The compiler should catch errors like this. As you are apparently getting this at runtime, something odd has happened. Probably you have changed the source code but fully recompiled.
Another potential, but obscure, problem is loading the classes through different class loaders. Classes loaded from different class loaders will be in different packages even if the package name is the same (in the same way as classes with the same name loaded by different class loaders will be different classes).
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
