Working with Streams and Lambda Expressions →hardMultiple SelectObjective-mapped

1Z0-829 Working with Streams and Lambda Expressions Practice Question

Which TWO are correct about parallel streams in Java? (Choose TWO.)

⚠ Common exam trap

Watch out — candidates often assume parallel streams are always faster (Option A) or that any lambda is safe (Option B), overlooking the critical requirements of statelessness and non-interference for correctness in parallel execution.

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

✓

Parallel streams use the common ForkJoinPool by default.

Parallel streams in Java, by default, use the common ForkJoinPool (ForkJoinPool.commonPool()), which is a shared thread pool designed for parallel task execution. This pool is lazily initialized and has a default parallelism level equal to the number of available processors minus one, as per the ForkJoinPool implementation.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Parallel streams always improve performance over sequential streams.
Why it's wrong here
Performance depends on data size and operation complexity.
✗
Any lambda expression is safe to use in a parallel stream.
Why it's wrong here
Lambdas must be stateless and non-interfering.
✗
Using parallel streams guarantees the order of elements in the result.
Why it's wrong here
Order is not guaranteed unless using forEachOrdered.
✓
Parallel streams use the common ForkJoinPool by default.
Why this is correct
Default pool is ForkJoinPool.commonPool().
✓
To get correct results, operations should be stateless and non-interfering.
Why this is correct
Statelessness ensures correct parallel execution.

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1Z0-829 Working with Streams and Lambda Expressions Practice Question

Why each option matters

Option-by-option breakdown

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