Abstract class contains methods must be an abstract class, an abstract class but not necessarily contain abstract methods.
If they have a common concept of a lot of things, this common concept itself is not the reality of existence, the collection of these concepts together classified as a class, can be an abstract class.
As for the abstract class has no method, which depends on a lot of things there is no common behavior, but if they have the same nature, but there is no common behavior, which is reasonable.