Java Platform Module System: Difference between revisions

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== Properties of modules ==

Modules are aused newto waygroup ofpackages groupingand codetightly control what packages belong to the public API. Contrary to [[JAR (file format)|Jar files]], modules explicitly declare which modules they depend on, and what packages they export.<ref>{{cite web

| url=http://openjdk.java.net/projects/jigsaw/spec/sotms/

| title=The State of the Module System

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}}</ref> For example, the majority of the Java standard library is exported by the module <code>java.base</code>.

ModulesAs of Java 25, modules can themselves be imported, automatically importing all exported packages.<ref>{{Cite web|url=https://openjdk.org/jeps/494|title=JEP 494: Module Import Declarations (Second Preview)|website=openjdk.org}}</ref> This is done using <code>import module</code>. For example, <syntaxhighlight lang="Java" inline>import module java.sql;</syntaxhighlight> is equivalent to

<syntaxhighlight lang="Java">

import java.sql.*;

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</syntaxhighlight>

Similarly, <syntaxhighlight lang="Java" inline>import module java.base;</syntaxhighlight>, similarly, imports all 54 packages belonging to <code>java.base</code>.

<syntaxhighlight lang="Java">

import module java.base;

/**

* importing module java.base allows us to avoid manually importing most classes

* the following classes (outside of java.lang) are used:

* java.text.MessageFormat

* java.util.Date

* java.util.List

* java.util.concurrent.ThreadLocalRandom

*/

public class Example {

public static void main(String[] args) {

List<String> colours = List.of("Red", "Orange", "Yellow", "Green", "Blue", "Indigo", "Violet");

IO.println(MessageFormat.format("My favourite colour is {0} and today is {1,date,long}",

colours.get(ThreadLocalRandom.current().nextInt(colours.size())),

new Date()

));

}

}

</syntaxhighlight>

Modules use the following [[List of Java keywords|keywords]]:

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{| class="wikitable plainrowheaders"

! scope="row" | {{code|java.base}}

| Defines the core APIs that form the foundation of the Java SE Platform.
Implicitly required by all modules and does not need to be declared with <code>requires</code> inside a module declaration.

|-

! scope="row" | {{code|java.compiler}}

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|-

! scope="row" | {{code|jdk.xml.dom}}

| Defines the JDK's subset of the [[World Wide Web Consortium]] (W3C) [[Document Object Model]] (DOM) API not covered by Java SE. Exports packages outside of the <code>java</code> namespace (from <code>org.w3c.dom</code>).

|-

! scope="row" | {{code|jdk.zipfs}}

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* [[Classpath]]

* [[Java class loader]]

* [[Precompiled header#Modules]], (C++ modules)]]

== References ==

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[[Category:Java specification requests]]

[[Category:Modularity]]