Quick Answer
The correct answer is `FileChannel.transferTo(long, long, WritableByteChannel)` because it leverages the operating system’s zero-copy data transfer mechanism, such as `sendfile()` on Linux or `TransmitFile()` on Windows, to move data directly from the file system cache to the target channel without any intermediate buffers or user-space copies. This eliminates unnecessary CPU overhead and memory bandwidth usage, making it the most efficient approach for transferring data between two channels on the same machine. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of NIO performance optimizations and often appears as a trap where less efficient alternatives like `ByteBuffer` loops or `FileInputStream.read()` are presented. A common memory tip: think “transferTo = zero copy, no middleman” — if you see any option involving a byte array or direct buffer allocation, it’s likely wrong.
This 1Z0-829 practice question tests your understanding of java i/o api and securing applications. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 class from the java.nio.file package is most appropriate for efficiently transferring data between two channels on the same machine?
Files.copy(Path, Path)
Why wrong: Uses streams; not zero-copy.
RandomAccessFile.getChannel().write(ByteBuffer)
Why wrong: Manual buffer copy; less efficient.
InputStream.transferTo(OutputStream)
Why wrong: Stream-based copy; not optimal for channels.
FileChannel.transferTo(long, long, WritableByteChannel)
Zero-copy transfer between channels.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
FileChannel.transferTo(long, long, WritableByteChannel)
Option D is correct because `FileChannel.transferTo()` (and its counterpart `transferFrom()`) uses the operating system's zero-copy mechanism (e.g., `sendfile()` on Linux or `TransmitFile()` on Windows) to move data directly between file system caches and the target channel without intermediate buffers or user-space copies. This makes it the most efficient approach for transferring data between two channels on the same machine, as it minimizes CPU overhead and memory bandwidth usage.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Files.copy(Path, Path)
Why it's wrong here
Uses streams; not zero-copy.
RandomAccessFile.getChannel().write(ByteBuffer)
Why it's wrong here
Manual buffer copy; less efficient.
InputStream.transferTo(OutputStream)
Why it's wrong here
Stream-based copy; not optimal for channels.
FileChannel.transferTo(long, long, WritableByteChannel)
Why this is correct
Zero-copy transfer between channels.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse high-level convenience methods like `Files.copy()` or `InputStream.transferTo()` with low-level channel operations, failing to recognize that the question specifically asks for 'most efficient' transfer between channels, which requires zero-copy via `FileChannel.transferTo()`.
Detailed technical explanation
Under the hood, `FileChannel.transferTo()` delegates to the OS's `sendfile()` system call (on Linux/Unix) or `TransmitFile()` (on Windows), which transfers data directly from the file cache to the target channel's socket or file descriptor without copying data through user space. A subtle behavior is that `transferTo()` may not transfer all requested bytes in a single call (e.g., due to platform limits like 2GB on some systems), so it must be called in a loop to ensure complete transfer. In real-world scenarios, this is critical for high-performance file servers or log aggregation tools where minimizing CPU usage during large file transfers is essential.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
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..
The correct answer is: FileChannel.transferTo(long, long, WritableByteChannel) — Option D is correct because `FileChannel.transferTo()` (and its counterpart `transferFrom()`) uses the operating system's zero-copy mechanism (e.g., `sendfile()` on Linux or `TransmitFile()` on Windows) to move data directly between file system caches and the target channel without intermediate buffers or user-space copies. This makes it the most efficient approach for transferring data between two channels on the same machine, as it minimizes CPU overhead and memory bandwidth usage.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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