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Oracle Java SE 21 Developer Professional Sample Questions:
1. Given:
java
List<String> abc = List.of("a", "b", "c");
abc.stream()
.forEach(x -> {
x = x.toUpperCase();
});
abc.stream()
.forEach(System.out::print);
What is the output?
A) abc
B) An exception is thrown.
C) ABC
D) Compilation fails.
2. Which of the following methods of java.util.function.Predicate aredefault methods?
A) test(T t)
B) not(Predicate<? super T> target)
C) or(Predicate<? super T> other)
D) negate()
E) isEqual(Object targetRef)
F) and(Predicate<? super T> other)
3. 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? false; Is Bike sealed? false
D) Is Vehicle sealed? true; Is Car sealed? true; Is Bike sealed? true
4. What does the following code print?
java
import java.util.stream.Stream;
public class StreamReduce {
public static void main(String[] args) {
Stream<String> stream = Stream.of("J", "a", "v", "a");
System.out.print(stream.reduce(String::concat));
}
}
A) Optional[Java]
B) Java
C) Compilation fails
D) null
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) D
B) C
C) E
D) B
E) None of the above
F) A
Solutions:
| Question # 1 Answer: A | Question # 2 Answer: C,D,F | Question # 3 Answer: C | Question # 4 Answer: A | Question # 5 Answer: E |
By Denise
