Oracle 1z1-830 : Java SE 21 Developer Professional

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Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
List<Integer> integers = List.of(0, 1, 2);
integers.stream()
.peek(System.out::print)
.limit(2)
.forEach(i -> {});
What is the output of the given code fragment?

A) Compilation fails
B) 012
C) An exception is thrown
D) 01
E) Nothing

2. Given:
java
Runnable task1 = () -> System.out.println("Executing Task-1");
Callable<String> task2 = () -> {
System.out.println("Executing Task-2");
return "Task-2 Finish.";
};
ExecutorService execService = Executors.newCachedThreadPool();
// INSERT CODE HERE
execService.awaitTermination(3, TimeUnit.SECONDS);
execService.shutdownNow();
Which of the following statements, inserted in the code above, printsboth:
"Executing Task-2" and "Executing Task-1"?

A) execService.run(task1);
B) execService.call(task1);
C) execService.run(task2);
D) execService.submit(task1);
E) execService.submit(task2);
F) execService.call(task2);
G) execService.execute(task2);
H) execService.execute(task1);

3. Given:
java
var sList = new CopyOnWriteArrayList<Customer>();
Which of the following statements is correct?

A) The CopyOnWriteArrayList class is a thread-safe variant of ArrayList where all mutative operations are implemented by making a fresh copy of the underlying array.
B) Element-changing operations on iterators of CopyOnWriteArrayList, such as remove, set, and add, are supported and do not throw UnsupportedOperationException.
C) The CopyOnWriteArrayList class is not thread-safe and does not prevent interference amongconcurrent threads.
D) The CopyOnWriteArrayList class's iterator reflects all additions, removals, or changes to the list since the iterator was created.
E) The CopyOnWriteArrayList class does not allow null elements.

4. Which of the following suggestions compile?(Choose two.)

A) java
sealed class Figure permits Rectangle {}
final class Rectangle extends Figure {
float length, width;
}
B) java
sealed class Figure permits Rectangle {}
public class Rectangle extends Figure {
float length, width;
}
C) java
public sealed class Figure
permits Circle, Rectangle {}
final sealed class Circle extends Figure {
float radius;
}
non-sealed class Rectangle extends Figure {
float length, width;
}
D) java
public sealed class Figure
permits Circle, Rectangle {}
final class Circle extends Figure {
float radius;
}
non-sealed class Rectangle extends Figure {
float length, width;
}

5. Given:
java
int post = 5;
int pre = 5;
int postResult = post++ + 10;
int preResult = ++pre + 10;
System.out.println("postResult: " + postResult +
", preResult: " + preResult +
", Final value of post: " + post +
", Final value of pre: " + pre);
What is printed?

A) postResult: 16, preResult: 15, Final value of post: 6, Final value of pre: 5
B) postResult: 16, preResult: 16, Final value of post: 6, Final value of pre: 6
C) postResult: 15, preResult: 16, Final value of post: 5, Final value of pre: 6
D) postResult: 15, preResult: 16, Final value of post: 6, Final value of pre: 6

Solutions: