Oracle 1z0-830

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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Which of the following doesnotexist?

A) Supplier<T>
B) DoubleSupplier
C) BooleanSupplier
D) BiSupplier<T, U, R>
E) LongSupplier
F) They all exist.

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(42);
C) var concurrentHashMap = new ConcurrentHashMap(42, 0.88f, 10);
D) var concurrentHashMap = new ConcurrentHashMap();
E) var concurrentHashMap = new ConcurrentHashMap(42, 10);

3. 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.

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? 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? true; Is Bike sealed? true

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

Solutions: