PrivateAccessor

http://junit-addons.sourceforge.net/junitx/util/PrivateAccessor.html

こいつがあれば

Class clazz = Hoge.getClass();
Fiels field = c.getDeclaredFiled("foo");
field.setAccessible(true);
(String)field.get(clazz);

(String)PrivateAccessor.getField(hoge, "foo");

に変身