netbeans.apache.org/src/content/wiki/DevFaqWhatIsAModule.asciidoc

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= DevFaqWhatIsAModule
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:jbake-tags: wiki, devfaq, needsreview
:jbake-status: published
:keywords: Apache NetBeans wiki DevFaqWhatIsAModule
:description: Apache NetBeans wiki DevFaqWhatIsAModule
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=== What is a module?

NetBeans is a _modular_ application.  That means it is composed of pieces, which are discovered at runtime.  Some of those pieces may even be downloaded and installed or uninstalled at runtime.

A module is a library.  It is a Java JAR (Java ARchive) file which contains some classes.  

NetBeans is a Java application.  It has a very small core runtime which knows how to find the modules that make up the application (the launcher passes a list of directories - these are commonly called link:DevFaqWhatIsACluster.asciidoc[clusters] - which contain module JAR files and some XML metadata about them).

All real functionality of the NetBeans IDE or any NetBeans-based application is implemented as modules.

A module JAR contains some additional entries in its META-INF/MANIFEST.MF file, which tell NetBeans about the module - its name, its version, etc.

One distinction about NetBeans modules, as opposed to just working with JAR files on your classpath is that the NetBeans runtime link:DevFaqModuleDependencies.asciidoc[enforces dependency management] between modules - to call code in another module from yours, your module must _declare a dependency_ on the other module.

Another significant distinction is that a module can specify which (if any) packages it makes visible to modules that depend on it - so it is possible to have Java packages in a module's JAR file which are visible only to other classes within that JAR file.  That, in effect, extends Java's class visibility-scoping rules (public, protected, private, package-private) to include _public only within this JAR file_.

=== Apache Migration Information

The content in this page was kindly donated by Oracle Corp. to the
Apache Software Foundation.

This page was exported from link:http://wiki.netbeans.org/DevFaqWhatIsAModule[http://wiki.netbeans.org/DevFaqWhatIsAModule] , 
that was last modified by NetBeans user Tboudreau 
on 2010-02-12T20:09:23Z.


*NOTE:* This document was automatically converted to the AsciiDoc format on 2018-02-07, and needs to be reviewed.