The difference is that NG1 was worth using as a good, dependable, and flexible platform. Then all the others happened. "Never attribute to malice that which can be explained by stupidity." - Hanlon's Razor

1)ABSTRACT CLASS -It contains both declaration and definition part. -Multiple inheritance is not achieved by abstract class. -It contain constructor. -It can contain static members. -A class can only use one abstract class. -It can be fully, partially or not implemented. -An abstract class can have non-abstract methods. 2)INTERFACE -It contains only a declaration part. -Multiple inheritance is achieved by interface. -It does not contain constructor. -It does not contain static members. -A class can use multiple interface. -It should be fully implemented. -Interface has only abstract methods.

API API is the acronym for Application Programming Interface. It is a software interface that allows two applications to interact with each other without any user intervention. APIs provides product or service to communicate with other products and services without having to know how they're implemented. Web Service A Web service is a collection of open protocols and standards which are widely used for exchanging data between systems or applications. Software applications are written using various programming languages and running on multiple platforms. It allows you to use web services to exchange data over computer networks.