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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 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) The CopyOnWriteArrayList class does not allow null elements.
D) The CopyOnWriteArrayList class is not thread-safe and does not prevent interference amongconcurrent threads.
E) Element-changing operations on iterators of CopyOnWriteArrayList, such as remove, set, and add, are supported and do not throw UnsupportedOperationException.

2. Given:
java
try (FileOutputStream fos = new FileOutputStream("t.tmp");
ObjectOutputStream oos = new ObjectOutputStream(fos)) {
fos.write("Today");
fos.writeObject("Today");
oos.write("Today");
oos.writeObject("Today");
} catch (Exception ex) {
// handle exception
}
Which statement compiles?

A) oos.write("Today");
B) fos.write("Today");
C) fos.writeObject("Today");
D) oos.writeObject("Today");

3. Given:
java
public class Versailles {
int mirrorsCount;
int gardensHectares;
void Versailles() { // n1
this.mirrorsCount = 17;
this.gardensHectares = 800;
System.out.println("Hall of Mirrors has " + mirrorsCount + " mirrors."); System.out.println("The gardens cover " + gardensHectares + " hectares.");
}
public static void main(String[] args) {
var castle = new Versailles(); // n2
}
}
What is printed?

A) Nothing
B) Compilation fails at line n2.
C) nginx
Hall of Mirrors has 17 mirrors.
The gardens cover 800 hectares.
D) Compilation fails at line n1.
E) An exception is thrown at runtime.

4. Which of the following statements are correct?

A) You can use 'private' access modifier with all kinds of classes
B) You can use 'final' modifier with all kinds of classes
C) You can use 'protected' access modifier with all kinds of classes
D) None
E) You can use 'public' access modifier with all kinds of classes

5. Given:
java
ExecutorService service = Executors.newFixedThreadPool(2);
Runnable task = () -> System.out.println("Task is complete");
service.submit(task);
service.shutdown();
service.submit(task);
What happens when executing the given code fragment?

A) It exits normally without printing anything to the console.
B) It prints "Task is complete" once, then exits normally.
C) It prints "Task is complete" once and throws an exception.
D) It prints "Task is complete" twice and throws an exception.
E) It prints "Task is complete" twice, then exits normally.

Solutions: