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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
var sList = new CopyOnWriteArrayList<Customer>();
Which of the following statements is correct?

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

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

3. Given:
java
StringBuilder result = Stream.of("a", "b")
.collect(
() -> new StringBuilder("c"),
StringBuilder::append,
(a, b) -> b.append(a)
);
System.out.println(result);
What is the output of the given code fragment?

A) bca
B) abc
C) cacb
D) acb
E) bac
F) cbca
G) cba

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

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

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

Solutions: