Question 34 of 513
1Z0-829 Working with Streams and Lambda Expressions Practice Question
Which statement about the Stream API is true?
⚠ Common exam trap
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.
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
✓
A stream can be consumed only once.
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.
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.
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.
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Last reviewed: Jun 30, 2026
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