Quick Answer
The correct answer is collect, along with forEach and reduce, as these are the three terminal operations of the Stream interface. Terminal operations are distinct from intermediate operations because they produce a non-stream result or a side effect, and they trigger the processing of the pipeline, after which the stream is considered consumed and cannot be reused. In contrast, map and filter are intermediate operations that return a new stream and are lazily evaluated, meaning they do nothing until a terminal operation is invoked. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this distinction is frequently tested to ensure you understand the difference between operations that close the stream and those that merely transform it. A common trap is confusing reduce with an intermediate operation, but remember that reduce produces an Optional or a single value, not a stream. For a quick memory tip: think of terminal operations as the "finish line" — forEach, reduce, and collect all end the race, while map and filter keep the stream running.
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 three are terminal operations of the Stream interface? (Choose three.)
filter
Why wrong: filter is an intermediate operation that selects elements based on a predicate.
map
Why wrong: map is an intermediate operation that transforms elements.
reduce
reduce is a terminal operation that performs a reduction on the elements.
forEach
forEach is a terminal operation that performs an action on each element.
collect
collect is a terminal operation that accumulates elements into a collection or other result container.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
reduce
Option A (forEach), Option C (reduce), and Option E (collect) are terminal operations because they produce a result or side effect and close the stream. Option B (map) and Option D (filter) are intermediate operations; they return a stream and are lazy.
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.
filter
Why it's wrong here
filter is an intermediate operation that selects elements based on a predicate.
map
Why it's wrong here
map is an intermediate operation that transforms elements.
reduce
Why this is correct
reduce is a terminal operation that performs a reduction on the elements.
Related concept
Read the scenario before looking for a memorised answer.
forEach
Why this is correct
forEach is a terminal operation that performs an action on each element.
Related concept
Read the scenario before looking for a memorised answer.
collect
Why this is correct
collect is a terminal operation that accumulates elements into a collection or other result container.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
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
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.
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
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
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: reduce — Option A (forEach), Option C (reduce), and Option E (collect) are terminal operations because they produce a result or side effect and close the stream. Option B (map) and Option D (filter) are intermediate operations; they return a stream and are lazy.
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.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
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. Which TWO are terminal operations on the Stream interface? (Choose two.)
easyWhy A: A is correct because `count()` is a terminal operation that reduces the stream to a single `long` value by counting the number of elements after processing the pipeline. It triggers the stream pipeline execution and consumes the stream, making it a terminal operation per the `Stream` interface specification.
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Last reviewed: Jun 24, 2026
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