- A
list.parallelStream().map(s -> s.toUpperCase()).forEach(System.out::print);
Why wrong: In a parallel stream, forEach does not guarantee encounter order; output order may be inconsistent.
- B
list.parallelStream().map(s -> s.toUpperCase()).forEachOrdered(System.out::print);
forEachOrdered ensures that processing respects the encounter order, even in a parallel stream.
- C
list.stream().parallel().map(s -> { synchronized(System.out) { return s.toUpperCase(); } }).forEach(System.out::print);
Why wrong: Synchronizing on System.out and applying inside map is unnecessary and will cause performance degradation.
- D
list.stream().parallel().map(s -> s.toUpperCase()).sequential().forEach(System.out::print);
Why wrong: Calling sequential() after parallel() reverts to sequential processing, losing parallelism.
Quick Answer
The correct and most appropriate change is to use `parallelStream()` with `forEachOrdered()`. This preserves the encounter order of the original list while still enabling parallel processing, because `forEachOrdered` guarantees that elements are processed in the order they appear in the stream, even across multiple threads. In contrast, `forEach` in a parallel stream does not respect order, and `sequential()` would defeat the purpose of parallelism. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of the trade-off between parallelism and ordering—a common trap is assuming `forEach` works in parallel, but only `forEachOrdered` maintains order. A useful memory tip: think of "Ordered" as the key that locks in sequence, even when threads are free.
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. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 writes the following code to print a list of strings in order: list.stream().map(s -> s.toUpperCase()).forEach(System.out::print). They want to parallelize the processing but must preserve the output order. Which change is correct and most appropriate?
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
list.parallelStream().map(s -> s.toUpperCase()).forEachOrdered(System.out::print);
Option C is correct because parallelStream() returns a parallel stream, and forEachOrdered guarantees encounter order while still allowing parallel processing (though ordering may reduce some parallelism). Option A is wrong because forEach does not preserve order in parallel streams. Option B is wrong because sequential() would lose parallelism. Option D is wrong because synchronized is unnecessary and reduces performance.
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.
- ✗
list.parallelStream().map(s -> s.toUpperCase()).forEach(System.out::print);
Why it's wrong here
In a parallel stream, forEach does not guarantee encounter order; output order may be inconsistent.
- ✓
list.parallelStream().map(s -> s.toUpperCase()).forEachOrdered(System.out::print);
Why this is correct
forEachOrdered ensures that processing respects the encounter order, even in a parallel stream.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
list.stream().parallel().map(s -> { synchronized(System.out) { return s.toUpperCase(); } }).forEach(System.out::print);
Why it's wrong here
Synchronizing on System.out and applying inside map is unnecessary and will cause performance degradation.
- ✗
list.stream().parallel().map(s -> s.toUpperCase()).sequential().forEach(System.out::print);
Why it's wrong here
Calling sequential() after parallel() reverts to sequential processing, losing parallelism.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
In a parallel stream, forEach does not guarantee encounter order; output order may be inconsistent.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 1Z0-829 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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: list.parallelStream().map(s -> s.toUpperCase()).forEachOrdered(System.out::print); — Option C is correct because parallelStream() returns a parallel stream, and forEachOrdered guarantees encounter order while still allowing parallel processing (though ordering may reduce some parallelism). Option A is wrong because forEach does not preserve order in parallel streams. Option B is wrong because sequential() would lose parallelism. Option D is wrong because synchronized is unnecessary and reduces performance.
What should I do if I get this 1Z0-829 question wrong?
Identify which 1Z0-829 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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