Working with Arrays and Collections →mediumMultiple ChoiceObjective-mapped

1Z0-829 Working with Arrays and Collections Practice Question

A developer needs to sort a List of Employee objects by salary (double) in descending order. Which approach is correct and efficient?

⚠ Common exam trap

Watch out — candidates often choose the stream-based approach (Option B) thinking it is more modern or functional, but the exam tests understanding that `Collections.sort()` with a custom comparator is the correct and efficient way to sort a mutable list in-place, while streams create a new collection and are less efficient for this specific requirement.

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

✓

Collections.sort(list, (e1, e2) -> Double.compare(e2.getSalary(), e1.getSalary()));

It uses `Collections.sort()` with a custom `Comparator` that performs an in-place sort of the original list, which is both efficient (no new list created) and correctly orders by salary descending via `Double.compare(e2.getSalary(), e1.getSalary())`. This avoids the overhead of stream pipeline creation and collection, and directly mutates the list as required.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Collections.sort(list, Collections.reverseOrder());
Why it's wrong here
reverseOrder requires Comparable, not custom comparator.
✗
list.stream().sorted((e1, e2) -> Double.compare(e2.getSalary(), e1.getSalary())).collect(Collectors.toList());
Why it's wrong here
Creates new list, does not modify original.
✓
Collections.sort(list, (e1, e2) -> Double.compare(e2.getSalary(), e1.getSalary()));
Why this is correct
Uses Comparator with descending order via Double.compare.
✗
Collections.sort(list);
Why it's wrong here
Requires Employee to implement Comparable, not specified.

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1Z0-829 Working with Arrays and Collections Practice Question

Why each option matters

Option-by-option breakdown

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