1Z0-830 sample questions

Question 1

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.

```java
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?

Accepted Answer

It fails to compile because the switch expression is not exhaustive.

Answer

It compiles successfully because `DigitalWallet` is not required.

Answer

It fails to compile because the `when` guard is not supported in Java 21.

Answer

It compiles successfully, and `DigitalWallet` transactions return null implicitly.

Question 2

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?

Accepted Answer

Use `java.util.concurrent.locks.ReentrantLock`.

Answer

Use the `synchronized` keyword on the method or block.

Answer

Use `Thread.yield()` inside a spin-lock loop.

Answer

Use `Object.wait()` and `Object.notify()`.

Question 3

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

```java
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?

Accepted Answer

Beta-Omega
[Omega, Alpha, Beta]

Answer

Alpha-Omega
[Omega, Alpha, Beta]

Answer

Beta-Omega
[Beta, Alpha, Omega]

Answer

Alpha-Beta
[Omega, Beta, Alpha]

Question 4

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

Accepted Answer

Records are implicitly final and cannot be abstract.

Accepted Answer

Records can implement interfaces.

Answer

Records can extend other classes.

Answer

Records cannot contain static fields or methods.

Answer

Record components are mutable by default.

Question 5

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?

Accepted Answer

opens com.example.lib.internal to com.test.framework;

Answer

exports com.example.lib.internal to com.test.framework;

Answer

requires transitive com.test.framework;

Answer

uses com.example.lib.internal;

Question 6

Consider the following Text Block usage in Java 21:

```java
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?

Accepted Answer

The number of spaces equal to the indentation of the closing delimiter.

Answer

All indentation is preserved.

Answer

The number of spaces equal to the indentation of the first line of content.

Answer

4 spaces are always removed by standard convention.

Question 7

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

Accepted Answer

False

Answer

True

Question 8

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?

Accepted Answer

long days = Duration.between(t1, t2).toDays();

Answer

long days = Period.between(t1, t2).getDays();

Answer

long days = ChronoUnit.DAYS.between(t1, t2);

Answer

long days = (t2.getEpochSecond() - t1.getEpochSecond()) / 86400;

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Free 1Z0-830 sample questions

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

Consider the following Text Block usage in Java 21: ```java 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?

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