What is a Functional interface in Java 8? What does @Functional annotation do?

What is Functional interface in Java 8

Well, a functional interface is nothing but an interface with just one abstract method e.g. Comparable, Runnable, EventListener, Comparator, etc. You can see these interfaces were present in Java even before JDK 8, but why do we call such interface functional interface?

Explain comparable interface in java

By using Comparable we can sort the objects based on any data member. For example, lets say we have an Author class has data members: Author name, book name and author age, now if we want to sort the objects based on any of the data member then we can use Comparable but what if we want to have multiple sort choices and we can sort objects based on any choice, this can be done using

Abstract class in java can’t be instantiated

Because that would contravene their whole purpose.

Abstract classes, by design, are not complete or functional. They are meant to serve as a base from which complete classes can be built, by aggregating the common members and methods that they all will need into an abstract base class, and then allowing the inheriting classes to fill out the necessary

Abstract Class in Java

Abstract class in Java is similar to interface except that it can contain default method implementation. An abstract class can have an abstract method without body and it can have methods with implementation also.