The correct approach is to first count the positive numbers, then create an array of that exact size and fill it. This method is optimal because it avoids the memory waste of a fixed-size array with trailing zeros and eliminates the overhead of dynamic resizing or boxing. By performing a single pass to count positives and a second pass to populate the result, you achieve O(n) time complexity with minimal memory overhead—exactly what the legacy code needs for large arrays up to one million elements. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of primitive array efficiency versus collection-based or stream-based solutions; a common trap is assuming ArrayList or streams are always simpler, but they introduce boxing overhead or resizing costs. Remember the memory tip: "Count first, then fill—no zeros, no thrills."
1Z0-811 Arrays and Methods Practice Question
This 1Z0-811 practice question tests your understanding of arrays and methods. 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.
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?
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.
Option C is correct because 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.
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.
✗
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a linked list and then convert.
Why it's wrong here
LinkedList is memory-inefficient and conversion requires iteration.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
Under the hood, the two-pass counting approach uses primitive int arrays directly, avoiding object overhead and garbage collection pressure. For arrays up to 1 million elements, the difference in memory between int[] (4 bytes per element) and Integer[] (16–24 bytes per element due to object headers) is substantial. Real-world scenarios like processing sensor data or log files often require this pattern to stay within heap limits.
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 1Z0-811 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Arrays and Methods — This question tests Arrays and Methods — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: First count positives, then create an array of that exact size, fill it. — Option C is correct because 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.
What should I do if I get this 1Z0-811 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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Question Discussion
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