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. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 converting legacy for loops to streams. The legacy code: List<Integer> list = new ArrayList<>(); for (String s : strings) { if (s.length() > 5) { list.add(s.length()); } } They write: List<Integer> list = strings.stream() .filter(s -> s.length() > 5) .map(s -> s.length()) .collect(Collectors.toList()); But it doesn't compile. The error is: 'cannot find symbol: method collect(Collector<Object,?,List<Object>>)'. What is the likely issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The map operation returns an IntStream, which does not have a collect method. Use map(s -> s.length()).boxed().collect(...) or mapToInt(...).boxed().
Option B is correct because the stream's type is String, but the pipeline returns an int (or Integer) after map; however, the error suggests the compiler cannot infer the collector type. The problem is that filter returns a Stream<String>, then map returns IntStream because s.length() returns int, and collect is not available on IntStream; they need to box it or use mapToInt then boxed. Option A is false because the lambda is valid. Option C is false because unordered would not affect compilation. Option D is false because the issue is not parallel.
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 lambda in filter is incorrectly written; it should be s.length > 5.
Why it's wrong here
The lambda syntax is correct; the error is not about the filter.
✓
The map operation returns an IntStream, which does not have a collect method. Use map(s -> s.length()).boxed().collect(...) or mapToInt(...).boxed().
Why this is correct
s.length() returns int, so map produces an IntStream. To collect to List<Integer>, you need to box to Stream<Integer>.
Related concept
Read the scenario before looking for a memorised answer.
✗
The stream should be made unordered to allow the collector to function.
Why it's wrong here
Unordered does not affect collect availability.
✗
Use parallelStream() to enable the collect method.
Why it's wrong here
Parallelism does not affect the availability of collect.
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.
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.
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 map operation returns an IntStream, which does not have a collect method. Use map(s -> s.length()).boxed().collect(...) or mapToInt(...).boxed(). — Option B is correct because the stream's type is String, but the pipeline returns an int (or Integer) after map; however, the error suggests the compiler cannot infer the collector type. The problem is that filter returns a Stream<String>, then map returns IntStream because s.length() returns int, and collect is not available on IntStream; they need to box it or use mapToInt then boxed. Option A is false because the lambda is valid. Option C is false because unordered would not affect compilation. Option D is false because the issue is not parallel.
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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Question Discussion
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