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 TWO statements about the Stream API are correct? (Choose two.) A. A stream can be traversed multiple times. B. The peek() method is an intermediate operation. C. The findFirst() method returns an Optional. D. The collect() method is an intermediate operation. E. The map() method returns a stream of the same type.
The peek() method is an intermediate operation.
Correct.
The collect() method is an intermediate operation.
Why wrong: It is a terminal operation.
The findFirst() method returns an Optional.
Correct.
A stream can be traversed multiple times.
Why wrong: Streams can only be consumed once.
The map() method returns a stream of the same type.
Why wrong: It can return a different type.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The peek() method is an intermediate operation.
Option A is correct because the `peek()` method is an intermediate operation in the Stream API. Intermediate operations return a new stream and are lazy; they are not executed until a terminal operation is invoked. `peek()` allows you to inspect elements as they flow through the pipeline without modifying them.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The peek() method is an intermediate operation.
Why this is correct
Correct.
Related concept
Read the scenario before looking for a memorised answer.
The collect() method is an intermediate operation.
Why it's wrong here
It is a terminal operation.
The findFirst() method returns an Optional.
Why this is correct
Correct.
Related concept
Read the scenario before looking for a memorised answer.
A stream can be traversed multiple times.
Why it's wrong here
Streams can only be consumed once.
The map() method returns a stream of the same type.
Why it's wrong here
It can return a different type.
Common exam traps
Oracle often tests the distinction between intermediate and terminal operations, and the trap here is that candidates confuse `collect()` (terminal) with an intermediate operation or assume `map()` always returns the same stream type, while in reality it can change the element type via the provided function.
Detailed technical explanation
Under the hood, intermediate operations like `peek()` and `map()` are added to a pipeline of operations that are evaluated lazily. The `peek()` method is primarily intended for debugging, as it allows you to observe elements as they pass through the pipeline, but it should not be used for side effects in production code because the Stream API does not guarantee that `peek()` will be invoked for every element in all scenarios (e.g., with short-circuiting operations). The `findFirst()` method returns an `Optional` to safely handle the case where the stream is empty, avoiding null pointer exceptions.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Working with Streams and Lambda Expressions — This question tests Working with Streams and Lambda Expressions — Read the scenario before looking for a memorised answer..
The correct answer is: The peek() method is an intermediate operation. — Option A is correct because the `peek()` method is an intermediate operation in the Stream API. Intermediate operations return a new stream and are lazy; they are not executed until a terminal operation is invoked. `peek()` allows you to inspect elements as they flow through the pipeline without modifying them.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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