Java SE 21 Developer Professional Free Sample Questions

A financial application uses a sealed interface Transaction to represent various payment methods. The interface permits three record classes: CreditCard, BankTransfer, and DigitalWallet. You are writing a method to process these transactions using a switch expression with pattern matching.

public sealed interface Transaction permits CreditCard, BankTransfer, DigitalWallet {}
public record CreditCard(String pan, double amount) implements Transaction {}
public record BankTransfer(String iban, double amount) implements Transaction {}
public record DigitalWallet(String id, double amount) implements Transaction {}

// In a service class:
public String process(Transaction t) {
return switch(t) {
case CreditCard c when c.amount > 1000 -> "High Value CC";
case CreditCard c -> "Standard CC";
case BankTransfer b -> "Bank Transfer";
// Missing case
};
}

Which statement is true regarding the compilation of this code?

You are developing a high-throughput web server using Java 21's Virtual Threads. You need to protect a shared resource using a locking mechanism. However, you want to avoid 'pinning' the virtual thread to the carrier thread, which can degrade performance during blocking operations.

Which locking approach should you prefer?

Review the following code snippet that uses the new Sequenced Collections API introduced in Java 21:

import java.util.*;

public class SequenceTest {
public static void main(String[] args) {
SequencedCollection sc = new ArrayList ();
sc.addFirst("Alpha");
sc.addLast("Omega");
sc.addFirst("Beta");

System.out.println(sc.getFirst() + "-" + sc.getLast());
System.out.println(sc.reversed());
}
}

What is the output of this program?

Which of the following are valid characteristics of Java records? (Select TWO)

You are implementing a module descriptor module-info.java for a library named com.example.lib. You need to ensure that the package com.example.lib.internal is accessible via reflection to a specific testing framework module com.test.framework, but not accessible to other modules at compile time or runtime.

Which directive should you use?

Consider the following Text Block usage in Java 21:

String html = """

Hello, World

""";

If the opening """ is on line 1, and the closing """ is indented to align with the start of , how many spaces of indentation are removed from the tag line?

True or False: In Java 21, creating a Virtual Thread requires implementing a specific sub-interface of Runnable.

You need to perform a calculation using java.time.Duration. You have a start time t1 and end time t2 (both Instant). You want to calculate the number of whole days between them.

Which code snippet correctly achieves this?