1Z0-829 Practice Test 4 — 10 Questions

Question 1

A class implements Serializable. Which modification ensures that a specific field (password) is not included in the serialized stream?

Accepted Answer

Declare the field as transient. The `transient` modifier is the correct mechanism in Java to exclude a specific field from the default serialization process. When a class implements `Serializable`, all non-transient instance fields are serialized by default. Marking the `password` field as `transient` ensures it is skipped during serialization and restored as `null` (or default value) upon deserialization.

Answer

Declare the field as volatile

Answer

Declare the field as static

Answer

Declare the field as final

Question 2

Which interface is designed for recursively walking a file tree?

Accepted Answer

FileVisitor [CORRECT]. The `FileVisitor` interface is designed for recursively walking a file tree, as it provides callback methods (`preVisitDirectory`, `postVisitDirectory`, `visitFile`, `visitFileFailed`) that are invoked during a depth-first traversal of a file tree, typically used with `Files.walkFileTree()`. This allows you to process each file and directory in the tree, including subdirectories, making it the correct choice for recursive file tree walking.

Answer

DirectoryStream [wrong]

Answer

FilenameFilter [wrong]

Answer

FileFilter [wrong]

Question 3

Given: ZonedDateTime zdt = ZonedDateTime.of(2024, 3, 10, 2, 30, 0, 0, ZoneId.of("America/New_York")); In the US, on March 10, 2024, clocks spring forward at 2:00 AM to 3:00 AM. What is the output of System.out.println(zdt);?

Accepted Answer

2024-03-10T03:30-04:00[America/New_York]. When a ZonedDateTime is created for a time that falls within a DST gap (2:00 AM to 3:00 AM on March 10, 2024, in America/New_York), the Java API automatically adjusts the time forward to the next valid offset. The local time 2:30 AM does not exist because clocks spring forward to 3:00 AM, so the ZonedDateTime is normalized to 3:30 AM with the DST offset -04:00. This behavior is defined by the ZonedDateTime.of method, which resolves invalid local times by shifting to the offset after the gap.

Answer

Throws DateTimeException

Answer

2024-03-10T02:30-05:00[America/New_York]

Answer

2024-03-10T02:30-04:00[America/New_York]

Question 4

Given a requirement to efficiently copy a large file (over 2 GB) from one path to another, which approach is most appropriate for Java NIO.2?

Accepted Answer

Using FileChannel.transferTo() with position and count. `FileChannel.transferTo()` leverages zero-copy I/O, which allows data to be transferred directly between file system caches without unnecessary copying through user-space buffers. This is particularly efficient for large files (over 2 GB) as it minimizes context switches and memory overhead, and the method supports a `position` and `count` parameter to handle large file offsets correctly.

Answer

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

Answer

Using Files.readAllBytes() then Files.write()

Answer

Using FileInputStream and FileOutputStream with a buffer of 8192 bytes

Question 5

Which TWO of the following are checked exceptions in Java?

Accepted Answer

SQLException. A is correct because `SQLException` is a subclass of `java.lang.Exception` (which is a checked exception class) and does not extend `RuntimeException`. Checked exceptions must be either caught or declared in the method signature; `SQLException` is commonly thrown when database access errors occur, such as connection failures or SQL syntax errors.

Answer

ArithmeticException

Answer

ArrayIndexOutOfBoundsException

Answer

NullPointerException

Question 6

A serialized object has an explicitly declared serialVersionUID of 123L. After a code change, a new field is added to the class but the serialVersionUID is left unchanged. What happens when deserializing an old stream?

Accepted Answer

Deserialization succeeds and the new field is set to its default value.. When a serialized object has an unchanged serialVersionUID, the Java deserialization mechanism treats the class as compatible. The new field is not present in the old stream, so it is simply initialized to its default value (e.g., null for objects, 0 for primitives) without throwing an exception. This behavior is defined by the Java Object Serialization Specification, which allows forward compatibility as long as the serialVersionUID matches.

Answer

Deserialization succeeds only if the new field is marked transient.

Answer

Deserialization throws StreamCorruptedException due to missing field.

Answer

Deserialization throws InvalidClassException because the class definition has changed.

Question 7

Which resource declaration order in try-with-resources is valid when both a FileInputStream and a BufferedInputStream wrapping it need to be closed automatically?

Accepted Answer

try (FileInputStream fis = new FileInputStream("a"); BufferedInputStream bis = new BufferedInputStream(fis)) { ... }. In a try-with-resources statement, resources are declared in order and closed in reverse order. By declaring FileInputStream first and then BufferedInputStream wrapping it, both resources are properly closed automatically, with the BufferedInputStream closed first (ensuring its buffer is flushed) and then the FileInputStream.

Answer

try (FileInputStream fis = new FileInputStream("a")) { BufferedInputStream bis = new BufferedInputStream(fis); ... }

Answer

try (BufferedInputStream bis = new BufferedInputStream(fis); FileInputStream fis = new FileInputStream("a")) { ... }

Answer

try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream("a"))) { ... }

Question 8

A developer is tasked with reading a large binary file (1 GB) from a network share using the least amount of memory possible. Which approach should be used?

Accepted Answer

Use a FileInputStream wrapped in a BufferedInputStream with a 8 KB buffer. Using a FileInputStream wrapped in a BufferedInputStream with a small buffer (e.g., 8 KB) allows reading the file in chunks without loading the entire 1 GB into memory. This approach minimizes heap usage by processing data incrementally, which is essential for large binary files over a network share where memory constraints are critical.

Answer

Read the entire file into a byte array using Files.readAllBytes()

Answer

Use a FileReader wrapped in a BufferedReader to read lines

Answer

Use a RandomAccessFile to read the file in segments

Question 9

How many times does the following loop execute? int i=0; while(i<5) { System.out.println(i); i++; }

Accepted Answer

5. The loop starts with i=0, checks the condition i<5 (true), prints i, then increments i. This repeats until i becomes 5, at which point i<5 is false and the loop terminates. Thus, the loop executes exactly 5 times (i=0,1,2,3,4).

Answer

0

Answer

6

Answer

4