C4 - Lesson 4: Java Modules

Question 1

export

Answer 1

exports: Identify a package that should be available to users of this module. Takes a package name as a parameter. Does not include subpackages.

Question 2

requires

Answer 2

• requires: Make the packages in the specified module available in this module. You cannot require a package that also requires you
• Is like the import

Question 3

module descriptor

Answer 3

• it is the modules-info.java
• module name
  indicates which packages the module makes available, as well as which modules this module relies on
• has the “module” keyword

Question 4

modules

Answer 4

• Is a jar

- They also contain one additional class called a module descriptor modules-info.java

Question 5

MODULEPATH

Answer 5

• you place your modules at a different location, called the MODULEPATH.
• This is the path where the compiler looks for all your modules.

Question 6

to

Answer 6

The to keyword can be used to modify exports to limit which modules can access the specified package.

Question 7

transitive

Answer 7

The transitive keyword modifies the requires keyword and specifies that the required module will also be made available to any other module that includes this module.

Question 8

reflection access.

Answer 8

,

Question 9

CLASSPATH

Answer 9

This is the path where the compiler looks for all your class files.
- Before java 9 building a Java project involved placing all project classes and jars on the CLASSPATH

Question 10

What happens in java 9+ if something does not use modules?

Answer 10

• All Java applications compiled in Java 9+ use the module system
• Even if they contain no modules and do not use a module descriptor, everything placed on the CLASSPATH are placed into what is called the Unnamed Module.

Question 11

Named, Unnamed and automatic modules: Access comparasion

Answer 11

• Named: Named and automatic
• Unnamed: Unnamed and automatic
• automatic: Named and Unnamed

Question 12

Classpath and modulepath in maven

Answer 12

Modulepath

• Modular jars
• Nonmodular dependencies. This become automatics module with same name
• Transitive dependencies that are modules

Classpath
- Transitive dependencies that are not modules

Question 13

open

Answer 13

opens: Makes the specified package available for both public and private class reflection access. Can optionally use the to keyword to limit which modules have this access.