1Z0-829 Java Platform Overview and Packaging Practice Test 2 — 15 Questions

Question 1

A development team is working on a Java 17 application that must be packaged as a custom runtime image for deployment on a Linux server without a JDK installed. The application uses `java.base`, `java.logging`, and `java.sql` modules, and also requires the `jdk.crypto.cryptoki` module for hardware security module (HSM) integration. The team wants to minimize the image size while ensuring all necessary modules are included. They run `jlink --add-modules java.base,java.logging,java.sql,jdk.crypto.cryptoki --output myapp-runtime`. The resulting image runs the application but fails at startup with a `ClassNotFoundException` for `javax.crypto.spec.SecretKeySpec`. Which action should the team take to resolve the issue?

Accepted Answer

Add `--bind-services` to the jlink command to include service provider modules.. The `jdk.crypto.cryptoki` module is a service provider module that provides cryptographic services via the Java Cryptography Architecture (JCA). When using `jlink`, service provider modules are not automatically included unless `--bind-services` is specified, because `jlink` only includes modules directly referenced in the module graph. The `javax.crypto.spec.SecretKeySpec` class is part of `java.base`, but the actual provider implementation that makes it available at runtime is in `jdk.crypto.cryptoki`; without `--bind-services`, the service linkage is missing, causing the `ClassNotFoundException`.

Answer

Manually add the `java.security.jgss` module to the `--add-modules` list.

Answer

Use the `--list-modules` option with jlink to verify which modules are included, then add any missing ones.

Answer

Add `ALL-MODULE-PATH` to the `--add-modules` list to include all available modules.

Question 2

Arrange the steps to read a file using NIO.2 Files.lines() in Java.

Question 3

Match each Java 17 feature to its description.

Question 4

A developer has written a Java class that uses external libraries packaged as JAR files. The application runs correctly when launched from an IDE but fails with a ClassNotFoundException when run from the command line using `java -cp`. What is the most likely cause?

Accepted Answer

The JAR files are not listed in the classpath argument.. When running a Java application from the command line with `java -cp`, the classpath must explicitly include all JAR files and directories containing the required classes. If the external library JARs are not listed in the `-cp` argument, the class loader cannot find them, resulting in a `ClassNotFoundException`. IDEs typically manage the classpath automatically, which is why the application works there but fails from the command line.

Answer

The classpath is missing the directory containing the class files.

Answer

The JAR files are not in the module path.

Answer

The Java command should use java -jar instead.

Question 5

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 6

An application built with Java 17 uses a third-party library that internally uses `sun.misc.Unsafe`. The application runs without errors on Java 8 but throws an `IllegalAccessError` on Java 17. What is the most likely reason?

Accepted Answer

Strong encapsulation of JDK internals is enforced by default.. In Java 17, strong encapsulation of JDK internals is enforced by default, meaning that code cannot access internal APIs like `sun.misc.Unsafe` via reflection or direct use unless explicitly opened. The `IllegalAccessError` occurs because the third-party library attempts to use `sun.misc.Unsafe`, which is a JDK internal API that is no longer accessible by default. This change was introduced as part of JEP 403 (Strongly Encapsulate JDK Internals) and finalized in Java 17, whereas Java 8 allowed such access.

Answer

The --illegal-access flag is set to permit.

Answer

The module path does not include the library.

Answer

The library is not in a named module.

Question 7

A Java application packaged as a JAR file with a manifest containing `Main-Class: com.example.Main` is correctly run using `java -jar app.jar`. However, when run with `java -cp app.jar com.example.Main`, it throws a `NoClassDefFoundError` for a class `com.example.helper.Util`. What is the most likely cause?

Accepted Answer

The JAR's manifest Class-Path entry is not being honored when using -cp.. When using `java -jar`, the JVM reads the manifest's `Class-Path` entry to locate dependencies. However, when using `-cp` (or `-classpath`), the manifest's `Class-Path` is ignored; the classpath is determined solely by the `-cp` argument. Since `com.example.helper.Util` is not on the explicit classpath, a `NoClassDefFoundError` occurs. This is a fundamental difference in how the JVM resolves classpaths between the two launch modes.

Answer

The Util class is missing from the JAR.

Answer

The -jar option automatically adds the JAR's dependencies to the classpath.

Answer

The main class name is misspelled.

Question 8

A developer creates a module `com.example.app` that requires `java.sql` and `com.example.util`. The module is compiled and packaged into a JAR. When launching the application with `java --module-path app.jar:lib --module com.example.app`, it fails with `java.lang.module.ResolutionException: Module com.example.util not found`. What is the most likely cause?

Accepted Answer

The module `com.example.util` is not in the module path.. The error `Module com.example.util not found` indicates that the module system cannot locate `com.example.util` on the module path. Since the command specifies `--module-path app.jar:lib`, the JAR for `com.example.util` must be present in the `lib` directory (or another directory on that path). If it is missing or not in the correct location, the module resolution fails. Option B correctly identifies that the module is simply not on the module path.

