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1Z0-830 Java SE 21 Developer Professional Sample Quiz Questions

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Disclaimer: These are sample questions created for Java 21 features. The actual exam syllabus may vary. Stay tuned to MyExamCloud for full length Practice Tests for the Java 21 Developer 1Z0-830 exam, based on the latest syllabus.

MyExamCloud 1Z0-830 Practice Tests | Java SE 21 Developer Certified Professional Mock Questions

1) What is the correct way to check if an object is an instance of a Record class called Point, and if so, print the sum of its x and y values?
Choice A:
if (obj instanceof Point(int x, int y)) {
System.out.println(x+y);
}
Choice B:
if (obj instanceof Point) {
System.out.println(x+y);
}
Choice C:
if (obj instanceof Point) {
System.out.println(obj.x+obj.y);
}
Choice D:
if (obj instanceof Point(x, y)) {
System.out.println(x+y);
}

Correct answer: Choice A
Explanation: The correct syntax for checking if an object is an instance of a record class and de-structuring its values is using the "instanceof RecordClass(parameter_1, parameter_2)" format.

2) What is the correct way to use pattern matching for switch statements to format the value of an object based on its type and return?
Choice A: case Integer i: String.format("int %d", i);
Choice B: case Integer i: String.format("int %d", i);
Choice C: case Integer i: -> return String.format("int %d", i);
Choice D: case Integer i -> return String.format("int %d", i);

Correct answer: Choice D
Explanation: The correct syntax for using pattern matching for switch statements is "case Type variable -> expression;" and it must also have a return statement to return the formatted value.

3) What is the output of the following code?
String name = "John";
String info = STR."My name is \{name}";
System.out.println(info);

Choice A: My name is John
Choice B: STR."My name is John"
Choice C: My name is {name}
Choice D: Info

Correct answer: Choice A
Explanation: Here, the "name" string is composed using the "STR" keyword followed by a string with embedded expressions. The variable "name" is used within the expression to dynamically generate the string "My name is John".

4) Which symbol can be used to elide unnecessary nested patterns and variables in an if statement?
Choice A: :
Choice B: .
Choice C: _
Choice D: /

Correct answer: Choice C
Explanation: The underscore "_" character can be used to identify unnecessary nested patterns and variables in Java as part of the Unnamed Patterns and Variables feature.

For example:

if (r instanceof ColoredPoint(Point(int x, _), _)) {
  ... x ...
}


Here, the unnecessary "y" value and "c" color are eliminated, making the code more concise and easier to read.

5) What is the correct syntax for referencing the first element of a sequenced collection called "list"?
Choice A: list.get(first)
Choice B: list.getFirst()
Choice C: list.element(0)
Choice D: list.get(0)

Correct answer: Choice D
Explanation: The correct syntax for accessing elements in a sequenced collection is "collection.get(index)".

6) What is the output of the following code?
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
  IntStream.range(0, 10 _000).forEach(i -> {
    executor.submit(() -> {
      Thread.sleep(Duration.ofSeconds(1));
      return i;
    });
  });
} // executor.close() is called implicitly, and waits

Choice A: 10_000
Choice B: 9_999
Choice C: An error will occur
Choice D: 0

Correct answer: Choice A
Explanation: The code will submit 10,000 tasks to the executor, each with a sleep time of 1 second. The tasks will be executed in parallel and the loop will end. The executor will be closed implicitly, but will wait for all tasks to finish before closing.

7) What is the purpose of using the Structured Concurrency API?
Choice A: To enable safe and efficient sharing of immutable data within threads
Choice B: To structure a task as a family of concurrent subtasks and coordinate them as a unit
Choice C: To reduce syntactic complexity of simple programs
Choice D: To enhance the collections framework with new interfaces for sequenced collections

Correct answer: Choice B
Explanation: The Structured Concurrency API is used to structure tasks as a family of concurrent subtasks and to coordinate them as a unit, providing structure for large numbers of virtual threads.

