Question 372 of 509

Java I/O API and Securing Applications →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is to wrap the Files.lines call in a try-with-resources block to ensure the stream is closed automatically. This resolves the "Too many open files" error because Files.lines() opens a file handle to lazily read the stream, and without explicit closure, that handle leaks, exhausting the operating system’s file descriptor limit. In the context of the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of resource management with NIO streams—a common trap where developers assume stream operations like forEach() automatically close underlying resources. The exam emphasizes that all resources implementing AutoCloseable, including Stream from Files.lines, must be closed, typically via try-with-resources. A key memory tip: think of Files.lines as a "lazy file reader"—it holds a file handle until the stream is closed, so always pair it with try-with-resources to prevent leaks.

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. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 developer is building a batch processing application that reads a large CSV file (approx. 5 GB) from a network file system, transforms each row, and writes the result to a database. The initial implementation uses Files.lines(path) to obtain a Stream<String>, processes each line with forEach, and then does not explicitly close the stream. After running for several minutes, the application slows down, and eventually throws an IOException: 'Too many open files'. The database writes are also failing intermittently. The developer needs to fix the application. The environment is Java 17 on Linux with default settings. Which course of action best resolves the issues?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

Question 1hardmultiple choice

Read the full NAT/PAT explanation →

A
Use FileInputStream with a buffered byte array and manually scan for newline characters.
Why wrong: This is low-level, error-prone, and does not solve the resource leak issue unless the stream is also properly closed. It introduces unnecessary complexity.
B
Replace Files.lines with Files.newBufferedReader, wrapping it in a try-with-resources block.
Why wrong: This would also work but is not the best because Files.lines is more idiomatic for line-by-line streaming. However, the key issue is the missing closure; both approaches need try-with-resources. This option is plausible but not the best given that the original code used Files.lines.
C
Use Files.readAllLines to load the entire file into memory and then iterate over the list.
Why wrong: This would cause OutOfMemoryError for a 5 GB file, making the problem worse.
D
Wrap the Files.lines call in a try-with-resources block to ensure the stream is closed automatically.
By using try-with-resources, the stream's underlying file handle is closed when the block exits, fixing the resource leak. This is the minimal and correct fix.

Full breakdown with real-world context →

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

✓

Wrap the Files.lines call in a try-with-resources block to ensure the stream is closed automatically.

The 'Too many open files' error indicates that the file handle from Files.lines is not being closed, causing a resource leak. Using try-with-resources ensures the stream is closed after processing. Option A (BufferedReader) also requires try-with-resources to avoid leaks, and if not used, would have the same issue. Option C (InputStream) would not handle lines. Option D (Files.readAllLines) would cause memory issues.

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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 FileInputStream with a buffered byte array and manually scan for newline characters.
Why it's wrong here
This is low-level, error-prone, and does not solve the resource leak issue unless the stream is also properly closed. It introduces unnecessary complexity.
✗
Replace Files.lines with Files.newBufferedReader, wrapping it in a try-with-resources block.
Why it's wrong here
This would also work but is not the best because Files.lines is more idiomatic for line-by-line streaming. However, the key issue is the missing closure; both approaches need try-with-resources. This option is plausible but not the best given that the original code used Files.lines.
✗
Use Files.readAllLines to load the entire file into memory and then iterate over the list.
Why it's wrong here
This would cause OutOfMemoryError for a 5 GB file, making the problem worse.
✓
Wrap the Files.lines call in a try-with-resources block to ensure the stream is closed automatically.
Why this is correct
By using try-with-resources, the stream's underlying file handle is closed when the block exits, fixing the resource leak. This is the minimal and correct fix.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.

Common exam traps

Common exam trap: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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.

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 1Z0-829 NAT questions on configuration and troubleshooting.

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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 — Static NAT maps one inside address to one outside address..

What is the correct answer to this question?

The correct answer is: Wrap the Files.lines call in a try-with-resources block to ensure the stream is closed automatically. — The 'Too many open files' error indicates that the file handle from Files.lines is not being closed, causing a resource leak. Using try-with-resources ensures the stream is closed after processing. Option A (BufferedReader) also requires try-with-resources to avoid leaks, and if not used, would have the same issue. Option C (InputStream) would not handle lines. Option D (Files.readAllLines) would cause memory issues.

What should I do if I get this 1Z0-829 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Static NAT maps one inside address to one outside address.

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