"The Java Platform APIs are a set of essential interfaces that
developers need to build their Java applications and applets. All
Java Platfrom APIs are open and extensible, and are created by
JavaSoft and industry-wide specialists in each target technology
and market area.
By targeting the Java Platform, developers will be assured that
their applications can run anywhere, without any need to port. The
widespread availability of the Java Platfrom and the
industry-standard Java Platform APIs have created the
highest-volume software application platform available today". (Sun
Microsystems)
Additionally this page shows a lot of class libraries from
different sources.