1Z0-829 Java Platform Overview and Packaging — Timed 20 Questions

Question 1

A Java 17 application is packaged as a JAR with a Main-Class manifest entry. The JAR is run using 'java -jar app.jar'. However, the application throws a NoClassDefFoundError for a class that is inside the JAR. What is the most likely cause?

20 minute time limit — choose an answer to begin.

Accepted Answer

The class is not exported from its module. A NoClassDefFoundError occurs when a class was available at compile time but cannot be loaded at runtime. In a modular Java 17 application, if the class is in a package that is not exported by its module (Option A), classes outside that module cannot access it, leading to the error despite the class being present in the JAR. Additionally, if the JAR file is corrupt (Option C) – for example, due to truncation or CRC mismatch – the JVM cannot read the class bytes properly, also causing NoClassDefFoundError. Therefore, both A and C are common causes. Option B (incorrect Main-Class) would cause the application not to start or a different error. Option D (classpath not set) is irrelevant when using '-jar' as the JVM ignores the classpath.

Answer

The Main-Class manifest entry is incorrect

Answer

The classpath is not set

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 developer has a module named 'com.example.app' that exports a package 'com.example.api'. Another module 'com.example.client' requires 'com.example.app'. Which directive must be in the module-info.java of 'com.example.client'?

Accepted Answer

requires com.example.app;. The 'requires' directive in a module-info.java file declares a dependency on another module. For 'com.example.client' to access the exported packages of 'com.example.app', it must include 'requires com.example.app;'. This is the standard mechanism for module dependency in the Java Platform Module System (JPMS).

Answer

opens com.example.app;

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uses com.example.api;

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exports com.example.api;

Question 4

A Java 17 application is deployed on a server. The application uses modules but one required module is missing from the module path. Which exception will be thrown at startup?

Accepted Answer

ModuleNotFoundException. None of the listed exceptions are correct. When a required module is missing from the module path during startup in Java 17, the module system throws `java.lang.module.FindException`, not `ModuleNotFoundException`. `ExceptionInInitializerError` occurs during static initialization, `NoClassDefFoundError` when a class is missing at runtime, and `ClassNotFoundException` at class loading. `ModuleNotFoundException` is not a standard Java exception.

Answer

ExceptionInInitializerError

Answer

NoClassDefFoundError

Answer

ClassNotFoundException

Question 5

A development team wants to ensure that a Java 17 application runs with a specific set of modules. They want to minimize the footprint by including only necessary modules. Which tool should they use?

Accepted Answer

jlink. B is correct because jlink is the Java tool specifically designed to assemble and optimize a custom runtime image containing only the modules explicitly required by an application. It analyzes module dependencies and produces a minimal JRE, reducing footprint by excluding unused modules, which aligns with the team's goal of minimizing size.

Answer

javac

Answer

jmod

Answer

jar

Question 6

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

Accepted Answer

A module can export a package only to specific modules using 'exports ... to ...'. The 'exports ... to ...' directive in module-info.java restricts the exported package to only the specified target modules, providing fine-grained access control. This is a key feature of the Java module system introduced in Java 9, allowing a module to expose its packages only to trusted modules rather than all other modules.

Answer

All packages in a module are automatically exported.

Answer

The jdeps tool can be used to create a module graph.

Answer

The jlink tool creates a JAR file containing the module.

Question 7

Which THREE are valid ways to package a Java 17 application for distribution? (Choose three.)

Accepted Answer

JMOD file. A is correct because a JMOD file is a native packaging format introduced in Java 9 (JEP 261) specifically for distributing Java modules. It can include compiled classes, native code, configuration files, and even other JMOD files, making it a valid distribution format for Java 17 applications, especially when using the Java Module System.

Answer

ZIP file containing compiled classes

Answer

Shell script that compiles and runs the application

Question 8

A developer runs 'java --list-modules' and sees the output above. Which command can be used to create a custom runtime image containing only the 'java.base' module?

Accepted Answer

jlink --add-modules java.base --output myimage. The `jlink` tool is used to assemble and optimize a set of modules and their dependencies into a custom runtime image. The `--add-modules` option specifies which modules to include, and `--output` specifies the target directory. Option D correctly uses `jlink --add-modules java.base --output myimage` to create a runtime image containing only the `java.base` module.

Answer

jar --create --file myimage --module java.base

Answer

jimage --add-modules java.base --output myimage

Answer

jlink --modules java.base --output myimage

Question 9

A developer receives the above error when running a modular Java application. What is the most likely cause?

Accepted Answer

The module 'com.example.app' is not on the module path.. When a modular Java application throws an error indicating that a module cannot be found, the most common cause is that the module's JAR or directory is not present on the module path. The module path is specified using the `--module-path` option (or `-p`) when launching the application with `java --module`. If `com.example.app` is not on that path, the module system cannot resolve it, leading to a `ModuleNotFoundException` or similar error.

Answer

The module-info.java has a syntax error.

Answer

The JRE version is too old.

Answer

The main class is misspelled.

Question 10

A company runs a Java 17 microservice that reads stock market data from a WebSocket and processes it. The application is packaged as an executable JAR using Maven Shade Plugin. Recently, after a dependency update, the application started throwing 'javax.net.ssl.SSLHandshakeException: PKIX path building failed' when connecting to the WebSocket. The security team insists that no certificates should be imported into the default truststore. The application already includes a custom truststore file 'certs.jks' in the resources folder. The developer had been loading it programmatically but the new dependency uses a different SSL context. The application must trust the WebSocket server without modifying JVM defaults. Which action should be taken?

