In class java.io.File, the mikdir method seems to return false if
the directory in questions already exists. This has two bad
properties:

(1) It is actually difficult to tell, after a call to mkdir, whether the
directory exists, which is usually of greater interest than whether
the transition from nonexistent to existent occurred.

(2) As evidence of this, the value returned by mkdirs is almost
useless. You actually expect one of the parent directories to exist;
so mkdirs almost always returns false. If mkdir were to return true
iff the directory exists after the call to mkdir, then mkdirs would return
true iff the directory (and all its parents) exist after the call to mkdirs.