Obviously that doesn't compile, but I hate to make a file FooType.java with just the 5 lines above in it. Obviously that doesn't compile, but I hate to make a file FooType.java with just the 5 ...

In other words, a Java class that supports the SOLID open-closed principle will find use in originally un-envisioned scenarios, and be flexible enough to work with newly created classes, interfaces ...

Enabling frameworks to define classes as non-discoverable implementation details of the framework, so they cannot be linked against by other classes, or discovered via reflection.