If there are no public or protected class found by javadoc, it reports this as an error but returns 0.

Foo.java:
class Foo { }

javadoc Foo.java
Loading source file Foo.java...
Constructing Javadoc information...
javadoc: error - No public or protected classes found to document.

return value is 0, does not match the fact that an error was reported.
Maybe this should be a warning, or it should return non-zero.