1Z0-829 Practice Test 32 — 15 Questions

Question 1

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?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Use a BufferedReader on a separate thread, reading lines into a bounded queue, and a thread pool to process rows from the queue.. 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.

Answer

Use Files.readAllLines() to read the entire file into memory, then process in parallel using streams.

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Use a FileChannel with a memory-mapped byte buffer of the entire file.

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Use a java.nio.file.FileSystem with a WatchService to detect changes to the file.

Question 2

Which two statements about multi-catch blocks are correct?

Accepted Answer

A multi-catch block can be used with a finally block.. A multi-catch block is a standard catch block that can handle multiple exception types, and it can be used with a finally block just like any other catch block. The finally block executes regardless of whether an exception is thrown or caught, and multi-catch does not alter this behavior. Option E is correct because the exception types in a multi-catch block must be disjoint, meaning they cannot be in a parent-child relationship; otherwise, the compiler would report an error due to unreachable code.

Answer

A multi-catch block cannot catch both checked and unchecked exceptions.

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The variable in a multi-catch block is not implicitly final.

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A multi-catch block can only be used with try-with-resources.

Question 3

Which statement about java.io and java.nio.file packages is true?

Accepted Answer

The java.nio.file package provides support for symbolic links and file attributes. The java.nio.file package (part of NIO.2) explicitly provides support for symbolic links via methods like Files.createSymbolicLink() and Files.isSymbolicLink(), and it offers comprehensive file attribute access through classes like BasicFileAttributes, DosFileAttributes, and PosixFileAttributes, which are not available in java.io.

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Classes in java.nio.file are thread-safe by default

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The java.io package includes the Path interface

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The java.nio.file package is deprecated in favor of java.io

Question 4

A developer is designing a method that returns an immutable list of strings from an array. Which approach best follows current Java best practices?

Accepted Answer

Return List.of(array). `List.of(array)` returns an immutable list that is null-hostile and structurally immutable, as specified by the Java Platform Module System (JPMS) and the `List` interface since Java 9. This approach aligns with current best practices by providing a concise, safe, and predictable immutable collection without the overhead of wrapping or defensive copying.

Answer

Return new ArrayList<>(Arrays.asList(array))

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Return Collections.unmodifiableList(Arrays.asList(array))

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Return Arrays.asList(array)

Question 5

A developer needs to copy a large directory tree from one location to another, preserving file attributes. Which method should be used?

Accepted Answer

Implement a FileVisitor using Files.walkFileTree and copy each file with COPY_ATTRIBUTES. `Files.walkFileTree` with a custom `FileVisitor` allows you to recursively traverse a directory tree and copy each file individually using `Files.copy` with `StandardCopyOption.COPY_ATTRIBUTES`. This is necessary because `Files.copy` on a directory does not copy the directory tree recursively; it only copies the top-level directory entry. The `FileVisitor` pattern ensures that subdirectories and files are visited and copied in depth-first order, preserving file attributes at each step.

Answer

Files.copy(source, target, StandardCopyOption.COPY_ATTRIBUTES)

Answer

Use Files.walk() and then Files.copy() for each entry

Answer

Use FileUtils.copyDirectory from Apache Commons IO

Question 6

A developer is implementing a batch processing application that reads records from a list and processes them. The method uses a for loop with an index variable. Inside the loop, if a record is null, the developer wants to skip that iteration and continue with the next index. The developer writes: for (int i = 0; i < records.size(); i++) { if (records.get(i) == null) continue; process(records.get(i)); updateCounter(); } However, the counter is not updated correctly. The developer expects the counter to reflect the number of processed (non-null) records. What is the problem?

Accepted Answer

The continue statement skips the rest of the loop body, including the counter update.. The `continue` statement immediately jumps to the next iteration of the loop, skipping any remaining code in the current iteration. In this case, `updateCounter()` is placed after the `continue` in the loop body, so when a null record is encountered, the counter update is never executed, causing the counter to not reflect the number of processed (non-null) records.

Answer

The continue statement is only valid inside a while loop.

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The continue statement should be replaced with a break.

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The counter variable should be declared as volatile.

Question 7

An application uses `--add-opens java.base/java.lang=ALL-UNNAMED` to allow reflective access to `java.lang` internals from the classpath. After migrating to a module, the flag is changed to `--add-opens java.base/java.lang=com.example.app`. Yet reflective access still fails with `InaccessibleObjectException`. What is the most likely reason?

