Working with Streams and Lambda Expressions →mediumMultiple ChoiceObjective-mapped

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

A developer adds .peek(System.out::println) to a stream pipeline to debug, but no output is printed. What is the most likely reason?

⚠ Common exam trap

Test-takers frequently assume intermediate operations execute eagerly or that peek() works like a standalone print statement, overlooking the fundamental lazy-evaluation contract of streams.

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 pipeline lacks a terminal operation

Stream pipelines are lazy; intermediate operations like peek() are only executed when a terminal operation (e.g., forEach, collect, reduce) is invoked. Without a terminal operation, the pipeline never starts processing data, so peek() produces no output.

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 is parallel
Why it's wrong here
Parallel streams still execute; the issue is not parallelism.
✓
The pipeline lacks a terminal operation
Why this is correct
Correct. Without a terminal operation, the pipeline never executes, so peek never runs.
✗
The peek operation is placed after the terminal operation
Why it's wrong here
Terminal operations end the pipeline; peek must be placed before the terminal operation.
✗
The stream is empty
Why it's wrong here
Even if empty, peek would not execute, but the presence of a terminal operation would show that no elements are processed; however, the question states no output, so the pipeline is not executed at all.

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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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