Interface

• Interface is basically a replacement for for extending classes since we can implement as many interfaces as we want in a Class.
• Interface basically has two main components
  • Constants (By default)
  • Methods (They do not have data type)
• When we implement the Interface to a class then we need to define all the methods of the Interface.

Abstract

• It is any class having one or more abstract methods.
• Abstract is similar to Interface. The difference: Not all methods need to be over-ridden; common methods can be defined within the Abstract class itself.
• Objects of Abstract classes cannot be made. It can only be inherited.
• If one or more method is declared abstract, its class must also be abstract.
• When we extend an Abstract Class to a Class, we need to define all the methods defined in the Abstract Class else the derived class again should be Abstract.
• It can have final methods i.e. methods that cannot be over-ridden.