Answer

The module `com.example.util` is an automatic module and requires specific flags.

Answer

The module `com.example.util` is a named module but not exported.

Answer

The module `com.example.util` is on the classpath and not visible to module system.

Question 9

A company uses a multi-release JAR (MR-JAR) that contains classes for Java 9 and Java 11 in `META-INF/versions/9/` and `META-INF/versions/11/` respectively. The application runs on Java 17. Which version of a class that exists in both versioned directories is loaded?

Accepted Answer

The version from META-INF/versions/11/. Option C is correct because in a multi-release JAR (MR-JAR), the Java runtime selects the versioned directory that matches the major version of the running Java platform, or the highest versioned directory that does not exceed that version. Since the application runs on Java 17, and the highest available versioned directory is for Java 11 (META-INF/versions/11/), the class from that directory is loaded. The root directory is used only when no appropriate versioned directory exists.

Answer

The version from META-INF/versions/9/

Answer

The version from the root of the JAR

Answer

The version from META-INF/versions/17/

Question 10

Which command creates a custom runtime image containing only the modules needed by an application, reducing the size of the JRE?

Accepted Answer

jlink. The `jlink` tool is specifically designed to create a custom runtime image that contains only the modules required by a given application, along with their transitive dependencies. This reduces the JRE size by eliminating unused modules, which is a key feature of Java's module system (Project Jigsaw). Option C is correct because `jlink` is the only command among the choices that performs this modular runtime image assembly.

Answer

jmod

Answer

jar

Answer

jdeps

Question 11

A developer wants to include a module in a custom runtime image using jlink. The module's `module-info.java` does not explicitly export any packages. When running the application from the custom image, a ClassNotFoundException is thrown for a class from that module. What is the most likely cause?

Accepted Answer

The module's packages are not exported, making them invisible to other modules.. Option B is correct because if a module's `module-info.java` does not explicitly export any packages, those packages are not accessible to other modules at runtime. Even if the module is included in the custom runtime image via jlink, the `ClassNotFoundException` occurs because the class is not exported, making it invisible to other modules. The `jlink` tool includes the module's classes in the image, but without an `exports` directive, the packages remain encapsulated.

Answer

The application does not require the module.

Answer

The module uses an automatic module that is not present.

Answer

The module was not included in the jlink command.

Question 12

An application uses `--add-opens java.base/java.lang=ALL-UNNAMED` to allow reflective access to `java.lang` internals from the classpath. After migrating to a module, the flag is changed to `--add-opens java.base/java.lang=com.example.app`. Yet reflective access still fails with `InaccessibleObjectException`. What is the most likely reason?

Accepted Answer

The reflective call is made from a different module than com.example.app.. Option D is correct because `--add-opens` specifies which module's package is opened to which target module. When the flag is changed from `ALL-UNNAMED` to `com.example.app`, only code in the `com.example.app` module is granted reflective access. If the reflective call originates from a different module (e.g., a third-party library or another application module), the `InaccessibleObjectException` will still be thrown because that module is not listed as the target.

Answer

The class performing reflection is in an unnamed module.

Answer

The module does not read the module java.base.

Answer

The module name in --add-opens is misspelled.

Question 13

Which TWO statements are true about the Java module system?

Accepted Answer

The --add-exports flag can be used to export a package from one module to a specific target module.. Option B is correct because the --add-exports command-line flag allows you to export a package from one module to a specific target module at runtime, overriding the module system's encapsulation. This is useful for modules that do not export a package by default but need to be accessed by a specific module during development or testing.

Answer

The --add-exports command-line flag opens a package for deep reflection.

Answer

The jlink tool can generate module-info.java files for automatic modules.

Answer

The exports directive can be used to export a specific class to another module.

Question 14

Which THREE are valid Java commands for launching a modular application?

Accepted Answer

java -p mods -m com.app. Options A, C, and D are correct. Option A: correct syntax for module path and main module. Option B: invalid because --add-modules cannot specify a module with a main class; -m is used. Option C: valid with single module path. Option D: valid with classpath and module path. Option E: invalid because -p is for module path, not classpath.

Answer

java -p classes -m com.app

Answer

java -p mods --add-modules com.app -m com.app

Question 15

Which TWO are characteristics of a multi-release JAR (MR-JAR)?

Accepted Answer

The root of the JAR contains classes for the oldest supported version.. Option A is correct because in a multi-release JAR (MR-JAR), the root of the JAR contains the classes compiled for the oldest supported Java version. This ensures backward compatibility: when the JAR is run on an older JVM that does not understand the META-INF/versions directory, it will use the classes from the root. The JVM automatically selects the appropriate versioned class from the META-INF/versions/<version>/ directory based on the major version of the running Java runtime.

Answer

The version directory must be named with the full version string like "9.0.4".

Answer

It can only contain a single version of each class.

Answer

It is created using the jlink tool.