The virtual machine searches for and loads classes in this order:
- Bootstrap classes
- Classes that comprise the Java platform, including the classes in rt.jar and several other important jar files.
- Extension classes
- Classes that use the Java Extension mechanism. These are bundled as jar files located in the extensions directory.
- User classes
- Classes defined by developers and third parties that do not take advantage of the extension mechanism. You identify the location of these classes using the -classpath option on the command line (the preferred method) or by using the CLASSPATH environment variable.