linked to Handling Exceptions.

Working with Arrays and Collections practice questions

Practise 1Z0-829 questions linked to Working with Arrays and Collections.

Working with Streams and Lambda Expressions practice questions

Practise 1Z0-829 questions linked to Working with Streams and Lambda Expressions.

Java Platform Overview and Packaging practice questions

Practise 1Z0-829 questions linked to Java Platform Overview and Packaging.

Java I/O API and Securing Applications practice questions

Practise 1Z0-829 questions linked to Java I/O API and Securing Applications.

1Z0-829 fundamentals practice questions

Practise 1Z0-829 questions linked to 1Z0-829 fundamentals.

1Z0-829 scenario practice questions

Practise 1Z0-829 questions linked to 1Z0-829 scenario.

1Z0-829 troubleshooting practice questions

Practise 1Z0-829 questions linked to 1Z0-829 troubleshooting.

Practice this exam

Start a free 1Z0-829 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

1Z0-829 practice-test guide →Study guide →Browse all practice tests

FAQ

Questions learners often ask

What does this 1Z0-829 question test?

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: Use a ConcurrentLinkedDeque for writes and have consumers obtain a consistent snapshot by calling toArray() on the deque. The toArray() operation is O(n) but provides a point-in-time view without blocking the producer. — Option B is correct because ConcurrentLinkedDeque allows lock-free, non-blocking writes (ideal for low-latency producers) and calling toArray() provides a consistent, immutable snapshot of the deque at that instant without blocking concurrent modifications. This satisfies the requirement for multiple consumers to see a consistent view while the producer continues writing with minimal latency.

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.

Are there clue words in this question I should notice?

Yes — watch for: "best", "minimum / minimize". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Last reviewed: Jun 25, 2026

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

This 1Z0-829 practice question is part of Courseiva's free Oracle certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 1Z0-829 exam.