The answer is to use a single temporary array and reuse it by copying data into it for each window. This optimization directly reduces GC overhead by eliminating the repeated allocation of short-lived arrays that occurs with the current System.arraycopy approach. When a method is called millions of times per minute on large arrays with small windows, each new array becomes garbage almost immediately, flooding the young generation and triggering frequent minor collections. On the Oracle Java Foundations 1Z0-811 exam, this scenario tests your understanding of object churn and how reusing mutable structures can dramatically improve performance in high-frequency loops. A common trap is assuming that array copy itself is the bottleneck, when in fact the allocation of many temporary objects is what drives GC overhead. Remember the memory tip: reuse to reduce refuse—one temporary array avoids a thousand short-lived allocations.
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 team is developing a financial application that processes large arrays of market data. They have a method that calculates moving averages by copying a subarray for each window. The current implementation creates a new array for each window using System.arraycopy. The application is running slowly in production. The team identifies that the method is called millions of times per minute. The array is large and the window size is small. The garbage collector overhead is high due to many short-lived arrays. Which optimization should they apply to reduce object creation and improve performance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a single temporary array and reuse it by copying data into it for each window.
Option B is correct because reusing a single temporary array eliminates the repeated allocation of short-lived arrays for each window, directly reducing garbage collector overhead. The current implementation uses System.arraycopy to create a new array per window, which is the primary source of object churn. By allocating one array once and copying data into it for each window, the team minimizes object creation while still performing the necessary copy operation.
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 a Stream to process the array without creating intermediate arrays.
Why it's wrong here
Streams may create objects and are not necessarily zero-copy.
✓
Use a single temporary array and reuse it by copying data into it for each window.
Why this is correct
Reuses one array, eliminating repeated allocations and reducing GC pressure.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use Arrays.copyOfRange() which is faster than System.arraycopy.
Why it's wrong here
Still creates a new array each time.
✗
Use ArrayList instead of array to avoid copy.
Why it's wrong here
ArrayList internally uses array, still requires copying and creates objects.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that using a more modern API (like Streams or copyOfRange) automatically improves performance, when in fact the key optimization is reducing object allocation frequency.
Detailed technical explanation
How to think about this question
Under the hood, System.arraycopy is a native method that performs a fast memory copy, but each call to it with a new destination array triggers allocation on the heap. Reusing a pre-allocated array avoids this allocation, but care must be taken to ensure the array is large enough for the window size and that data from previous windows does not leak. In real-world high-frequency trading systems, such micro-optimizations are critical because garbage collection pauses can cause missed market events.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: Use a single temporary array and reuse it by copying data into it for each window. — Option B is correct because reusing a single temporary array eliminates the repeated allocation of short-lived arrays for each window, directly reducing garbage collector overhead. The current implementation uses System.arraycopy to create a new array per window, which is the primary source of object churn. By allocating one array once and copying data into it for each window, the team minimizes object creation while still performing the necessary copy operation.
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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