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.
List<Integer> numbers = List.of(1, 2, 3, 4, 5);
int sum = numbers.stream()
.reduce(0, (a, b) -> a + b);
System.out.println(sum);Refer to the exhibit. What is the output?
List<Integer> numbers = List.of(1, 2, 3, 4, 5);
int sum = numbers.stream()
.reduce(0, (a, b) -> a + b);
System.out.println(sum);0
Why wrong: Incorrect; identity is used as starting value but final sum is 15.
15
Correct.
10
Why wrong: Incorrect; sum of 1 to 5 is 15.
5
Why wrong: Incorrect.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
15
The stream pipeline starts with `IntStream.rangeClosed(0, 5)` producing the integers 0, 1, 2, 3, 4, 5. The filter passes all these values, and the map is an identity function (or absent). The reduction sums them: 0+1+2+3+4+5 = 15. Therefore, the output is 15.
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.
0
Why it's wrong here
Incorrect; identity is used as starting value but final sum is 15.
15
Why this is correct
Correct.
Related concept
Read the scenario before looking for a memorised answer.
10
Why it's wrong here
Incorrect; sum of 1 to 5 is 15.
5
Why it's wrong here
Incorrect.
Common exam traps
The trap here is that candidates often miscount the number of elements produced by `rangeClosed` versus `range`, leading to off-by-one errors in the sum.
Detailed technical explanation
The `IntStream.rangeClosed(0, 5)` method generates a sequential ordered stream of ints from 0 inclusive to 5 inclusive, producing 6 elements. The `reduce(0, Integer::sum)` operation is a terminal reduction that starts with an identity value (0) and applies the accumulator function (sum) to each element, effectively computing the sum of all elements. This is equivalent to `IntStream.rangeClosed(0, 5).sum()`. Understanding the difference between `range` (exclusive end) and `rangeClosed` (inclusive end) is critical for accurate stream size calculations.
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: 15 — The stream pipeline starts with `IntStream.rangeClosed(0, 5)` producing the integers 0, 1, 2, 3, 4, 5. The filter passes all these values, and the map is an identity function (or absent). The reduction sums them: 0+1+2+3+4+5 = 15. Therefore, the output is 15.
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: Jul 4, 2026
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