Chapter 12: Modules Flashcards
What is the main purpose of the Java Platform Module System (JPMS)?
JPMS groups related packages into modules, allowing controlled access and improved code organization.
How does JPMS compare to JAR files?
Like a JAR file, but with explicit control over which packages are accessible outside the module.
What are the three key components of JPMS?
Module JAR format, JDK partitioning into modules, and additional Java tool command-line options.
What is a module in Java?
A group of one or more packages plus a module-info.java file that declares module properties.
Why were Java modules introduced? 5 items
To improve access control, dependency management, security, performance, and to support custom Java builds.
How do modules provide better access control?
They allow packages to be accessible only within the module, preventing unintended access.
How do modules improve dependency management?
They declare dependencies, enabling Java to detect missing JARs at startup instead of runtime.
What is a key advantage of using custom Java builds?
They include only necessary JDK components, reducing runtime size and improving efficiency.
How do modules enhance security?
By omitting unused JDK parts, reducing exposure to vulnerabilities.
How do modules improve performance?
Smaller runtime size leads to faster startup and lower memory usage.
What is unique package enforcement in Java modules?
Ensures each package comes from only one module, preventing conflicts and confusion.
How do Java modules enforce strong encapsulation?
Packages are not accessible by default; only explicitly exported packages can be used by other modules.
What keyword is used to expose a package in Java modules?
The exports keyword, e.g., exports com.example.api;.
How can a module restrict access to its exported packages?
By using exports … to, e.g., exports com.example.api to com.example.moduleB; to limit access to a specific module.
How can a module allow reflective access to a package?
Using the opens keyword, e.g., opens com.example.internal to some.framework.module;.
What does the requires keyword do in a Java module?
It specifies dependencies on other modules, ensuring only required modules are accessible.
What does the –module-path option do in Java’s module system?
The –module-path option specifies the locations of required modules. It allows the Java runtime to locate and load modules that are needed for execution. Multiple module paths can be separated using ; on Windows or : on macOS/Linux.
How do you execute a specific class from a named module using the –module option?
The –module option is used to specify a module and the class within it that should be executed.
What is a named module in Java?
A named module is a module that has an explicit name defined in a module-info.java file. It is part of Java’s module system and follows strict encapsulation rules. Named modules explicitly declare their dependencies and exported packages.
How is a named module different from an unnamed module?
A named module has a module-info.java file and follows strict module rules, whereas an unnamed module does not have a module descriptor and can access all other modules. Named modules provide better encapsulation and dependency management.
