1Z0-829 Practice Test 29 — 15 Questions

Question 1

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 2

In a modular Java application, where does the module declaration file typically reside?

Accepted Answer

In a file named module-info.java at the root of the module's source tree. Option C is correct because the module declaration for a modular Java application must be placed in a file named `module-info.java` at the root of the module's source tree. This file is then compiled into `module-info.class` and placed in the output directory, but the source declaration resides in the source tree root as per the Java Platform Module System (JPMS) specification.

Answer

In a file named module-info.class in the output directory

Answer

In the META-INF directory

Answer

In the root of the source directory

Question 3

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 4

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.. Option D is correct because 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 5

Which TWO statements about module descriptors are true?

Accepted Answer

A module descriptor can use the opens keyword to enable deep reflection on specific packages.. Option B is correct because the `opens` keyword in a module descriptor (module-info.java) allows deep reflection (access to private members) on specific packages at runtime, which is necessary for frameworks like Hibernate or JPA that rely on reflection. Option E is correct because the `transitive` keyword is used only within `requires` directives to indicate that any module that requires the current module also implicitly requires the specified module.

Answer

A module descriptor can use the provides keyword to declare that it uses a service.

Answer

A module descriptor must require the java.base module explicitly.

Answer

A module descriptor can specify which packages are exported with the export keyword.

Question 6

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 7

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 8

A developer places a non-modular JAR file on the module path. What type of module does this JAR become?

Accepted Answer

Automatic module. When a non-modular JAR is placed on the module path, the Java module system automatically derives a module from it, known as an automatic module. This is because the JAR lacks a module-info.class, so the system infers a module name from the JAR filename (e.g., using the Main-Class attribute or the JAR's name) and exports all packages, giving it access to all other modules. Option C is correct because the JAR becomes an automatic module, not a named or unnamed module.

Answer

Open module

Answer

Named module

Answer

Unnamed module

Question 9

Given two named modules where module com.example.app requires module com.example.lib, which packages of com.example.lib are readable by com.example.app?

Accepted Answer

Only the packages exported by com.example.lib. Option D is correct because in the Java module system, a module can only access packages from another module that are explicitly exported using the `exports` directive in the module's `module-info.java` file. Since `com.example.app` requires `com.example.lib`, only the packages exported by `com.example.lib` are readable; unexported packages remain encapsulated and inaccessible.

Answer

All packages except those explicitly concealed

Answer

All packages of com.example.lib

Answer

Only the packages opened by com.example.lib

Question 10

Which THREE statements about the jpackage tool are true?

Accepted Answer

jpackage can create native installers for Windows, macOS, and Linux.. Option C is correct because 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 11

A developer creates a Java application that uses the new 'jpackage' tool to create an installer for Windows. The application is modular and has a main class declared in module-info. Which option is required to specify the main class when using jpackage?

Accepted Answer

--module. For a modular application with a main class declared in module-info, jpackage requires the `--module` option to specify the module name and, optionally, the main class (e.g., `--module com.example/com.example.Main`). This is because jpackage uses the module system to resolve the entry point, not a classpath or JAR-based approach.

Answer

-classpath

Answer

--module-path

Answer

--main-jar

Question 12

A developer is migrating a classpath-based application to modules. They have two JARs on the classpath that both contain a package with the same name, com.example.util. When they move both JARs to the module path, they encounter a module resolution error. What is the most likely cause?

Accepted Answer

Named modules cannot have split packages. In the Java module system, a package can be defined in at most one module on the module path. When both JARs contain com.example.util, moving them to the module path creates a split package, which is illegal for named modules. The module system enforces this to ensure reliable configuration and encapsulation, resulting in a module resolution error.

Answer

The --add-exports option is missing

Answer

The JARs need to be merged into one module

Answer

Automatic modules cannot have split packages

Question 13

A company uses jlink to create a custom runtime image. They want to reduce the image size by removing debug information. Which jlink option or plugin should they use?

Accepted Answer

--strip-debug. The `--strip-debug` option in jlink removes debug information from the custom runtime image, including line numbers, local variable tables, and source file references, which significantly reduces the image size. This is the correct option for stripping debug information, as it directly targets the removal of debugging metadata from the generated image.

Answer

--compress=2

Answer

--no-header-files

Answer

--bind-services

Question 14

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 $JAVA_HOME/jmods:app --add-modules com.myapp --output myimage. Option A is correct because `jlink` with `--add-modules com.myapp` and the module path pointing to both `$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 15

Which TWO statements about Java module types are true?

Accepted Answer

An automatic module exports all its packages.. Option A is correct because 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.