This 1Z0-829 practice question tests your understanding of working with streams and lambda expressions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 statement about the Stream API is true?
Parallel streams always improve performance.
Why wrong: Not always; depends on context.
Streams are always finite.
Why wrong: Infinite streams exist.
Intermediate operations are executed eagerly.
Why wrong: They are lazy.
A stream can be consumed only once.
Correct.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
A stream can be consumed only once.
Option D is correct because a Stream in Java represents a sequence of elements that can be traversed only once. Once a terminal operation (like collect() or forEach()) is invoked on a stream, the stream is consumed and cannot be reused; attempting to do so throws an IllegalStateException. This one-time consumption is a fundamental design principle of the Stream API, ensuring that operations are applied to a single, immutable 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.
Parallel streams always improve performance.
Why it's wrong here
Not always; depends on context.
Streams are always finite.
Why it's wrong here
Infinite streams exist.
Intermediate operations are executed eagerly.
Why it's wrong here
They are lazy.
A stream can be consumed only once.
Why this is correct
Correct.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Oracle often tests the misconception that streams are reusable like collections, but the trap here is that candidates forget a stream is a one-shot object that cannot be traversed more than once, leading them to incorrectly assume they can call multiple terminal operations on the same stream.
Detailed technical explanation
Under the hood, a Stream is a wrapper around a data source (e.g., a collection, an I/O channel, or a generator function) that implements the BaseStream interface. The one-time consumption is enforced by the stream pipeline's internal state: once a terminal operation triggers the traversal, the stream's source is marked as consumed, and any subsequent attempt to call a terminal operation on the same stream reference results in an IllegalStateException. This design ensures that operations are deterministic and side-effect-free, which is critical for parallel processing where the stream may be split and processed by multiple threads.
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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Working with Streams and Lambda Expressions — study guide chapter
Learn the concepts, then practise the questions
Working with Streams and Lambda Expressions practice questions
Targeted practice on this topic area only
All 1Z0-829 questions
509 questions across all exam domains
Oracle Certified Professional Java SE 17 Developer 1Z0-829 study guide
Full concept coverage aligned to exam objectives
1Z0-829 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 1Z0-829 questions linked to Handling Date, Time, Text, Numeric and Boolean Values.
Practise 1Z0-829 questions linked to Controlling Program Flow.
Practise 1Z0-829 questions linked to Utilizing Java Object-Oriented Approach.
Practise 1Z0-829 questions linked to Handling Exceptions.
Practise 1Z0-829 questions linked to Working with Arrays and Collections.
Practise 1Z0-829 questions linked to Working with Streams and Lambda Expressions.
Practise 1Z0-829 questions linked to Java Platform Overview and Packaging.
Practise 1Z0-829 questions linked to Java I/O API and Securing Applications.
Practise 1Z0-829 questions linked to 1Z0-829 fundamentals.
Practise 1Z0-829 questions linked to 1Z0-829 scenario.
Practise 1Z0-829 questions linked to 1Z0-829 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: A stream can be consumed only once. — Option D is correct because a Stream in Java represents a sequence of elements that can be traversed only once. Once a terminal operation (like collect() or forEach()) is invoked on a stream, the stream is consumed and cannot be reused; attempting to do so throws an IllegalStateException. This one-time consumption is a fundamental design principle of the Stream API, ensuring that operations are applied to a single, immutable 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
Last reviewed: Jun 30, 2026
This 1Z0-829 practice question is part of Courseiva's free Oracle certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 1Z0-829 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.