Java programs are represented in compiled, binary form as class files. Java class files are used not only to execute programs on a Java virtual machine, but also to provide type and name information to a Java compiler. In the latter role, a class file is essentially used to document the API of its class to client code. That client code is compiled into its own class file, including symbolic references used to dynamically link to the API class at runtime.

Java Card technology uses a different strategy for binary representation of programs. Executable binaries and interface binaries are represented in two separate files. These files are respectively called CAP files (for converted applet) and export files.