The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
Any set of packages or classes can easily be made to play the role of an extension. The first step in turning a set of classes into an extension is to bundle them in a JAR file. Once that's done, you can turn the software into an extension in two ways:
This lesson shows you how the extension mechanism works by using a simple "toy" extension as an example.
In this section, you'll create a simple installed extension and see how extension software is treated as part of the platform by the runtime environment.
This section will show you how modify a JAR file's manifest so that the JAR-bundled software can make use of download extensions.
This section is a short detour that summarizes the Java platform's delegation model for loading classes, and shows how it relates to loading classes in extensions.
This section discusses the mechanism used to extend an application, via plug-ins or modules, without modifying its original code base.
The next lesson, Making Extensions Secure uses the same extension to show how the Java platform controls the security permissions that are granted to extensions.