1Z0-829 Practice Test 1 — 10 Questions

Question 1

A financial application uses Java SE 17 with a custom date format. The requirement is to parse strings like "2023-12-31T23:59:59.999Z" into an Instant. The existing code uses SimpleDateFormat with pattern "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'" and then calls parse(). It works fine in single-threaded testing, but in production under load, intermittent parsing failures occur with DateTimeParseException or wrong values. The application is multi-threaded and reuses the same formatter instance. Which single change should be made to fix the issue while maintaining performance?

Accepted Answer

Replace SimpleDateFormat with DateTimeFormatter.ISO_INSTANT and use Instant.from(). Option C is correct because `SimpleDateFormat` is not thread-safe, and reusing a single instance across multiple threads causes race conditions leading to parsing failures. Replacing it with `DateTimeFormatter.ISO_INSTANT` (which is immutable and thread-safe) and using `Instant.from()` directly parses the ISO 8601 string without any synchronization overhead, maintaining performance while fixing the concurrency bug.

Answer

Wrap the parse call in a synchronized block

Answer

Use a ThreadLocal<SimpleDateFormat> to give each thread its own instance

Answer

Create a new SimpleDateFormat instance for each parse call

Question 2

Which TWO statements about the switch statement in Java are correct?

Accepted Answer

The default case can be placed anywhere within the switch block.. Option A is correct because the Java Language Specification allows the default case to appear anywhere within the switch block, not just at the end. The switch statement evaluates the expression and jumps to the matching case label; if no match is found, it jumps to the default label regardless of its position. This flexibility is important for code organization and readability.

Answer

Case values can be runtime expressions.

Answer

A break statement is mandatory after each case block.

Answer

Case labels can be variables if they are final and assigned a constant expression.

Question 3

Which THREE statements are true about the java.util.Collection and java.util.stream.Stream APIs? (Choose three.)

Accepted Answer

The Stream.forEach() operation processes elements in the encounter order of the stream only for sequential streams.. Option B is correct because the Stream.forEach() operation respects the encounter order of the stream only for sequential streams. For parallel streams, the order is not guaranteed unless the stream is explicitly forced to be sequential or uses forEachOrdered(). This behavior is defined in the Stream API specification.

Answer

The Collection.forEach() method is inherited from the Collection interface.

Answer

The Collection interface inherits the stream() method from the Iterable interface.

Question 4

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 5

A developer is implementing a custom sort for a list of Employee objects. The Employee class has fields: String name, int age. The list must be sorted first by name (ascending, case-insensitive), then by age (descending). Which Comparator implementation correctly achieves this?

Accepted Answer

Comparator.comparing(Employee::getName, String.CASE_INSENSITIVE_ORDER).thenComparing(Comparator.comparingInt(Employee::getAge).reversed()). Option B is correct because it first sorts by name using a case-insensitive comparator, then chains a reversed comparator for age, ensuring descending order for age while preserving the primary sort by name. The `thenComparing` method correctly applies the reversed age comparator as a secondary sort, which is essential for multi-field sorting where one field requires descending order.

Answer

Comparator.comparing(Employee::getName, String.CASE_INSENSITIVE_ORDER).thenComparingInt(Employee::getAge)

Answer

Comparator.comparingInt(Employee::getAge).reversed().thenComparing(Employee::getName, String.CASE_INSENSITIVE_ORDER)

Answer

Comparator.comparing(Employee::getName).thenComparingInt(Employee::getAge).reversed()

Question 6

What is the result of executing the code in the exhibit?

Accepted Answer

ConcurrentModificationException is thrown.. The code uses an ArrayList and iterates over it with an enhanced for-each loop while simultaneously removing an element via the list's remove() method. This structural modification directly from the list (not via the iterator's remove()) triggers a ConcurrentModificationException because the iterator's modCount check fails. The exception is thrown at the next iteration attempt after the removal.

Answer

The code compiles and runs without output.

Answer

[A, C]

Answer

[A, B]

Question 7

Which TWO statements are true about the Java Platform Module System (JPMS) introduced in Java 9?

Accepted Answer

The module declaration is stored in a file named module-info.java.. Option B is correct because the module declaration in JPMS is indeed stored in a file named module-info.java, which is compiled into module-info.class and placed at the root of the module. This file defines the module's name, dependencies (requires), and exported packages (exports).

Answer

The module path is searched after the class path when resolving types.

Answer

An automatic module is one that has a module-info.class file at its root.

Answer

A named module can access the unnamed module without any explicit declaration.

Question 8

A developer wants to find the longest word in a list of strings. Which stream operation should be used?

Accepted Answer

stream().max(Comparator.comparingInt(String::length)). Option D is correct because the `max()` terminal operation, when combined with a `Comparator` that compares strings by their length, returns the longest word in the stream. The `max()` operation uses the provided comparator to determine the 'largest' element according to the ordering, which in this case is the string with the greatest length.

Answer

stream().sorted(Comparator.comparingInt(String::length).reversed()).findFirst()

Answer

stream().min(Comparator.comparingInt(String::length))

Answer

stream().sorted(Comparator.comparingInt(String::length)).findFirst()

Question 9

A Java 17 application is deployed on a server. The application uses modules but one required module is missing from the module path. Which exception will be thrown at startup?

Accepted Answer

ModuleNotFoundException. Option D is correct because when a required module is missing from the module path in Java 17, the module system throws `ModuleNotFoundException` during the resolution phase at startup. This exception is specific to the Java Platform Module System (JPMS) and indicates that a module declared in `requires` clauses cannot be located.

Answer

ExceptionInInitializerError

Answer

NoClassDefFoundError

Answer

ClassNotFoundException