- A
The Stream API does not modify the original data source.
Streams operate on a view of the data; they do not modify the underlying collection or array.
- B
Lambda expressions can capture variables that are effectively final.
Lambda expressions can capture local variables that are effectively final, meaning they are not reassigned after initialization.
- C
A stream can be consumed by multiple terminal operations sequentially.
Why wrong: A stream can have at most one terminal operation; after that, the stream is consumed and cannot be used again.
- D
Intermediate operations on a stream are executed eagerly.
Why wrong: Intermediate operations are lazy; they are not executed until a terminal operation is invoked.
- E
Lambda expressions introduce a new level of scope, similar to an anonymous inner class.
Why wrong: Lambda expressions do not introduce a new scope; they share the scope with the enclosing method, so variables from the outer scope are accessible directly.
Quick Answer
The correct answer is that lambda expressions can capture variables that are effectively final, and the Stream API operates on a view of the data without modifying the source. This is because the Stream API’s non-interference guarantee ensures that operations like filter, map, and collect produce new streams or results while leaving the original collection, array, or I/O source untouched—a core principle for safe parallel execution and functional programming. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this concept tests your understanding of Stream API characteristics and operations, often appearing in questions that pair non-modification with lazy evaluation or variable capture. A common trap is assuming streams modify the source or that captured variables must be explicitly declared final; instead, remember that any variable used in a lambda must be effectively final—its value never changes after initialization. Memory tip: think “no mutation, no modification” for streams, and “final in spirit, not in syntax” for captured variables.
1Z0-829 Working with Streams and Lambda Expressions Practice Question
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 are true about the Stream API and lambda expressions in Java 17?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The Stream API does not modify the original data source.
Option A is correct because the Stream API is designed to work on a view of the data, not the data itself. Operations like filter, map, and collect produce new streams or results without altering the original collection, array, or I/O source. This non-interference guarantee is a core principle of the Stream API, ensuring safe parallel execution and functional programming style.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The Stream API does not modify the original data source.
Why this is correct
Streams operate on a view of the data; they do not modify the underlying collection or array.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Lambda expressions can capture variables that are effectively final.
Why this is correct
Lambda expressions can capture local variables that are effectively final, meaning they are not reassigned after initialization.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
A stream can be consumed by multiple terminal operations sequentially.
Why it's wrong here
A stream can have at most one terminal operation; after that, the stream is consumed and cannot be used again.
- ✗
Intermediate operations on a stream are executed eagerly.
Why it's wrong here
Intermediate operations are lazy; they are not executed until a terminal operation is invoked.
- ✗
Lambda expressions introduce a new level of scope, similar to an anonymous inner class.
Why it's wrong here
Lambda expressions do not introduce a new scope; they share the scope with the enclosing method, so variables from the outer scope are accessible directly.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the lazy evaluation of intermediate operations with eager execution, or mistakenly believe a stream can be reused after a terminal operation, leading them to select options C or D.
Detailed technical explanation
How to think about this question
Under the hood, the Stream API uses internal iteration and a pipeline architecture where intermediate operations are combined into a single pass during the terminal operation. The effectively final requirement for captured variables in lambdas is enforced by the compiler to prevent race conditions in parallel streams; a variable is effectively final if its value does not change after initialization, even if not declared with the final keyword. In real-world scenarios, this prevents subtle bugs when streams are parallelized, as mutable captured variables would cause data inconsistency.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 1Z0-829 question test?
Working with Streams and Lambda Expressions — This question tests Working with Streams and Lambda Expressions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Stream API does not modify the original data source. — Option A is correct because the Stream API is designed to work on a view of the data, not the data itself. Operations like filter, map, and collect produce new streams or results without altering the original collection, array, or I/O source. This non-interference guarantee is a core principle of the Stream API, ensuring safe parallel execution and functional programming style.
What should I do if I get this 1Z0-829 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
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 →
Same concept, more angles
3 more ways this is tested on 1Z0-829
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 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.
hard- ✓ A.The peek() method is an intermediate operation.
- B.The collect() method is an intermediate operation.
- ✓ C.The findFirst() method returns an Optional.
- D.A stream can be traversed multiple times.
- E.The map() method returns a stream of the same type.
Why A: 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.
Variation 2. Which two statements about the Stream API are true? (Choose two.)
easy- ✓ A.The 'reduce()' operation can produce a result of a different type than the stream elements.
- B.The 'flatMap()' operation is a terminal operation.
- ✓ C.The 'findFirst()' operation is a short-circuiting terminal operation.
- D.The 'collect()' operation is an intermediate operation.
- E.Streams can be reused after a terminal operation.
Why A: Options B and C are true. B: findFirst() is short-circuiting and terminal. C: reduce() with identity, accumulator, and combiner can produce a different type. A is false because streams cannot be reused after a terminal operation. D is false because collect() is terminal. E is false because flatMap() is intermediate.
Variation 3. Which statement about the Stream API is true?
easy- A.Parallel streams always improve performance.
- B.Streams are always finite.
- C.Intermediate operations are executed eagerly.
- ✓ D.A stream can be consumed only once.
Why D: 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.
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Last reviewed: Jun 11, 2026
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