Quick Answer
The correct answer is reduce, along with forEach, as both are terminal operations on a stream. In the Java Stream API, terminal operations produce a non-stream result or a side effect, ending the pipeline; intermediate operations, by contrast, return a new stream and are lazy, meaning they only execute when 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 that methods like filter, map, and sorted are intermediate, while forEach, reduce, collect, and count are terminal. A common trap is confusing forEach with peek—peek is intermediate and used for debugging, whereas forEach terminates the stream. To remember, think of the pipeline as a factory line: intermediate operations are the workers that modify the product, but nothing ships until a terminal operation like reduce or forEach hits the “stop” button.
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 of the following are terminal operations on a stream? (Choose two.)
forEach
forEach is a terminal operation that performs an action on each element.
distinct
Why wrong: distinct is an intermediate operation that removes duplicates.
reduce
reduce is a terminal operation that performs a reduction on elements.
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.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
forEach
Option A is correct because `forEach` is a terminal operation that consumes the stream, applying the provided action to each element and producing a side effect without returning a new stream. Option C is correct because `reduce` is a terminal operation that combines stream elements into a single result using an associative accumulation function, terminating the stream pipeline.
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.
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.
distinct
Why it's wrong here
distinct is an intermediate operation that removes duplicates.
reduce
Why this is correct
reduce is a terminal operation that performs a reduction on elements.
Related concept
Read the scenario before looking for a memorised answer.
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.
Common exam traps
The trap here is that candidates often confuse intermediate operations like `distinct`, `filter`, and `map` with terminal operations because they also process elements, but they do not produce a final result or side effect that terminates the stream.
Detailed technical explanation
Terminal operations trigger the processing of the stream pipeline and close the stream; they are evaluated eagerly, while intermediate operations are lazy. `reduce` uses a `BinaryOperator` to perform reduction, and its identity and combiner must be associative to ensure correct parallel execution. `forEach` is a terminal operation that does not guarantee encounter order for parallel streams unless `forEachOrdered` is used.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
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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: forEach — Option A is correct because `forEach` is a terminal operation that consumes the stream, applying the provided action to each element and producing a side effect without returning a new stream. Option C is correct because `reduce` is a terminal operation that combines stream elements into a single result using an associative accumulation function, terminating the stream pipeline.
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 25, 2026
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