Nested Interface Implementation

Animal.java

class Animal{
    // Creating the interface inside class; nested interface.
    interface Activity{
        public default void move(){
            System.out.println("Animal is moving.");
        }
    }
}

Dog.java

// To get access to Nested Interface : we write OuterClassName.NestedClasName
class Dog implements Animal.Activity{
    public void move(){
        System.out.println("Dog is moving.");
    }
}

NestedInterfaceDemo.java

class NestedInterfaceDemo{
    public static void main(String[] args){
        Dog dogObject = new Dog();
        dogObject.move();

        // This is how, we refer to subclass object from nested interface referrer variable.
        Animal.Activity nestedReferrerOne = new Dog();
        nestedReferrerOne.move();
    }
}