Application Structure | Modularity | Project Jigsaw | Java 9 | Part 22

We will discuss about application structure, first will discuss about
Module declaration
Which always starts with the keyword module, followed by a unique module name and module body enclosed in braces like

module modulename{
}

The module declaration’s body can be empty or may contain various module directives, likerequires, exports, uses and opens.

The keywords exports, module, open, opens, provides, requires, uses, with, and
transitive are restricted keywords as we need to use only in module declarations and may be used as identifiers anywhere else in your code.

As we know in Java 9 Module System, We can use “module”, “requires”, and “exports” keywords to describe a Module Meta Data in a Module Descriptor.
However, all these 3 are not keywords. They are just “Contextual Keywords” only. That means they are keywords only with a Module Descriptor (“module-info.java”) file.
If we used them as Identifiers in the existing code base, Java Compiler or Run-time does NOT throw any error or Exceptions at compile-time and run-time.

In this section, we create a simple Hello world app to demonstrate module fundamentals. We
■■ create a class that resides in a module
■■ provide a module declaration
■■ compile the module declaration and Hello world class into a module
■■ run the class containing main in that module
■■ after discussing them we will go with, packaging the HelloWorld app in a modular JAR file
■■ running the app from that JAR file

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Please watch: "What is JShell ? | Practical explanation of JShell | Java 9 feature JShell | JShell | REPL"
https://www.youtube.com/watch?v=T-e1EnKgWq0
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