Note: Optional packages are the new name for what used to be known as
standard extensions. The "extension mechanism"
is that functionality of the Java 2 SDK and Java 2 Runtime Environment
that supports the use of optional packages.
Optional packages are packages of Java classes (and any associated native
code) that application developers can use to extend the functionality
of the core platform. The extension mechanism allows the Java virtual
machine (VM) to use the classes of the optional extension in much the same way as the
VM uses classes in the Java 2 Platform. The extension mechanism also provides a way for
needed optional packages to be retrieved from specified URLs when they are not
already installed in the Java 2 SDK or Runtime Environment.
Enhancements
Enhancements to the
extension mechanism in version 1.3 of the Java 2 SDK include an
extended set of manifest attributes that can be used for
checking vendor and versioning information of installed optional packages.
If an applet requires an optional package that isn't installed, or that
is installed but has the wrong version number or is not from
the appropriate vendor, the Java Plug-in can download the
needed extension from a specified URL. For more information,
see Optional-Package Versioning.
Overview
Overview -
What optional packages are and how to use them.