Working with Arrays and Collections →mediumMultiple ChoiceObjective-mapped

1Z0-829 Working with Arrays and Collections Practice Question

Which of the following correctly sorts an array of integers (int[] arr) in descending order?

⚠ Common exam trap

Many exam-takers assume `Arrays.sort()` with a `Comparator` works on primitive arrays, but the Java API explicitly separates primitive and object array sorting, and the `Comparator` overload is only available for object arrays.

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

✓

Integer[] boxed = Arrays.stream(arr).boxed().toArray(Integer[]::new); Arrays.sort(boxed, Collections.reverseOrder()); arr = Arrays.stream(boxed).mapToInt(i->i).toArray();

It demonstrates the proper technique for sorting a primitive int array in descending order. The `Arrays.sort()` method does not accept a `Comparator` for primitive arrays, so the array must first be boxed into an `Integer[]` using `Arrays.stream(arr).boxed().toArray(Integer[]::new)`. After sorting with `Collections.reverseOrder()`, the result is unboxed back to `int[]` via `mapToInt(i->i).toArray()`. This approach correctly leverages the `Comparator` interface, which only works with object types.

Answer analysis

Option-by-option breakdown

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

✓
Integer[] boxed = Arrays.stream(arr).boxed().toArray(Integer[]::new); Arrays.sort(boxed, Collections.reverseOrder()); arr = Arrays.stream(boxed).mapToInt(i->i).toArray();
Why this is correct
Correct: this boxes the array, sorts descending, and unboxes back to int[].
✗
Arrays.sort(arr, Collections.reverseOrder());
Why it's wrong here
Incorrect: Arrays.sort with Comparator only works for object arrays, not primitive int[].
✗
None of the above, because primitive arrays cannot be sorted in descending order.
Why it's wrong here
Incorrect: descending sort is possible by using boxed arrays.
✗
Arrays.sort(arr, (a,b) -> b - a);
Why it's wrong here
Incorrect: the lambda cannot be applied to int[] directly; requires Integer[].
✗
Arrays.parallelSort(arr, (a,b) -> b - a);
Why it's wrong here
Incorrect: parallelSort also requires object array for Comparator.

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1Z0-829 Working with Arrays and Collections Practice Question

Why each option matters

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