The Java Application Programming Interface (API) is a set of classes defined by Sun Microsystems. It provides a range of base functionality that can be used and extended by Java developers. It is the core of “what you can do” with Java.
The Java API offers considerable functionality in its own right. A large portion of the Java API is built in to any database that is enabled to use Java code—which includes the majority of nonvisual classes from the Java API already familiar to developers using the Sun Microsystems JDK.