Accepted Answer

Set the system property 'javax.net.ssl.trustStore' to the path of 'certs.jks' and 'javax.net.ssl.trustStorePassword' to its password.. Setting the system properties 'javax.net.ssl.trustStore' and 'javax.net.ssl.trustStorePassword' overrides the default JVM truststore globally for all SSL contexts within the application. This allows the custom 'certs.jks' file to be used without modifying the JVM's default truststore, satisfying the security team's requirement. The new dependency causing the issue likely uses the default SSL context, which will now pick up the custom truststore via these system properties.

Answer

Add the certificate to the default truststore using keytool and restart the application.

Answer

Use the jlink tool to create a custom runtime image that includes the certificate.

Answer

Create a custom TrustManager that bypasses all certificate validation.

Question 11

Which TWO statements are true about the Java Platform Module System (JPMS) introduced in Java 9?

Accepted Answer

The module declaration is stored in a file named module-info.java.. The module declaration in JPMS is indeed stored in a file named module-info.java, which is compiled into module-info.class and placed at the root of the module. This file defines the module's name, dependencies (requires), and exported packages (exports).

Answer

The module path is searched after the class path when resolving types.

Answer

An automatic module is one that has a module-info.class file at its root.

Answer

A named module can access the unnamed module without any explicit declaration.

Question 12

A developer runs the command above on a JAR file. Which statement accurately describes the module myapp?

Accepted Answer

The module exports com.myapp.internal to the module myapp.tests only.. The command `java --describe-module myapp` outputs the module descriptor, which includes `exports com.myapp.internal to myapp.tests`. This indicates that the module `myapp` exports the package `com.myapp.internal` specifically to the module `myapp.tests` only, not to all modules. The `exports ... to` syntax restricts access to a qualified list of modules.

Answer

The module opens com.myapp.internal for deep reflection to all modules.

Answer

The module provides a service implementation.

Answer

The module requires java.base explicitly; it is not mandated.

Question 13

A team is developing a large enterprise application using Java 17. The application consists of multiple modules: core (provides logging and configuration), services (business logic), and web (REST endpoints). The modules are packaged as separate JAR files and deployed on a server. During runtime, the web module throws a java.lang.ClassNotFoundException for a class that is part of the core module. The core module's module-info.java exports the package containing the missing class. The web module's module-info.java requires core. However, the services module also needs the same class but uses a different version of it, causing conflicts. The team decides to use the class path for the conflicting package and the module path for the rest. They add the conflicting JAR to the class path and keep the other JARs on the module path. After this change, the web module still cannot find the class, but the services module works fine. What is the most likely cause of the issue?

Accepted Answer

The web module is a named module and cannot access classes from a split package that is also in the unnamed module.. When a named module (the web module) is on the module path, it cannot access classes from the unnamed module (the class path) if those classes belong to a package that is also exported by another named module on the module path. This creates a split package, which is forbidden by the Java module system. The core module exports the package, so the web module cannot load the class from the class path JAR, resulting in ClassNotFoundException.

Answer

The services module is using an automatic module, which automatically reads the unnamed module, while the web module is a named module that does not.

Answer

The class path is not scanned for JAR files unless the module path is empty.

Answer

The core module's module-info.java does not export the package to the web module; it only exports it to all modules.

Question 14

Which TWO statements about the Java Platform Module System (JPMS) are true? (Choose two.)

Accepted Answer

JPMS provides reliable configuration through explicit module dependencies.. JPMS enforces reliable configuration by requiring modules to explicitly declare their dependencies using the 'requires' directive in the module descriptor. This eliminates the classpath's silent dependency resolution, where missing or conflicting JARs often cause runtime errors like ClassNotFoundException.

Answer

All classes on the classpath are automatically placed in the boot layer.

Answer

A module declaration is placed in a file named module-info.class.

Answer

JPMS allows the use of the classpath to add modules to the module graph.

Question 15

Given the output of `java --list-modules` from a Java 17 installation, which module is NOT included by default when using the `--release 17` flag with `javac`?

Accepted Answer

jdk.incubator.foreign. The `--release 17` flag restricts `javac` to the standard Java SE 17 API, which does not include incubator modules like `jdk.incubator.foreign`. Incubator modules are preview features that are not part of the Java SE specification and must be explicitly added with `--add-modules`.

Answer

jdk.jfr

Answer

java.net.http

Answer

java.sql

Question 16

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 17

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

Accepted Answer

1. Create a Path object using Paths.get("file.txt"). 2. Call Files.lines(path) to obtain a Stream<String>. 3. Process the stream using stream operations like forEach, filter, etc. 4. Close the stream by calling close() or using try-with-resources.. Files.lines() returns a Stream that must be closed to release file handles. The stream is lazily populated.

Answer

1. Call Files.lines("file.txt") directly with a string. 2. Create a Path object. 3. Process the stream. 4. Close the stream.

Answer

1. Create a Path object. 2. Process the stream (e.g., apply operations). 3. Call Files.lines(path) to get the stream. 4. Close the stream.

Answer

1. Create a Path object. 2. Call Files.lines(path) to get the stream. 3. Close the stream. 4. Process the stream.

Question 18

Match each Java 17 feature to its description.

Accepted Answer

Sealed Classes: A feature that allows a class or interface to restrict which other classes or interfaces may extend or implement it.. These are key features introduced or enhanced in recent Java versions including 17.

Answer

Enhanced NullPointerExceptions: A feature that allows a class to restrict which subclasses can implement it.

Answer

Switch Expressions: A preview feature that allows testing an expression against a pattern using switch.

Question 19

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 20

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