Given the code fragment: Stream<String> s1 = Stream.of("A", "B", "C", "B"); Stream<String> s2 = Stream.of("A", "D", "E", "B"); Stream.concat(s1, s2).parallel().distinct().forEach(element ->…

Question

Options

• AADEABCB // the order of element is unpredictable
• BABCE
• CABCDE // the order of elements is unpredictable
• DABBDE // the order of elements is unpredictable

• A
  17% (6)
• B
  9% (3)
• C
  6% (2)
• D
  69% (24)

Explanation

Option D as stated appears to be an error in the answer key - the actual correct answer should be C.

Here's why: Stream.concat(s1, s2) produces ["A","B","C","B","A","D","E","B"]. After .distinct(), duplicates are removed, leaving exactly five unique elements: A, B, C, D, E. Because .parallel() is applied before .forEach(), the terminal operation runs across threads with no guaranteed encounter order, so the print sequence is unpredictable - matching option C exactly.

Why the other choices fail:

• A (ADEABCB) contains 7 elements and preserves duplicates, ignoring that distinct() eliminates them.
• B (ABCE) is missing D, which is a distinct element present in s2.
• D (ABBDE) contains a duplicate B and omits C entirely - impossible after distinct(), which guarantees each element appears at most once regardless of parallelism.

Memory tip: Think of distinct() as a guarantee, not a hint - it always produces unique elements even in parallel pipelines (it uses a thread-safe ConcurrentHashMap internally). The only thing parallelism affects here is the print order via forEach, never the correctness of distinct(). If your answer has duplicates after distinct(), eliminate it immediately.

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