Question 491 of 481
1Z0-811 Arrays and Methods Practice Question
A company's legacy code has a method that takes an array of integers and returns a new array containing only the positive numbers. The current implementation uses a fixed-size array equal to the input size and counts positive numbers, then copies them, but if many negatives exist, the result array has trailing zeros (which are removed by copying again). This wastes memory and time. The array can be large (up to 1 million elements). The developer wants to improve memory efficiency and runtime without using external libraries. Which approach should they implement?
⚠ Common exam trap
Oracle often tests the misconception that ArrayList or streams are always more efficient, but here the constraint 'without using external libraries' and the need for primitive efficiency make the two-pass counting approach the correct choice.
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
✓
First count positives, then create an array of that exact size, fill it.
It avoids the overhead of dynamic resizing (as in ArrayList) or boxing (as in streams) by first counting the positives in a single pass, then creating an exact-sized int[] array, and filling it in a second pass. This yields O(n) time complexity and minimal memory overhead, directly addressing the legacy code's inefficiency without external libraries.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use an ArrayList to collect positive numbers, then convert to int[].
Why it's wrong here
ArrayList resizes, leading to potential memory waste and multiple copies.
- ✗
Use a stream to filter and collect to array.
Why it's wrong here
Streams may have overhead and create intermediate objects.
- ✓
First count positives, then create an array of that exact size, fill it.
Why this is correct
Efficient: exactly allocated array, O(n) time.
- ✗
Use a linked list and then convert.
Why it's wrong here
LinkedList is memory-inefficient and conversion requires iteration.
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Last reviewed: Jun 30, 2026
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