What's the difference between an interface and an abstract class? Also discuss the similarities. (Very Important)

Abstract class is a class which contain one or more abstract methods, which has to be implemented by sub classes. Interface is a Java Object containing method declaration and doesn't contain implementation. The classes which have implementing the Interfaces must provide the method definition for all the methods
Abstract class is a Class prefix with a abstract keyword followed by Class definition. Interface is a Interface which starts with interface keyword.
Abstract class contains one or more abstract methods. where as Interface contains all abstract methods and final declarations
Abstract classes are useful in a situation that Some general methods should be implemented and specialization behavior should be implemented by child classes. Interfaces are useful in a situation that all properties should be implemented.