The main difference between abstract class and interface is,

1. Abstract class has the constructor, but interface doesn't have.

2. Main reason is abstract class contain the instance variable, that why it has
the constructor, where as interface has only constants (final variables and
ABSTRACT METHODS).

3. A class which can implement the interface, is not implement all methods which
are declared in interface , such class is declared as abstract class. that mean
abstract class is a subtype of an interface.

This is my conclusion. If you have an queries let me know.