1Z0-829 Practice Test 21 — 15 Questions

Question 1

A stream pipeline uses sorted() with a Comparator that calls a thread-unsafe method on each element. The pipeline is parallel. What is the likely outcome?

Accepted Answer

The pipeline may produce incorrect ordering or throw a ConcurrentModificationException.. In a parallel stream pipeline, the `sorted()` operation requires a stable sort that merges results from multiple threads. If the provided `Comparator` calls a thread-unsafe method on each element, concurrent invocations from different threads can cause race conditions, leading to incorrect ordering or a `ConcurrentModificationException` if the method modifies shared state. The pipeline does not automatically fall back to sequential execution for `sorted()` when the comparator is stateful or unsafe.

Answer

The pipeline will throw an exception because the comparator is stateful.

Answer

The pipeline will sort correctly because sorted() is a sequential operation.

Answer

The pipeline will run sequentially because the stream source is not ordered.

Question 2

A company uses CI/CD to build and package a Java 17 application. They want to produce a single executable JAR that includes all dependencies. Which tool should be used to achieve this?

Accepted Answer

Maven Shade Plugin. The Maven Shade Plugin (B) is the correct choice because it creates an uber-JAR (fat JAR) by merging all project dependencies into a single executable JAR, including transitive dependencies. It also provides a relocation feature to avoid classpath conflicts, which is essential for producing a self-contained artifact for deployment.

Answer

Maven JAR Plugin

Answer

Java jar command

Answer

jlink tool

Question 3

A financial trading application is developed using Java 17 and the Java Platform Module System (JPMS). The application consists of 50 named modules, including third-party libraries that are automatic modules. The team uses jlink to create a custom runtime image for deployment on customer servers. They observe that the jlink process takes over 10 minutes and produces an image of 200 MB. They want to reduce both the build time and the image size. Which action would be most effective?

Accepted Answer

Use the --limit-modules option to restrict jlink to only the application's root modules.. The --limit-modules option restricts jlink to only the specified root modules and their transitive dependencies, pruning unnecessary modules from the analysis and image. This directly reduces the number of modules jlink must process, cutting build time, and eliminates unused module classes from the runtime image, shrinking its size. In contrast, options like --strip-java-debug-attributes or --compress=2 only reduce image size after all modules are included, without addressing the root cause of excessive module scanning.

Answer

Replace jlink with jpackage to create a platform-specific installer.

Answer

Use the --strip-java-debug-attributes option to remove debug information.

Answer

Add the --compress=2 option to the jlink command.

Question 4

Which THREE are recommended practices to prevent privilege escalation when using doPrivileged in a security-sensitive Java application?

Accepted Answer

Restrict the codebase URLs in policy files to only trusted code locations.. Restricting codebase URLs in policy files to only trusted code locations limits the sources from which privileged code can be loaded. This prevents an attacker from injecting malicious code from an untrusted URL that could otherwise be granted elevated permissions via doPrivileged. By narrowing the codebase, you reduce the attack surface for privilege escalation attacks.

Answer

Use SubjectDomainCombiner to merge multiple protection domains.

Answer

Always use a SecurityManager to enforce the policy.

Question 5

Examine the code: List list = new ArrayList<>(); list.add("A"); list.add("B"); for (String s : list) { list.remove(s); } What is the outcome?

Accepted Answer

A ConcurrentModificationException is thrown. The for-each loop internally uses an Iterator to traverse the list. When the list is structurally modified (via `list.remove()`) during iteration without using the iterator's own `remove()` method, the iterator detects a concurrent modification and throws a `ConcurrentModificationException`. This is a fail-fast behavior of the `ArrayList` iterator.

Answer

The loop completes successfully and list becomes empty

Answer

An IllegalStateException is thrown

Answer

The loop completes successfully and list contains [B]

Question 6

Refer to the exhibit. What is the result of compiling and running the Test class?

Accepted Answer

Compilation error at line 9 because Vehicle does not have a drive() method.. The reference type of the variable `v` is `Vehicle`, and the `Vehicle` interface does not declare a `drive()` method. Since the compiler checks the reference type for method availability, calling `v.drive()` results in a compilation error, even though the actual object is a `Car` that has a `drive()` method.

Answer

Runtime exception because drive() is not accessible.

Answer

Prints "Car engine started" followed by "Car is moving".

Answer

Compilation error because Car does not implement all abstract methods.

Question 7

Which TWO of the following are valid forms of the switch statement/expression in Java?

Accepted Answer

switch(x) { case 1: System.out.println("one"); break; }. It uses the traditional switch statement syntax with a colon after the case label, a statement to execute, and a break statement to prevent fall-through. This is a valid and long-standing form of the switch statement in Java.

Answer

switch(x) { case 1 -> "one"; }

Answer

String r = switch(x) { case 1: break "one"; };

Answer

switch(x) { case 1: yield "one"; }

Question 8

A developer needs to write text to a file with UTF-8 encoding. Which class should be used?

Accepted Answer

new OutputStreamWriter(new FileOutputStream(file), StandardCharsets.UTF_8). It explicitly constructs an OutputStreamWriter with a FileOutputStream and StandardCharsets.UTF_8, ensuring the text is written with UTF-8 encoding. This is the standard approach when you need precise control over the character encoding, as the OutputStreamWriter acts as a bridge from byte streams to character streams using the specified charset.

Answer

BufferedWriter

Answer

FileWriter

Answer

PrintWriter with default constructor

Question 9

A TreeSet<String> is used to store a list of employee names. The set currently contains "Alice", "Bob", "Charlie". What is the output after calling set.add("Bob")?

Accepted Answer

false. A TreeSet implements the Set interface, which does not allow duplicate elements. When calling add("Bob") on a TreeSet that already contains "Bob", the add method returns false, indicating that the element was not added, and the set remains unchanged.

Answer

Exception

Answer

The set becomes ["Alice","Bob","Bob","Charlie"]

Answer

true

Question 10

A developer runs the above jdeps command on app.jar. Which statement about the dependencies is correct?

Accepted Answer

The app.jar depends on java.base implicitly.. Every Java module automatically has an implicit dependency on the `java.base` module, which is always resolved by the module system. The `jdeps` command analyzes dependencies, and even if no explicit `requires java.base` is declared, the module system adds it implicitly. This is a fundamental rule of the Java Platform Module System (JPMS) as defined in JSR 376.

Answer

The app.jar has a direct dependency on the class com.thirdparty.util.

Answer

The modular dependency com.thirdparty.helper is not required because it is modular.

Answer

The dependencies on com.thirdparty.util and com.thirdparty.helper are on the module path.

Question 11

Which TWO statements are true about ArrayList in Java 17? (Choose two.)

Accepted Answer

It implements the List interface. ArrayList implements the List interface, which is a core part of the Java Collections Framework. This allows ArrayList to be used polymorphically wherever a List is expected, providing ordered, index-based access to elements.

Answer

It implements the Set interface

Answer

It implements the Queue interface

Answer

It is synchronized

Question 12

Which two statements are true about FileInputStream? (Select two.)

Accepted Answer

It extends java.io.InputStream.. FileInputStream directly extends java.io.InputStream, inheriting its abstract methods for reading bytes from a file. Option C is correct because FileInputStream implements java.io.Closeable, which extends AutoCloseable, allowing it to be used in try-with-resources statements for automatic resource management.

Answer

It supports mark() and reset().

Answer

It reads data in big-endian order.

Answer

It can be used to read characters.

Question 13

Refer to the exhibit. What is the result of compiling and running the Main class?

Accepted Answer

Compilation error at line 8 because makeSound() has protected access.. The `makeSound()` method in the `Animal` class has `protected` access, and the `Dog` class is in a different package. In Java, a `protected` member is accessible only within the same package or through inheritance in a subclass, but only if the access is via a reference of the subclass type. In the `Main` class, the reference is of type `Animal` (line 8), not `Dog`, so the compiler cannot access the `protected` method from a different package, resulting in a compilation error.

Answer

Runtime exception because makeSound() is not accessible.

Answer

Compilation error because Dog does not override makeSound().

Answer

Prints "Some sound".

Question 14

Refer to the exhibit. What is the output?

Accepted Answer

Class implementation. When a class implements an interface that provides a default method, the class can override that default method with its own implementation. In this case, the class provides a concrete implementation of the `show()` method, which takes precedence over the interface's default method. Therefore, the output is 'Class implementation'.

Answer

Runtime exception due to conflicting methods.

Answer

Compilation error because show() is default in interface and cannot be overridden.

Answer

Interface default