The Java compiler needs to know about all classes, but the JVM does not

I thought this was interesting:

As long as you make sure that a Java class is available before calling its methods or constructor(s), it only needs to be known to the Java compiler, i. e. only at compile time -- and not necessarily at runtime as well. Also, import statements using the name of the class and even declarations using the (imported or fully qualified) class name are always fine -- even if the class is not actually available at runtime.

I wrote some short example code to illustrate this. In main/, there is the main class ImportTest. It is not part of any (explicit) package. That class imports test.Importee and declares a private static member variable of that type. It only instantiates an instance of test.Importee and calls one of its methods if the first command line parameter is true.

• To compile, execute javac */*.java from the top-level directory.
• Now change into main/ and do java ImportTest. This should work and print I can run! Whee!. Note that test.Importee is not present in the classpath.
• Now, from the same directory, do java ImportTest true. This will fail since test.Importee is not present in the classpath...
• That is fixed by java -cp ..:. ImportTest true: Now the JVM can access test.Importee and the program will run, successfully executing the calls to test.Importee. Neat!