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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
void verifyNotNull(Object input) {
boolean enabled = false;
assert enabled = true;
assert enabled;
System.out.println(input.toString());
assert input != null;
}
When does the given method throw a NullPointerException?

A) Only if assertions are enabled and the input argument is null
B) Only if assertions are disabled and the input argument is null
C) Only if assertions are enabled and the input argument isn't null
D) Only if assertions are disabled and the input argument isn't null
E) A NullPointerException is never thrown

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

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

3. Consider the following methods to load an implementation of MyService using ServiceLoader. Which of the methods are correct? (Choose all that apply)

A) MyService service = ServiceLoader.load(MyService.class).iterator().next();
B) MyService service = ServiceLoader.load(MyService.class).findFirst().get();
C) MyService service = ServiceLoader.services(MyService.class).getFirstInstance();
D) MyService service = ServiceLoader.getService(MyService.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? false; Is Car sealed? false; Is Bike sealed? false
B) Is Vehicle sealed? true; Is Car sealed? true; Is Bike sealed? true
C) Is Vehicle sealed? false; Is Car sealed? true; Is Bike sealed? true
D) Is Vehicle sealed? true; Is Car sealed? false; Is Bike sealed? false

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

Solutions: