The Application Programming Interface, or API, provides all the classes that are included as part of the JDK.
You can view the API documentation from the Java web site, or you can download and install it on your system.
Although it's common to store the API documentation in the JDK directory (usually C:\Program Files\Java\jdk1.6.0 for SE 6), you can store it anywhere you like.
How to navigate the API documentation
You can use your web browser to browse through the API documentation on your own system (if you've downloaded and installed it) or at the Java web site.
Related classes in the Java API are organized into packages, which are listed in the upper left frame of the documentation page.
When you select a package, all the classes for that package are listed in the lower left frame.
You can select a class from the lower left frame to display the documentation for that class in the right frame.
You can also select the name of the package at the top of the lower left frame to display information about the package and the classes it contains.