- A
Use Files.readAllLines() to read the entire file into memory, then process in parallel using streams.
Why wrong: readAllLines() loads the entire file into memory, causing OOM with large files and limited heap.
- B
Use a BufferedReader on a separate thread, reading lines into a bounded queue, and a thread pool to process rows from the queue.
This approach reads line by line, using a bounded queue to decouple reading and processing.
- C
Use a FileChannel with a memory-mapped byte buffer of the entire file.
Why wrong: Memory-mapping the entire file would also exceed the heap (maps are off-heap but still consume address space; could cause issues).
- D
Use a java.nio.file.FileSystem with a WatchService to detect changes to the file.
Why wrong: WatchService is for monitoring directory changes, not for reading file contents.
Quick Answer
The answer is a bounded blocking queue paired with a thread pool, because this design directly addresses the core challenge of processing a large file under severe memory constraints. The bounded queue acts as a back-pressure mechanism, preventing the I/O thread from flooding memory with rows from the 500 MB CSV file when the CPU-bound processing cannot keep up, thus protecting the 512 MB heap from exhaustion. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this scenario tests your understanding of concurrency patterns for resource-limited environments, often appearing as a trap where candidates choose an unbounded queue or a single-threaded approach. The key insight is that a bounded queue decouples I/O latency from CPU work while enforcing a memory cap. Remember the mnemonic: **Bounded Back-pressure Blocks Bloat** — always choose a bounded queue when heap is smaller than the file.
1Z0-829 Java I/O API and Securing Applications Practice Question
This 1Z0-829 practice question tests your understanding of java i/o api and securing applications. 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.
An architect is designing a microservice that reads large CSV files (up to 500 MB) from a shared filesystem and processes each row. The processing is CPU-bound and must not block the main thread. The service is deployed in a container with limited memory (512 MB heap). Which approach is most suitable?
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
Use a BufferedReader on a separate thread, reading lines into a bounded queue, and a thread pool to process rows from the queue.
Option B is correct because it uses a bounded blocking queue to decouple I/O (reading lines from the CSV) from CPU-bound processing, preventing the main thread from being blocked while also avoiding memory exhaustion. The bounded queue acts as a back-pressure mechanism, ensuring that the limited 512 MB heap is not overwhelmed by the 500 MB file. Processing rows via a thread pool allows parallel CPU-bound work without blocking the reading thread.
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 Files.readAllLines() to read the entire file into memory, then process in parallel using streams.
Why it's wrong here
readAllLines() loads the entire file into memory, causing OOM with large files and limited heap.
- ✓
Use a BufferedReader on a separate thread, reading lines into a bounded queue, and a thread pool to process rows from the queue.
Why this is correct
This approach reads line by line, using a bounded queue to decouple reading and processing.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a FileChannel with a memory-mapped byte buffer of the entire file.
Why it's wrong here
Memory-mapping the entire file would also exceed the heap (maps are off-heap but still consume address space; could cause issues).
- ✗
Use a java.nio.file.FileSystem with a WatchService to detect changes to the file.
Why it's wrong here
WatchService is for monitoring directory changes, not for reading file contents.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume memory-mapped files (FileChannel) are always efficient for large files, but they ignore the memory constraint and the need to keep the main thread responsive; Cisco tests whether you understand that bounded queues and separate threads are required for back-pressure and non-blocking processing in constrained environments.
Detailed technical explanation
How to think about this question
Under the hood, a BufferedReader wrapped around a FileReader reads the file in chunks (default buffer size 8192 bytes), so only a small portion of the file is in memory at any time. The bounded queue (e.g., ArrayBlockingQueue) uses internal locks and conditions to block the producer (reader thread) when the queue is full, providing natural flow control. This pattern is a classic producer-consumer design, which is ideal for scenarios where I/O latency varies and CPU work is expensive, as it prevents the reader from outpacing the processors and causing heap exhaustion.
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
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FAQ
Questions learners often ask
What does this 1Z0-829 question test?
Java I/O API and Securing Applications — This question tests Java I/O API and Securing Applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a BufferedReader on a separate thread, reading lines into a bounded queue, and a thread pool to process rows from the queue. — Option B is correct because it uses a bounded blocking queue to decouple I/O (reading lines from the CSV) from CPU-bound processing, preventing the main thread from being blocked while also avoiding memory exhaustion. The bounded queue acts as a back-pressure mechanism, ensuring that the limited 512 MB heap is not overwhelmed by the 500 MB file. Processing rows via a thread pool allows parallel CPU-bound work without blocking the reading thread.
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
This 1Z0-829 practice question is part of Courseiva's free Oracle certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 1Z0-829 exam.
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