- A
The pipeline will produce correct results if the stateful lambda is synchronized.
Why wrong: Synchronization can cause contention and degrade performance, but it may work; however, it is not a recommended approach and may still have ordering issues.
- B
The pipeline will produce non-deterministic results due to race conditions.
Stateful lambdas in parallel streams are discouraged because they introduce shared mutable state that leads to race conditions and unpredictable results.
- C
The pipeline will throw a ConcurrentModificationException.
Why wrong: ConcurrentModificationException occurs when the stream source is modified during iteration, not due to stateful lambda.
- D
The pipeline will always produce the same result regardless of parallelism.
Why wrong: Parallel stream processing with stateful lambda is inherently non-deterministic.
Quick Answer
The answer is non-deterministic results due to race conditions. This occurs because a stateful lambda in parallel streams mutates shared mutable state—such as a counter—without synchronization, and when multiple threads execute the map operation concurrently, they interfere with each other’s writes, leading to unpredictable outcomes. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this tests your understanding of the Stream API’s contract that intermediate operations like map must be stateless and non-interfering; the common trap is assuming that parallel execution automatically handles state safely. A reliable memory tip is “stateless for safety, stateful for chaos”—if your lambda modifies a shared variable, expect race conditions in parallel pipelines.
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. 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 team implements a stream pipeline that processes a large dataset in parallel. They use a stateful lambda expression inside the map operation to maintain a count. What is the most likely outcome?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
The pipeline will produce non-deterministic results due to race conditions.
Option B is correct because using a stateful lambda (one that mutates shared mutable state) inside a parallel stream's map operation introduces race conditions. The map operation is intended to be stateless and non-interfering; when multiple threads concurrently update a shared counter without proper synchronization, the result becomes non-deterministic and unpredictable.
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.
- ✗
The pipeline will produce correct results if the stateful lambda is synchronized.
Why it's wrong here
Synchronization can cause contention and degrade performance, but it may work; however, it is not a recommended approach and may still have ordering issues.
- ✓
The pipeline will produce non-deterministic results due to race conditions.
Why this is correct
Stateful lambdas in parallel streams are discouraged because they introduce shared mutable state that leads to race conditions and unpredictable results.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The pipeline will throw a ConcurrentModificationException.
Why it's wrong here
ConcurrentModificationException occurs when the stream source is modified during iteration, not due to stateful lambda.
- ✗
The pipeline will always produce the same result regardless of parallelism.
Why it's wrong here
Parallel stream processing with stateful lambda is inherently non-deterministic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume synchronization or thread-safety fixes the issue, but the Streams API's contract requires stateless lambdas for correctness in parallel pipelines, and synchronization does not restore deterministic behavior or guarantee correct results.
Detailed technical explanation
How to think about this question
Under the hood, parallel streams use the ForkJoinPool to split the source into substreams, process them concurrently, and then merge results. A stateful lambda in map() violates the stateless requirement of the Streams API; even with synchronization, the order of updates is not guaranteed, leading to incorrect counts. In real-world scenarios, this often manifests as intermittent bugs that are hard to reproduce, making it a common pitfall in high-throughput data processing.
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.
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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: The pipeline will produce non-deterministic results due to race conditions. — Option B is correct because using a stateful lambda (one that mutates shared mutable state) inside a parallel stream's map operation introduces race conditions. The map operation is intended to be stateless and non-interfering; when multiple threads concurrently update a shared counter without proper synchronization, the result becomes non-deterministic and unpredictable.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 →
Same concept, more angles
1 more ways this is tested on 1Z0-829
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer uses a stateful lambda in a parallel stream. Which of the following is a potential consequence?
medium- ✓ A.Non-deterministic results
- B.ConcurrentModificationException
- C.All of the above
- D.Improved performance
Why A: Stateful lambdas can lead to non-deterministic results in parallel streams because shared mutable state creates race conditions.
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Last reviewed: Jun 25, 2026
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