- A
Use a sequential stream with a custom rate limiter (e.g., a semaphore) that blocks when the limit is reached.
A sequential stream combined with a rate limiter ensures requests are sent at a controlled pace, respecting the external service limits.
- B
Reduce the parallelism level by using a custom thread pool with a fixed number of threads.
Why wrong: This limits concurrency but does not provide fine-grained rate control; requests may still exceed the rate limit at peak times.
- C
Use filter to drop some sensor readings to reduce the load.
Why wrong: Dropping data is unacceptable as all readings need to be processed.
- D
Use a sequential stream and hope the processing completes within the time window.
Why wrong: Sequential stream might be safe but does not guarantee rate limiting; it could still send requests too quickly if the stream is large.
1Z0-829 Working with Streams and Lambda Expressions Practice Question
This 1Z0-829 practice question tests your understanding of working with streams and lambda expressions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 team is developing a real-time data processing pipeline that reads sensor data from a message queue. The pipeline uses a flatMap operation that calls an external geocoding service for each sensor reading. The external service has a rate limit of 10 requests per second and is slow (150ms average response time). The current code: sensorStream.parallelStream() .flatMap(reading -> getGeocode(reading).stream()) .forEach(system.out::println); The application is overloaded because parallel stream fires many concurrent requests, exceeding the rate limit and causing failures. They need to process all sensor data but must respect the rate limit. Which approach should they use?
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 sequential stream with a custom rate limiter (e.g., a semaphore) that blocks when the limit is reached.
Option A is correct because using a sequential stream with a custom rate limiter (e.g., a Semaphore configured to allow only 10 permits per second) ensures that the external geocoding service is called at a controlled rate, preventing rate-limit violations. The sequential stream processes elements one at a time, and the rate limiter blocks the thread when the limit is reached, naturally throttling requests to stay within the 10 requests/second limit while still processing all data.
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.
- ✓
Use a sequential stream with a custom rate limiter (e.g., a semaphore) that blocks when the limit is reached.
Why this is correct
A sequential stream combined with a rate limiter ensures requests are sent at a controlled pace, respecting the external service limits.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Reduce the parallelism level by using a custom thread pool with a fixed number of threads.
Why it's wrong here
This limits concurrency but does not provide fine-grained rate control; requests may still exceed the rate limit at peak times.
- ✗
Use filter to drop some sensor readings to reduce the load.
Why it's wrong here
Dropping data is unacceptable as all readings need to be processed.
- ✗
Use a sequential stream and hope the processing completes within the time window.
Why it's wrong here
Sequential stream might be safe but does not guarantee rate limiting; it could still send requests too quickly if the stream is large.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume that reducing parallelism (Option B) is sufficient to control request rates, but they overlook that even a small fixed thread pool can still exceed a low rate limit if requests are made too quickly, and that a rate limiter with temporal control is required to precisely throttle requests per second.
Detailed technical explanation
How to think about this question
Under the hood, a Semaphore with a timed permit acquisition (e.g., using tryAcquire with a timeout or a scheduled permit release) can be used to implement a token-bucket rate limiter, where permits are replenished at a fixed rate (e.g., 10 per second). This approach works with sequential streams because each element is processed one at a time, and the blocking call naturally paces the stream's throughput. In real-world scenarios, this pattern is common when integrating with external APIs that have strict rate limits, such as Google Maps Geocoding API or Twitter API, where exceeding the limit results in HTTP 429 responses.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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FAQ
Questions learners often ask
What does this 1Z0-829 question test?
Working with Streams and Lambda Expressions — This question tests Working with Streams and Lambda Expressions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a sequential stream with a custom rate limiter (e.g., a semaphore) that blocks when the limit is reached. — Option A is correct because using a sequential stream with a custom rate limiter (e.g., a Semaphore configured to allow only 10 permits per second) ensures that the external geocoding service is called at a controlled rate, preventing rate-limit violations. The sequential stream processes elements one at a time, and the rate limiter blocks the thread when the limit is reached, naturally throttling requests to stay within the 10 requests/second limit while still processing all data.
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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Last reviewed: Jul 4, 2026
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