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Oracle 1z1-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
ExecutorService service = Executors.newFixedThreadPool(2);
Runnable task = () -> System.out.println("Task is complete");
service.submit(task);
service.shutdown();
service.submit(task);
What happens when executing the given code fragment?

A) It prints "Task is complete" twice and throws an exception.
B) It prints "Task is complete" once and throws an exception.
C) It prints "Task is complete" once, then exits normally.
D) It exits normally without printing anything to the console.
E) It prints "Task is complete" twice, then exits normally.

2. Given:
java
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("A");
list.add("B");
list.add("C");
// Writing in one thread
new Thread(() -> {
list.add("D");
System.out.println("Element added: D");
}).start();
// Reading in another thread
new Thread(() -> {
for (String element : list) {
System.out.println("Read element: " + element);
}
}).start();
What is printed?

A) It prints all elements, including changes made during iteration.
B) It prints all elements, but changes made during iteration may not be visible.
C) Compilation fails.
D) It throws an exception.

3. Which of the following statements is correct about a final class?

A) It cannot be extended by any other class.
B) It must contain at least a final method.
C) The final keyword in its declaration must go right before the class keyword.
D) It cannot implement any interface.
E) It cannot extend another class.

4. Given:
java
sealed class Vehicle permits Car, Bike {
}
non-sealed class Car extends Vehicle {
}
final class Bike extends Vehicle {
}
public class SealedClassTest {
public static void main(String[] args) {
Class<?> vehicleClass = Vehicle.class;
Class<?> carClass = Car.class;
Class<?> bikeClass = Bike.class;
System.out.print("Is Vehicle sealed? " + vehicleClass.isSealed() +
"; Is Car sealed? " + carClass.isSealed() +
"; Is Bike sealed? " + bikeClass.isSealed());
}
}
What is printed?

A) Is Vehicle sealed? true; Is Car sealed? true; Is Bike sealed? true
B) Is Vehicle sealed? false; Is Car sealed? true; Is Bike sealed? true
C) Is Vehicle sealed? true; Is Car sealed? false; Is Bike sealed? false
D) Is Vehicle sealed? false; Is Car sealed? false; Is Bike sealed? false

5. Given:
java
public class SpecialAddition extends Addition implements Special {
public static void main(String[] args) {
System.out.println(new SpecialAddition().add());
}
int add() {
return --foo + bar--;
}
}
class Addition {
int foo = 1;
}
interface Special {
int bar = 1;
}
What is printed?

A) 1
B) 0
C) 2
D) It throws an exception at runtime.
E) Compilation fails.

Solutions: