Some refactoring and program to interface. but, I don't know how to make
added features to make interface.
extends exist interface? Isn't it complicate?
Now that, Some Test class has Strong coupled Generator class.
And Some Generator class's static methods are called by other classed,
such as Checker. This coupling is very bad I think.
But I'm not sure have to move th Util class. Because these method are
very conhensive with that BlockCodes.