The answer is to use `DigestInputStream` wrapping the original stream, then read the stream. This is the most efficient approach because `DigestInputStream` is a built-in Java class that computes a message digest, such as an MD5 hash, on the fly as data is read from the underlying `InputStream`, eliminating the need to buffer the entire stream into memory. For the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of the `java.security` package and stream decorators, often appearing in scenarios involving large or streaming data sources where memory efficiency is critical. A common trap is attempting to read the entire stream into a byte array first and then compute the hash, which wastes memory and is less efficient. Remember: wrap it, then read it—the digest updates automatically with every read, so you never need to manually feed bytes to a `MessageDigest` object.
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.
A method receives an InputStream and needs to compute its MD5 hash while reading the data. Which approach is most efficient?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use DigestInputStream wrapping the original stream, then read the stream
Option A is correct because `DigestInputStream` is a built-in Java class that computes a message digest (e.g., MD5) on the fly as data is read from the underlying stream. This avoids buffering the entire stream into memory, making it both memory-efficient and CPU-efficient for large or streaming data sources.
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 DigestInputStream wrapping the original stream, then read the stream
Why this is correct
DigestInputStream computes the hash as data is read, requiring no additional memory.
Related concept
Read the scenario before looking for a memorised answer.
✗
Read all bytes into a byte array, then compute hash using MessageDigest
Why it's wrong here
Loading entire stream into memory is inefficient for large streams.
✗
Use a custom filter that hashes bytes during read
Why it's wrong here
Custom implementation is unnecessary when DigestInputStream is available.
✗
Use Scanner to read tokens and update hash
Why it's wrong here
Scanner is for parsing, not for hashing streams.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume reading all bytes into memory first (Option B) is simpler or more straightforward, overlooking the memory and performance implications for large streams, and fail to recognize that `DigestInputStream` is the standard, efficient solution in the Java I/O API.
Detailed technical explanation
How to think about this question
Under the hood, `DigestInputStream` wraps the original stream and delegates read operations to it, updating the internal `MessageDigest` object with each byte or chunk read. This streaming approach is critical for large files (e.g., gigabytes) where loading the entire content into memory is impractical. The `MessageDigest` class itself uses platform-optimized native implementations (e.g., via JCA providers) for MD5, ensuring high throughput.
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
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.
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 DigestInputStream wrapping the original stream, then read the stream — Option A is correct because `DigestInputStream` is a built-in Java class that computes a message digest (e.g., MD5) on the fly as data is read from the underlying stream. This avoids buffering the entire stream into memory, making it both memory-efficient and CPU-efficient for large or streaming data sources.
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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Question Discussion
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