1Z0-829 Working with Arrays and Collections Practice Question
What does the following code print? List<Integer> list = new ArrayList<>(List.of(1,2,3)); list.replaceAll(x -> x * 2); System.out.println(list);
⚠ Common exam trap
Many candidates think `replaceAll` doesn't exist on `List` or that it requires a `Comparator`, or they may confuse it with `replaceAll` on `Map` or `String`, leading them to incorrectly choose compilation failure (Option C).
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
✓
[2,4,6]
The `replaceAll` method on a `List` applies the given `UnaryOperator` to each element, replacing it with the result. Here, `x -> x * 2` multiplies each integer by 2, so the list becomes `[2, 4, 6]`. Option B is correct because the code compiles and runs, producing that 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.
- ✗
[2,3,4]
Why it's wrong here
Incorrect: not the result of doubling.
- ✓
[2,4,6]
Why this is correct
Correct: each element is doubled.
- ✗
Compilation fails
Why it's wrong here
The code compiles and runs.
- ✗
[1,4,9]
Why it's wrong here
Incorrect: wrong operation.
- ✗
[1,2,3]
Why it's wrong here
Incorrect: replaceAll modifies the list.
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