- A
Integer[] boxed = Arrays.stream(arr).boxed().toArray(Integer[]::new); Arrays.sort(boxed, Collections.reverseOrder()); arr = Arrays.stream(boxed).mapToInt(i->i).toArray();
Correct: this boxes the array, sorts descending, and unboxes back to int[].
- B
Arrays.sort(arr, Collections.reverseOrder());
Why wrong: Incorrect: Arrays.sort with Comparator only works for object arrays, not primitive int[].
- C
None of the above, because primitive arrays cannot be sorted in descending order.
Why wrong: Incorrect: descending sort is possible by using boxed arrays.
- D
Arrays.sort(arr, (a,b) -> b - a);
Why wrong: Incorrect: the lambda cannot be applied to int[] directly; requires Integer[].
- E
Arrays.parallelSort(arr, (a,b) -> b - a);
Why wrong: Incorrect: parallelSort also requires object array for Comparator.
Quick Answer
The correct approach to sort a primitive int array in descending order in Java is to box the array into an Integer[], sort it with Collections.reverseOrder(), then unbox it back to int[]. This is necessary because the Arrays.sort() method for primitive types only supports ascending order and cannot accept a Comparator, which requires object types. By streaming the int[] with Arrays.stream(arr).boxed(), you convert each primitive to an Integer object, allowing you to sort using the reverse-order comparator. After sorting, you map back to int via mapToInt(i->i).toArray(). On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of the limitations of primitive arrays versus object arrays and the use of the Comparator interface. A common trap is attempting to use Arrays.sort(arr, Collections.reverseOrder()) directly on a primitive int[], which will not compile. Memory tip: think "box, sort reverse, unbox" — or simply "BSR-U" for the three-step pipeline.
1Z0-829 Working with Arrays and Collections Practice Question
This 1Z0-829 practice question tests your understanding of working with arrays and collections. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which of the following correctly sorts an array of integers (int[] arr) in descending order?
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();
Option A is correct because 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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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[].
Related concept
Read the scenario before looking for a memorised answer.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often 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.
Detailed technical explanation
How to think about this question
Under the hood, `Arrays.sort()` for primitives uses a dual-pivot quicksort algorithm, while the object overload uses TimSort with a `Comparator`. The boxing step creates `Integer` objects, which incurs memory overhead but is necessary to use `Collections.reverseOrder()`. In performance-critical code, you might manually reverse the array after an ascending sort to avoid boxing, but the exam expects knowledge of the correct API usage. The `Comparator.reverseOrder()` method returns a `Comparator<Integer>` that imposes the reverse of the natural ordering.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 1Z0-829 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 1Z0-829 question test?
Working with Arrays and Collections — This question tests Working with Arrays and Collections — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Integer[] boxed = Arrays.stream(arr).boxed().toArray(Integer[]::new); Arrays.sort(boxed, Collections.reverseOrder()); arr = Arrays.stream(boxed).mapToInt(i->i).toArray(); — Option A is correct because 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.
What should I do if I get this 1Z0-829 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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