1) For Interfaces, you cannot have any kind of concrete method.
But in the abstract class, apart from having only abstract methods you can also have some methods for which implementation is provided. i.e., you will have atleast one method declared as abstract.
2)And also Interfaces can extend 1 or more interface, whereas the abstract classes cannto extend more than 1 class.
In other words.. abstract classes are some what flexible when compared to interfaces.