The compiler first searches the Java platform packages (in rt.jar and other JAR files), which contain Java’s standard class library types (such as java.lang ‘s System class).

Strictly speaking, it isn't possible to list the classes in a package. This is because a package is really nothing more than a namespace (eg com.epicapplications.foo.bar), and any jar-file in the ...

The Java Tutorials ‘ Deployment Trail features the Packaging Programs in JAR Files lesson that includes the relevant section Setting Package Version Information.