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Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
interface A {
default void ma() {
}
}
interface B extends A {
static void mb() {
}
}
interface C extends B {
void ma();
void mc();
}
interface D extends C {
void md();
}
interface E extends D {
default void ma() {
}
default void mb() {
}
default void mc() {
}
}
Which interface can be the target of a lambda expression?

A) B
B) D
C) None of the above
D) A
E) C
F) E

2. Given:
java
Optional<String> optionalName = Optional.ofNullable(null);
String bread = optionalName.orElse("Baguette");
System.out.print("bread:" + bread);
String dish = optionalName.orElseGet(() -> "Frog legs");
System.out.print(", dish:" + dish);
try {
String cheese = optionalName.orElseThrow(() -> new Exception());
System.out.println(", cheese:" + cheese);
} catch (Exception exc) {
System.out.println(", no cheese.");
}
What is printed?

A) Compilation fails.
B) bread:bread, dish:dish, cheese.
C) bread:Baguette, dish:Frog legs, cheese.
D) bread:Baguette, dish:Frog legs, no cheese.

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) The CopyOnWriteArrayList class is not thread-safe and does not prevent interference amongconcurrent threads.
C) The CopyOnWriteArrayList class's iterator reflects all additions, removals, or changes to the list since the iterator was created.
D) The CopyOnWriteArrayList class does not allow null elements.
E) Element-changing operations on iterators of CopyOnWriteArrayList, such as remove, set, and add, are supported and do not throw UnsupportedOperationException.

4. Which methods compile?

A) ```java
public List<? super IOException> getListSuper() {
return new ArrayList<FileNotFoundException>();
}
B) ```java
public List<? extends IOException> getListExtends() {
return new ArrayList<FileNotFoundException>();
}
C) ```java public List<? extends IOException> getListExtends() { return new ArrayList<Exception>(); } csharp
D) ```java public List<? super IOException> getListSuper() { return new ArrayList<Exception>(); } csharp

5. 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? false; 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? true; Is Car sealed? false; Is Bike sealed? false

Solutions: