Welcome to the Ranch. The code you posted is a little bit hard to read. Please use code tags, so that the forum software can properly format your code.
Member variables are initialized to null by default (if you don't initialize them explicitly). In your first example, the member variable commonDao will be null, because you don't initialize it. If you try to call a method on a variable that's null, you'll get a NullPointerException. It must be initialized to refer to some object before you try to call any methods on it.