1Z0-819 Modules System 3 — Questions and Answers
Question 1: Which JDK tool creates a custom runtime image from a set of modules?
- jmod
- jdeps
- jlink (Correct answer)
- jimage
Correct answer: jlink
'jlink' assembles and optimizes a custom runtime image containing only the specified modules and their transitive dependencies.
Question 2: What does the 'jdeps' tool primarily do in the context of the module system?
- Deploys modular JARs to a runtime image
- Analyzes class files to determine module and package dependencies (Correct answer)
- Lists all modules available in the current JDK
- Creates module-info.java files automatically from JAR metadata
Correct answer: Analyzes class files to determine module and package dependencies
'jdeps' analyzes class-file bytecode and reports module-level and package-level dependencies.
Question 3: What is the unnamed module in Java's module system?
- A module declared without a name in module-info.java
- The bootstrap module containing java.lang classes
- A special module that contains all classes loaded from the classpath (Correct answer)
- An automatic module with no Automatic-Module-Name manifest entry
Correct answer: A special module that contains all classes loaded from the classpath
The unnamed module is a catch-all module that contains all types loaded from the classpath, enabling backward compatibility.
Question 4: Which JVM option allows deep reflection from one named module into a package of another module at runtime without modifying source?
- --add-exports
- --add-reads
- --add-modules
- --add-opens (Correct answer)
Correct answer: --add-opens
'--add-opens module/package=targetModule' grants reflective access similar to an 'opens' directive without modifying module-info.
Question 5: A module-info.java contains 'exports com.example.util to com.app.core;'. This means:
- com.example.util is exported to all modules with com.app.core getting priority
- com.app.core can access all types (including private) in com.example.util
- com.app.core must explicitly import com.example.util to use it
- Only com.app.core can access the public types in com.example.util (Correct answer)
Correct answer: Only com.app.core can access the public types in com.example.util
A qualified export restricts access to the exported package's public types to only the specified module(s).
Question 6: What is the primary purpose of JMOD files created by the 'jmod' tool?
- To serve as runtime JARs on the module path
- To store module source code for documentation
- To package modules including native code for use with jlink (Correct answer)
- To provide binary module descriptors for faster JVM startup
Correct answer: To package modules including native code for use with jlink
JMOD is a packaging format used mainly for JDK modules; it supports native libraries and config files that regular JARs can't include, used by jlink.
Question 7: What happens if two named modules on the module path export the same package?
- The module listed first on the module path takes precedence
- A split package error occurs at startup or compile time (Correct answer)
- The JVM merges the packages and all types are accessible
- Both modules load silently and types are disambiguated by module name
Correct answer: A split package error occurs at startup or compile time
Split packages (the same package in more than one named module) are forbidden and result in an error.
1Z0-819 Modules System 3
Which JDK tool creates a custom runtime image from a set of modules?