1Z0-829 Practice Test 10 — 10 Questions

Question 1

Which statement is correct about the following switch expression? String result = switch(day) { case MONDAY, TUESDAY -> "weekday"; case WEDNESDAY -> "midweek"; default -> "other"; };

Accepted Answer

The switch expression must be terminated with a semicolon.. Switch expressions in Java must be terminated with a semicolon, as they produce a value that is assigned to a variable. The given code uses the arrow syntax (->) and assigns the result to a String variable, so a semicolon is required at the end of the entire switch expression.

Answer

The switch expression is not allowed with a colon.

Answer

The default branch is optional.

Answer

The arrow operator requires a yield statement.

Question 2

Refer to the exhibit. The module path is correctly set to include the JAR containing the module. What is the most likely issue?

Accepted Answer

The Main class is not specified as the main class in the module descriptor or manifest.. When launching a modular JAR with `java -jar`, the JVM requires the main class to be explicitly declared either in the module descriptor (`module-info.java` with a `main-class` directive) or in the JAR's `MANIFEST.MF` (`Main-Class` attribute). Without this declaration, the JVM cannot determine the entry point, resulting in a 'Main class not found' error. Option A correctly identifies this missing declaration as the most likely issue.

Answer

The JAR does not have a module-info.class.

Answer

The module requires a module that is not on the module path.

Answer

The Main class is not in an exported package.

Question 3

A developer wants to create a stream that repeatedly generates random integers. Which method should be used?

Accepted Answer

IntStream.generate(() -> new Random().nextInt()). `IntStream.generate()` accepts a `Supplier<Integer>` and produces an infinite sequential unordered stream, making it ideal for repeatedly generating random integers. The lambda `() -> new Random().nextInt()` supplies a new random integer each time the stream is evaluated, fulfilling the requirement exactly.

Answer

IntStream.range(0, 100)

Answer

Stream.of(new Random().nextInt())

Answer

Stream.iterate(0, i -> new Random().nextInt())

Question 4

Given: List<String> words = List.of("apple", "banana", "cherry");
var result = words.stream().filter(s -> s.length() > 5).collect(Collectors.toUnmodifiableList());
What happens if another thread tries to add to result?

Accepted Answer

UnsupportedOperationException at runtime.. B is correct because `Collectors.toUnmodifiableList()` returns an unmodifiable list, and any attempt to modify it (e.g., via `add()`) throws an `UnsupportedOperationException`. The stream pipeline itself is safe and compiles fine; the issue is the mutability of the resulting collection.

Answer

Compilation error because var cannot be used with streams.

Answer

The thread successfully adds the element.

Answer

NullPointerException.

Question 5

Which two of the following statements are true about the continue statement in a loop?

Accepted Answer

continue can be used in a while loop.. The continue statement can be used in any loop construct in Java, including while loops. When executed, continue skips the remaining body of the loop for the current iteration and proceeds to the next iteration's condition check.

Answer

continue cannot be used in a do-while loop.

Answer

continue can be used in a switch statement.

Answer

continue can be used in a try block without a loop.

Question 6

A stream pipeline uses the peek method for debugging. Which statement about peek is correct?

Accepted Answer

peek is an intermediate operation used for debugging; it is not suitable for production side effects.. The `peek` method is an intermediate operation in the Stream API, designed primarily for debugging to observe elements as they flow through the pipeline. It is not intended for production side effects because its execution is not guaranteed for every element (e.g., due to short-circuiting or optimization), and relying on it for stateful operations can lead to unpredictable behavior.

Answer

peek is a terminal operation that prints elements.

Answer

peek can only be used with parallel streams.

Answer

peek is an intermediate operation, and it is guaranteed to be executed for each element.

Question 7

A method returns an Optional<String>. The developer wants to transform the value inside the Optional to uppercase and print it, but only if present. Which best-practice approach uses streams?

Accepted Answer

opt.stream().map(String::toUpperCase).forEach(System.out::println);. It converts the Optional to a Stream using opt.stream(), then applies map(String::toUpperCase) to transform the value, and finally uses forEach(System.out::println) to print it only if present. This approach leverages the Stream API's lazy evaluation and functional pipeline, which is the best practice for integrating Optional with streams.

Answer

opt.map(String::toUpperCase).ifPresent(System.out::println);

Answer

opt.ifPresent(s -> System.out.println(s.toUpperCase()));

Answer

Stream.of(opt).map(o -> o.get().toUpperCase()).forEach(System.out::println);

Question 8

A class `Account` has a method `public void deposit(double amount)`. Which approach correctly demonstrates method overloading?

Accepted Answer

Adding a method `public void deposit(int amount)`. Method overloading requires methods to have the same name but different parameter lists. Changing the parameter type from `double` to `int` satisfies this requirement, allowing the compiler to distinguish the methods at compile time based on the argument type.

Answer

Adding a method `public void deposit(double amount)` with different implementation

Answer

Adding a method `public int deposit(double amount)`

Answer

Adding a method `protected void deposit(double amount)`

Question 9

A developer wants to include a module in a custom runtime image using jlink. The module's `module-info.java` does not explicitly export any packages. When running the application from the custom image, a ClassNotFoundException is thrown for a class from that module. What is the most likely cause?

Accepted Answer

The module's packages are not exported, making them invisible to other modules.. If a module's `module-info.java` does not explicitly export any packages, those packages are not accessible to other modules at runtime. Even if the module is included in the custom runtime image via jlink, the `ClassNotFoundException` occurs because the class is not exported, making it invisible to other modules. The `jlink` tool includes the module's classes in the image, but without an `exports` directive, the packages remain encapsulated.

Answer

The application does not require the module.

Answer

The module uses an automatic module that is not present.

Answer

The module was not included in the jlink command.