Oracle 1z1-830 : Java SE 21 Developer Professional

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Oracle 1z1-830 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 is a thread-safe variant of ArrayList where all mutative operations are implemented by making a fresh copy of the underlying array.
C) The CopyOnWriteArrayList class does not allow null elements.
D) Element-changing operations on iterators of CopyOnWriteArrayList, such as remove, set, and add, are supported and do not throw UnsupportedOperationException.
E) The CopyOnWriteArrayList class is not thread-safe and does not prevent interference amongconcurrent threads.

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

3. 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) var concurrentHashMap = new ConcurrentHashMap(42);
B) var concurrentHashMap = new ConcurrentHashMap(42, 10);
C) var concurrentHashMap = new ConcurrentHashMap();
D) var concurrentHashMap = new ConcurrentHashMap(42, 0.88f, 10);
E) None of the suggestions.

4. Given:
java
var frenchCities = new TreeSet<String>();
frenchCities.add("Paris");
frenchCities.add("Marseille");
frenchCities.add("Lyon");
frenchCities.add("Lille");
frenchCities.add("Toulouse");
System.out.println(frenchCities.headSet("Marseille"));
What will be printed?

A) [Lille, Lyon]
B) Compilation fails
C) [Paris]
D) [Lyon, Lille, Toulouse]
E) [Paris, Toulouse]

5. Which methods compile?

A) ```java
public List<? extends IOException> getListExtends() {
return new ArrayList<FileNotFoundException>();
}
B) ```java public List<? extends IOException> getListExtends() { return new ArrayList<Exception>(); } csharp
C) ```java public List<? super IOException> getListSuper() { return new ArrayList<Exception>(); } csharp
D) ```java
public List<? super IOException> getListSuper() {
return new ArrayList<FileNotFoundException>();
}

Solutions: