1Z0-829 Practice Test 4 — 25 Questions

Question 1

Consider: List list = new LinkedList<>(); list.add(10); list.add(20); list.add(0,5); System.out.println(list); What is the output?

Accepted Answer

[5,10,20]. The code creates a LinkedList and adds 10, then 20. The third call `list.add(0,5)` inserts 5 at index 0, shifting existing elements to the right. The resulting list is [5,10,20], so option B is correct.

Answer

[10,5,20]

Answer

[10,20,5]

Answer

[5,10,20] but with type warning

Question 2

Given: TreeSet set = new TreeSet<>(List.of(3,1,2)); set.add(2); System.out.println(set); What is the output?

Accepted Answer

[1,2,3]. E is correct because TreeSet maintains elements in their natural sorted order (ascending for integers). The list [3,1,2] is sorted to [1,2,3], and adding 2 again has no effect since TreeSet does not allow duplicates. The output is [1,2,3].

Answer

[1,2]

Answer

[1,3,2]

Answer

[3,1,2]

Answer

UnsupportedOperationException

Question 3

Which of the following is a checked exception in Java?

Accepted Answer

SQLException. SQLException is a checked exception because it extends Exception directly (not RuntimeException). Checked exceptions must be either caught with a try-catch block or declared in the method signature using 'throws'. SQLException is thrown by JDBC API methods when database access errors occur, forcing the developer to handle potential SQL failures at compile time.

Answer

NullPointerException

Answer

ArrayIndexOutOfBoundsException

Answer

IllegalArgumentException

Question 4

What happens when a finally block throws an exception?

Accepted Answer

The exception from the try block is suppressed and the finally exception is reported.. When a finally block throws an exception, the JVM suppresses the exception that was thrown from the try block (if any) and propagates the exception thrown from the finally block. This behavior is defined in the Java Language Specification (JLS §14.20.2) and ensures that the finally block's exception takes precedence, as the finally block is executed after the try block completes abruptly.

Answer

The JVM logs both exceptions and then terminates the thread.

Answer

The exception from the try block is propagated and the finally exception is ignored.

Answer

Both exceptions are reported as suppressed exceptions of a new exception.

Question 5

A developer wants to ensure that a block of code always executes regardless of whether an exception occurs or not, and that any exception thrown in the block is not swallowed. Which construct should be used?

Accepted Answer

try-finally. The try-finally construct ensures that the finally block always executes after the try block, regardless of whether an exception occurs, and it does not catch or swallow any exception. This meets the requirement of guaranteed execution without suppressing the exception, as the exception propagates up the call stack.

Answer

try-catch with empty catch block

Answer

try-catch-finally with catch that rethrows the exception

Answer

try-with-resources without catch

Question 6

Which THREE statements about the SecurityManager and security policies in Java 17 are true? (Choose three.)

Accepted Answer

The SecurityManager class is deprecated in Java 17.. The SecurityManager class is deprecated for removal in Java 17 (JEP 411). This deprecation means that while the class still exists for compatibility, it is no longer recommended for use and may be removed in a future release. The core reasoning is that the SecurityManager architecture is considered legacy and difficult to maintain, so Oracle has deprecated it to encourage developers to adopt alternative security mechanisms.

Answer

System.setProperty("java.security.policy", "policy.url") loads a new policy.

Answer

By default, Java 17 applications run with a SecurityManager installed.

Question 7

A method receives an InputStream and needs to compute its MD5 hash while reading the data. Which approach is most efficient?

Accepted Answer

Use DigestInputStream wrapping the original stream, then read the stream. `DigestInputStream` is a built-in Java class that computes a message digest (e.g., MD5) on the fly as data is read from the underlying stream. This avoids buffering the entire stream into memory, making it both memory-efficient and CPU-efficient for large or streaming data sources.

Answer

Read all bytes into a byte array, then compute hash using MessageDigest

Answer

Use a custom filter that hashes bytes during read

Answer

Use Scanner to read tokens and update hash

Question 8

To generate a cryptographically secure random number for a key generation algorithm, which class should be used?

Accepted Answer

SecureRandom. D is correct because `SecureRandom` is specifically designed to produce cryptographically strong random numbers suitable for key generation, using algorithms like SHA1PRNG or NativePRNG that meet FIPS 140-2 standards. Unlike other random number generators, it ensures unpredictability and resistance to reverse engineering, which is critical for security-sensitive operations.

Answer

ThreadLocalRandom

Answer

Math.random()

Answer

Random

Question 9

Which THREE statements about the jpackage tool are true?

Accepted Answer

jpackage can create native installers for Windows, macOS, and Linux.. The jpackage tool is designed to create native installers for Windows (e.g., .exe/.msi), macOS (e.g., .dmg), and Linux (e.g., .deb/.rpm). This is a core feature of jpackage, which replaces the older Java Packager and allows developers to distribute self-contained applications with platform-specific packaging formats.

Answer

jpackage requires an existing JRE to create a runtime image.

Answer

jpackage uses the Java Packager library.

Question 10

A team is migrating a large monolithic Java 8 application to Java 17 using modules. They want to ensure that only the required packages are exported. Which tool should they use to analyze current dependencies and generate module descriptors?

Accepted Answer

jdeps. jdeps is the correct tool because it is specifically designed to analyze class dependencies in Java applications and can generate module descriptor (module-info.java) suggestions. It shows which packages are used and which are not, enabling the team to export only the required packages when migrating to Java modules.

Answer

jlink

Answer

javap

Answer

jar

Question 11

Which THREE statements about the switch statement in Java are correct?

Accepted Answer

The default case can be placed anywhere within the switch block.. The default case can be placed anywhere within the switch block according to the Java Language Specification. Option D is correct: case labels must be compile-time constant expressions; a final variable assigned a constant expression qualifies as a compile-time constant. Option E is correct: switch works with int, char, String, and enum types. Option B is incorrect because case values must be compile-time constants, not arbitrary runtime expressions. Option C is incorrect because break is not mandatory; it is optional and used to prevent fall-through.

Answer

Case values can be runtime expressions.

Answer

A break statement is mandatory after each case block.

Question 12

Which TWO statements about Java module types are true?

Accepted Answer

An automatic module exports all its packages.. The Java module system automatically exports all packages of an automatic module, making them accessible to other modules without explicit export declarations. This is a key characteristic of automatic modules, which are created from JAR files placed on the module path without a module-info.java file.

Answer

An automatic module can access all packages of named modules without explicit requires.

Answer

The unnamed module can read only the java.base module.

Answer

The unnamed module is a named module.

Question 13

A Java 17 application is packaged as a modular jar and deployed on a system with the full JDK. The application uses the java.sql module. The system administrator wants to minimize the footprint by creating a custom runtime image using jlink. Which command would create an image with only the necessary modules?

Accepted Answer

jlink --module-path $JAVA_HOME/jmods:app --add-modules com.myapp --output myimage. `jlink` with `--add-modules com.myapp` and the module path pointing to both `$JAVA_HOME/jmods` and the application JAR automatically resolves all transitive dependencies, including `java.sql`, and creates a minimal runtime image containing only the required modules. The `--output myimage` specifies the target directory for the custom image.

Answer

jlink --module-path $JAVA_HOME/jmods:app --add-modules com.myapp --bind-services --output myimage

Answer

jlink --module-path $JAVA_HOME/jmods:app --add-modules java.sql --output myimage

Answer

jlink --module-path $JAVA_HOME/jmods:app --add-modules ALL-MODULE-PATH --output myimage

Question 14

Given the following code snippet: `List list = new ArrayList<>(); list.add(10); list.add(20); list.remove(1); System.out.println(list);` What is the output?

Accepted Answer

[10]. The code creates an ArrayList, adds 10 at index 0 and 20 at index 1. Then `list.remove(1)` removes the element at index 1, which is 20. The list now contains only [10]. Option D is correct because `remove(int index)` removes the element at the specified position, not the value.

Answer

[10, 20]

Answer

[]

Answer

[20]

Question 15

Which TWO are valid uses of the 'jmod' tool in Java 17?

Accepted Answer

Listing the contents of a JMOD file.. The 'jmod' tool is primarily used for creating and inspecting JMOD files, which are a packaging format for Java modules that can include native libraries, configuration files, and other resources beyond what a modular JAR can hold. Option B is correct because 'jmod list' lists the contents of a JMOD file, showing its entries such as classes, native code, and legal notices. Option C is correct because 'jmod create' can create a JMOD file from a modular JAR and additional native libraries using the --libs option.

Answer

Creating a custom runtime image.

Answer

Executing a JMOD file as an application.

Answer

Identifying module dependencies of a jar.

Question 16

Which statement is correct about the following switch expression? String result = switch(day) { case MONDAY, TUESDAY -> "weekday"; case WEDNESDAY -> "midweek"; default -> "other"; };

Accepted Answer

The switch expression must be terminated with a semicolon.. Switch expressions in Java must be terminated with a semicolon, as they produce a value that is assigned to a variable. The given code uses the arrow syntax (->) and assigns the result to a String variable, so a semicolon is required at the end of the entire switch expression.

Answer

The switch expression is not allowed with a colon.

Answer

The default branch is optional.

Answer

The arrow operator requires a yield statement.

Question 17

Refer to the exhibit. The module path is correctly set to include the JAR containing the module. What is the most likely issue?

Accepted Answer

The Main class is not specified as the main class in the module descriptor or manifest.. When launching a modular JAR with `java -jar`, the JVM requires the main class to be explicitly declared either in the module descriptor (`module-info.java` with a `main-class` directive) or in the JAR's `MANIFEST.MF` (`Main-Class` attribute). Without this declaration, the JVM cannot determine the entry point, resulting in a 'Main class not found' error. Option A correctly identifies this missing declaration as the most likely issue.

Answer

The JAR does not have a module-info.class.

Answer

The module requires a module that is not on the module path.

Answer

The Main class is not in an exported package.

Question 18

A developer wants to create a stream that repeatedly generates random integers. Which method should be used?

Accepted Answer

IntStream.generate(() -> new Random().nextInt()). `IntStream.generate()` accepts a `Supplier<Integer>` and produces an infinite sequential unordered stream, making it ideal for repeatedly generating random integers. The lambda `() -> new Random().nextInt()` supplies a new random integer each time the stream is evaluated, fulfilling the requirement exactly.

Answer

IntStream.range(0, 100)

Answer

Stream.of(new Random().nextInt())

Answer

Stream.iterate(0, i -> new Random().nextInt())

Question 19

Given: List<String> words = List.of("apple", "banana", "cherry");
var result = words.stream().filter(s -> s.length() > 5).collect(Collectors.toUnmodifiableList());
What happens if another thread tries to add to result?

Accepted Answer

UnsupportedOperationException at runtime.. B is correct because `Collectors.toUnmodifiableList()` returns an unmodifiable list, and any attempt to modify it (e.g., via `add()`) throws an `UnsupportedOperationException`. The stream pipeline itself is safe and compiles fine; the issue is the mutability of the resulting collection.

Answer

Compilation error because var cannot be used with streams.

Answer

The thread successfully adds the element.

Answer

NullPointerException.

Question 20

Which two of the following statements are true about the continue statement in a loop?

Accepted Answer

continue can be used in a while loop.. The continue statement can be used in any loop construct in Java, including while loops. When executed, continue skips the remaining body of the loop for the current iteration and proceeds to the next iteration's condition check.

Answer

continue cannot be used in a do-while loop.

Answer

continue can be used in a switch statement.

Answer

continue can be used in a try block without a loop.