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Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
public class ThisCalls {
public ThisCalls() {
this(true);
}
public ThisCalls(boolean flag) {
this();
}
}
Which statement is correct?

A) It compiles.
B) It does not compile.
C) It throws an exception at runtime.

2. How would you create a ConcurrentHashMap configured to allow a maximum of 10 concurrent writer threads and an initial capacity of 42?
Which of the following options meets this requirement?

A) None of the suggestions.
B) var concurrentHashMap = new ConcurrentHashMap();
C) var concurrentHashMap = new ConcurrentHashMap(42, 0.88f, 10);
D) var concurrentHashMap = new ConcurrentHashMap(42);
E) var concurrentHashMap = new ConcurrentHashMap(42, 10);

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

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

5. Given:
java
package vehicule.parent;
public class Car {
protected String brand = "Peugeot";
}
and
java
package vehicule.child;
import vehicule.parent.Car;
public class MiniVan extends Car {
public static void main(String[] args) {
Car car = new Car();
car.brand = "Peugeot 807";
System.out.println(car.brand);
}
}
What is printed?

A) An exception is thrown at runtime.
B) Peugeot
C) Compilation fails.
D) Peugeot 807

Solutions: