1Z0-830 Java SE 21 Developer Professional Practice Questions

You are designing a module com.app.security that provides an implementation of a service com.app.api.Cipher. The implementation class is com.app.security.AesCipher.

Which directive in module-info.java correctly declares this provision?

What happens if a switch pattern matching block covers all possible subtypes of a sealed interface but does not include a default case?

You are using java.nio.file.Files.walk(Path start, int maxDepth, FileVisitOption... options) to traverse a directory structure. You want to ensure the traversal follows symbolic links.

Which option should you pass?

Which statement about try-with-resources is TRUE regarding the order of closing resources?

When using Math.round(double a), what is the return type?

You have a list of integers and want to use a parallel stream to compute the sum of squares.

int sum = numbers.parallelStream()
.mapToInt(i -> i * i)
.reduce(0, (a, b) -> a + b);

Is this operation thread-safe and correct?

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?