Given the code fragment: List<String> gwords = Arrays.asList("why ", "what ", "when "); BinaryOperator<String> operator = (s1, s2) -> s1.concat(s2); // line n1 String sen = gwords.stream()…

Question

Options

• AWord: why what when
• BWord: whyWord: why what Word: why what when
• CWord:why Word:what Word:when
• DCompilation fails at line n1.

• A
  79% (30)
• B
  8% (3)
• C
  11% (4)
• D
  3% (1)

Explanation

reduce(identity, accumulator) folds the stream left, starting with the identity and applying the accumulator once per element in sequence: "Word: " → concat("why ") → "Word: why " → concat("what ") → "Word: why what " → concat("when ") → "Word: why what when ". That single accumulated string is what gets printed, making A correct.

B is wrong because it shows three progressive sub-results concatenated together ("Word: why", "Word: why what", "Word: why what when"), as if each intermediate accumulation was appended to the output - reduce doesn't expose or accumulate intermediate results that way.

C is wrong because it implies the identity "Word: " was prefixed to each element individually, which would be a map operation, not a reduce.

D is wrong because line n1 compiles perfectly: a lambda (s1, s2) -> s1.concat(s2) matches BinaryOperator<String> exactly - two String parameters, one String return.

Memory tip: Think of reduce(identity, op) as a running total - the identity is your starting value and each stream element updates it exactly once, left to right. The final value, not any intermediate step, is what you get back.

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