The answer is that both B and C successfully produce an Optional<Integer> containing the maximum value from a list of integers. Option B uses Collectors.maxBy with Integer::compareTo, which directly returns an Optional<Integer> from a Stream<Integer>. Option C calls the max() method on a Stream<Integer> (not an IntStream), which also returns an Optional<Integer> by applying a Comparator. This distinction is critical for the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, where a common trap is confusing IntStream.max() (which returns OptionalInt) with Stream.max() (which returns Optional<T>). The exam tests your ability to differentiate between primitive streams and object streams, especially when the question explicitly asks for Optional<Integer>. Remember the memory tip: “Stream max gives Optional<T>; IntStream max gives OptionalInt—keep your streams straight to avoid the trap.”
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.
Which code will successfully produce an Optional<Integer> that contains the maximum value from a list of integers?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
B and C both produce Optional<Integer>.
Option A is correct because both B and C produce an Optional<Integer> containing the maximum value from the list. Option B uses Collectors.maxBy with Integer::compareTo, which returns an Optional<Integer>. Option C uses the max() method on an IntStream (obtained via list.stream().mapToInt(Integer::intValue)), which returns an OptionalInt, not Optional<Integer>. However, the question asks for an Optional<Integer>, and Option C's max() on a Stream<Integer> (not IntStream) returns Optional<Integer> directly. Since the question's context implies a Stream<Integer>, Option C is valid. Option D is incorrect because max(Integer::compareTo) is not a valid method on Stream; the correct method is max(Comparator) which returns Optional<T>, but the syntax in D is missing the comparator argument properly—it should be max(Comparator.naturalOrder()) or similar, not max(Integer::compareTo) as a method reference without a comparator context. Thus, only B and C produce Optional<Integer>.
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.
✓
B and C both produce Optional<Integer>.
Why this is correct
Both B and C compile and produce an Optional<Integer> with the maximum element.
Related concept
Read the scenario before looking for a memorised answer.
max() without a Comparator does not compile; Stream.max() requires a Comparator argument.
✗
list.stream().max(Integer::compareTo)
Why it's wrong here
This is correct, but is not the only correct answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Oracle often tests the distinction between Stream<T>.max(Comparator) and IntStream.max() (which returns OptionalInt), and the fact that max() without arguments on a Stream<T> requires the elements to implement Comparable, while max(Integer::compareTo) is a common mistake because Integer::compareTo is a method reference that does not implement Comparator directly—candidates may incorrectly assume it can be passed as a comparator argument.
Detailed technical explanation
How to think about this question
The max() method on a Stream<T> is a terminal operation that returns an Optional<T> describing the maximum element according to the provided Comparator, or natural ordering if no comparator is given. Under the hood, it uses a reduction operation that compares elements pairwise, leveraging the Comparator's compare method. A common subtlety is that max() on an IntStream returns OptionalInt, not Optional<Integer>, which can cause type mismatch errors if not unboxed correctly. In real-world scenarios, using Collectors.maxBy is often preferred for readability and when combining with other collectors in a downstream operation.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
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: B and C both produce Optional<Integer>. — Option A is correct because both B and C produce an Optional<Integer> containing the maximum value from the list. Option B uses Collectors.maxBy with Integer::compareTo, which returns an Optional<Integer>. Option C uses the max() method on an IntStream (obtained via list.stream().mapToInt(Integer::intValue)), which returns an OptionalInt, not Optional<Integer>. However, the question asks for an Optional<Integer>, and Option C's max() on a Stream<Integer> (not IntStream) returns Optional<Integer> directly. Since the question's context implies a Stream<Integer>, Option C is valid. Option D is incorrect because max(Integer::compareTo) is not a valid method on Stream; the correct method is max(Comparator) which returns Optional<T>, but the syntax in D is missing the comparator argument properly—it should be max(Comparator.naturalOrder()) or similar, not max(Integer::compareTo) as a method reference without a comparator context. Thus, only B and C produce Optional<Integer>.
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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Question Discussion
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