1Z0-819 Modules System 5 — Questions and Answers
Question 1: What is the module name for the foundational Java SE module that all other modules implicitly depend on?
- java.core
- java.lang
- java.se
- java.base (Correct answer)
Correct answer: java.base
java.base is the foundational platform module containing java.lang, java.util, java.io, etc., and every module implicitly requires it.
Question 2: What command lists all observable modules in the current JDK installation?
- java --describe-module java.se
- jmod list
- java --list-modules (Correct answer)
- jlink --list-modules
Correct answer: java --list-modules
'java --list-modules' outputs all platform and observable modules available to the current JDK.
Question 3: A module-info.java declares 'opens com.example.data to com.google.gson;'. What capability does this grant?
- Only public method calls on types in com.example.data by com.google.gson
- com.google.gson can load classes from com.example.data with a custom ClassLoader
- com.google.gson can re-export com.example.data to other modules
- com.google.gson can reflectively access all members including private ones in com.example.data (Correct answer)
Correct answer: com.google.gson can reflectively access all members including private ones in com.example.data
A qualified 'opens' directive allows the target module to use reflection on all members, including private ones, in the opened package.
Question 4: What is the key difference between placing a JAR on --class-path versus --module-path?
- On --class-path the JAR exports all packages; on --module-path it exports none by default
- On --module-path the JAR is compiled; on --class-path it runs interpreted
- There is no difference; both paths are merged by the JVM at startup
- On --class-path it joins the unnamed module; on --module-path it becomes an automatic or named module (Correct answer)
Correct answer: On --class-path it joins the unnamed module; on --module-path it becomes an automatic or named module
Classpath JARs are aggregated into the unnamed module, while module-path JARs become named or automatic modules with encapsulation enforced.
Question 5: Which @Deprecated attribute, added in Java 9 alongside the module system, marks an API slated for removal?
- forRemoval=true (Correct answer)
- since="9", removal=true
- obsolete=true
- status=REMOVAL
Correct answer: forRemoval=true
The 'forRemoval=true' attribute on @Deprecated was added in Java 9 to signal that an API is scheduled for removal in a future release.
Question 6: What does the '--patch-module' option do when launching the JVM?
- Merges additional classes or resources into an existing named module at runtime (Correct answer)
- Replaces the module-info.class of a module with a custom descriptor
- Applies security patches to platform modules without recompiling
- Forces a module to re-read its module-info.class from disk
Correct answer: Merges additional classes or resources into an existing named module at runtime
'--patch-module module=path' injects additional classes into a named module, useful for testing and patching platform classes.
Question 7: Which module aggregates all standard Java SE API modules so you can depend on the full Java SE platform at once?
- java.base
- java.platform
- java.se (Correct answer)
- java.all
Correct answer: java.se
'java.se' is an aggregator module that requires all standard Java SE modules (java.desktop, java.sql, java.xml, etc.) transitively.
1Z0-819 Modules System 5
What is the module name for the foundational Java SE module that all other modules implicitly depend on?