8) What is the correct syntax for creating a ScopedValue object called "NAME"?
Choice A: ScopedValue<...> NAME = ScopedValue.newInstance();
Choice B: ScopedValue<NAME> NAME = ScopedValue.newInstance();
Choice C: ScopedValue NAME = ScopedValue.getInstance("NAME");
Choice D: ScopedValue.newInstance("NAME");

Correct answer: Choice A
Explanation: The correct syntax for creating a ScopedValue object is " ScopedValue<...> NAME = ScopedValue.newInstance();".

9) What is the purpose of the Foreign Function & Memory API?
Choice A: To enable Java programs to call native libraries and process native data
Choice B: To provide a safer alternative to JNI
Choice C: To allow for simplified string interpolation
Choice D: To enable lightweight threads to reduce effort in concurrent applications

Correct answer: Choice A
Explanation: The Foreign Function & Memory API enables Java programs to call native libraries and process native data without the risk and complexity of using JNI.

10) What is the purpose of using the Linker object in the Foreign Function & Memory API?
Choice A: To allocate memory for the native library
Choice B: To find and execute methods from the native library
Choice C: To provide a way to call foreign functions
Choice D: To create a new instance for using the Foreign Function & Memory API

Correct answer: Choice C
Explanation: The Linker object in the Foreign Function & Memory API is used to call foreign functions, specifically to create a "downcallHandle" for the library's methods.

11) What is the correct syntax for joining subtasks within a StructuredTaskScope object named scope?
Choice A: scope.fork(subtask);
Choice B: scope.join(struct, subtask);
Choice C: scope.join(subtask);
Choice D: subtask.join(scope);

Correct answer: Choice C
Explanation: The correct syntax for joining subtasks within a StructuredTaskScope object is "scope.join(subtask)" as the join method belongs to the scope, not the subtask.

12) What is the output of the following code?
try (var arena = Arena.ofConfined()) {
  MemorySegment segment = arena.allocate(ValueLayout.BOOLEAN);
  System.out.println(segment.byteAt(0));
}
Choice A: 0
Choice B: 1
Choice C: MemorySegment
Choice D: An error will occur

Correct answer: Choice A
Explanation: The code will allocate a MemorySegment with the size of a boolean, which is 1 byte. The byteAt() method is used to access the first byte of the segment, which is initialized as the default value of a boolean, 0.

13) What is the output of the following code?
try (var allocator = Allocator.allocate(Arena.class)) {
  Allocator allocator = allocatorChecker.getAllocator();
  System.out.println(allocator);
}
Choice A: Error
Choice B: Allocator
Choice C: ClassCastException
Choice D: Null

Correct answer: C
Explanation: The code will throw a ClassCastException as the "allocator" variable is trying to be reassigned as an Allocator object instead of an Arena object.

14) What is the purpose of using the Executors.newVirtualThreadPerTaskExecutor() method?
Choice A: To create a new virtual thread for each task submitted to the executor
Choice B: To clean up and close the executor after all tasks have completed
Choice C: To allocate memory for the new virtual threads
Choice D: To ensure that all tasks are executed sequentially

Correct answer: Choice A
Explanation: The Executors.newVirtualThreadPerTaskExecutor() method is used to create a new virtual thread for each task submitted to the executor and return an Executor object to manage those tasks.

15) What is the output of the following code?
ScopedValue.runWhere(NAME, "duke", () -> { ... NAME.get() ... call methods ... });
Choice A: duke
Choice B: getName()
Choice C: SCE.XPATH.get()
Choice D: An error will occur

Correct answer: Choice A
Explanation: The code will print "duke" as a ScopedValue object named "NAME" was created and set to the value of "duke" within the lambda expression.

16) What is the correct syntax for assigning the first element of a LinkedHashSet called "linkedHashSet" to a variable called "first"?
Choice A: first = linkedHashSet.first;
Choice B: first = linkedHashSet.element(0);
Choice C: first = linkedHashSet.getFirst();
Choice D: first = linkedHashSet.iterator.next();

Correct answer: Choice D
Explanation: The correct syntax for assigning the first element of a LinkedHashSet to a variable is "linkedHashSet.iterator.next()". The iterator is used to traverse through the set and the next() method is used to access the next element, in this case the first element.

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