Answer: Abstract class must contain atleast one abstract method. Abstract method does not provide actual implementation of the methods. It just provides method signature. Actual implementation is left to the class which extends the Abstract class. Abstract class may contain concrete methods.
Interface is one step further to the idea of Abstract class. In an interface, all method are kept abstract. It does not provide any method with actual implementation.
Any class can extend only one Abstract class. Any class can implement more than one interface.