Accepted Answer

The reflective call is made from a different module than com.example.app.. `--add-opens` specifies which module's package is opened to which target module. When the flag is changed from `ALL-UNNAMED` to `com.example.app`, only code in the `com.example.app` module is granted reflective access. If the reflective call originates from a different module (e.g., a third-party library or another application module), the `InaccessibleObjectException` will still be thrown because that module is not listed as the target.

Answer

The class performing reflection is in an unnamed module.

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The module does not read the module java.base.

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The module name in --add-opens is misspelled.

Question 8

Which interface provides the ability to store key-value pairs and allows null keys?

Accepted Answer

HashMap. HashMap is the correct answer because it implements the Map interface, allows null keys (only one null key is permitted), and does not synchronize its operations, making it suitable for unsynchronized key-value storage. In contrast, ConcurrentHashMap, TreeMap, and Hashtable all prohibit null keys for various reasons, such as thread-safety guarantees or sorting requirements.

Answer

ConcurrentHashMap

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TreeMap

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Hashtable

Question 9

A logging framework in Java has been writing logs to a file using a FileWriter with default buffer size. The logs are frequently lost when the application crashes because the buffer is not flushed. Which change ensures that log messages are written immediately without significantly impacting performance?

Accepted Answer

Use a PrintWriter wrapping a FileWriter and set autoFlush=true.. A PrintWriter wrapping a FileWriter with autoFlush=true ensures that every println, printf, or format call triggers an automatic flush of the underlying stream. This guarantees log messages are written to disk immediately upon each write, preventing data loss during a crash, while still allowing the FileWriter's internal buffer to aggregate small writes for performance. The autoFlush mechanism in PrintWriter is specifically designed for this use case in Java I/O.

Answer

Use a FileWriter with autoFlush=true.

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Set the buffer size to 0 to disable buffering.

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Call flush() after every log message.

Question 10

Which TWO statements about HashMap are true? (Select two.)

Accepted Answer

It allows null values.. HashMap allows null values; you can store null as a value for any key, including null keys. This is explicitly permitted by the HashMap specification, which does not restrict value types.

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It uses red-black trees for collision resolution.

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It guarantees insertion order.

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It is thread-safe.

Question 11

Refer to the exhibit. Which statement is true about the com.example.app.internal package?

Accepted Answer

It is accessible for deep reflection only by com.example.lib.. The exhibit shows that `com.example.app.internal` is declared with `opens com.example.app.internal to com.example.lib`. The `opens` directive grants deep reflection (access to private members) at runtime, but only to the specified module `com.example.lib`. Other modules cannot reflectively access this package unless they are explicitly listed.

Answer

It is accessible for deep reflection by any module.

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It is not accessible for reflection at all.

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It is exported to all modules.

Question 12

A Java application reads configuration from a file using FileInputStream. The application must handle the case where the configuration file is missing by logging a warning and using default values. Which design approach best meets this requirement?

Accepted Answer

Use Files.exists() to check file existence before opening the stream, and if absent, log a warning and use defaults.. It explicitly checks for file existence using `Files.exists()` before attempting to open the stream, allowing the application to log a warning and fall back to default values without throwing an exception. This approach aligns with the requirement to handle a missing configuration file gracefully, avoiding unnecessary exception handling overhead. The `Files.exists()` method is part of the modern `java.nio.file` API, which is preferred over the legacy `File.exists()` for its better integration with symbolic links and file system operations.

Answer

Wrap the FileInputStream in a try-with-resources and catch Exception to handle missing file.

Answer

Catch FileNotFoundException inside the try block and set default values.

Answer

Use File.exists() to check file existence before opening the stream, and if absent, log a warning and use defaults.

Question 13

A developer is writing a method that takes a Collection and returns a List containing the same elements in sorted order. The method should not modify the original collection. The developer tries the following code: public List sortCollection(Collection col) { return col.stream().sorted().collect(Collectors.toList()); } The code compiles and runs, but the team lead says it is not optimal. What improvement should be made?

Accepted Answer

Return an unmodifiable list using collect(Collectors.toUnmodifiableList()). The current code creates a mutable list via `Collectors.toList()`, but the method contract does not require mutability. Using `Collectors.toUnmodifiableList()` returns an unmodifiable list, which is more memory-efficient and thread-safe, and it aligns with the principle of returning immutable collections when modification is not needed. This improvement does not affect sorting correctness but optimizes the result for immutability.

Answer

Use parallelStream() for better performance

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Use a TreeSet and then convert to List

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Convert the collection to an ArrayList first, then call Collections.sort() on it