Write a Class Inside an Interface in Java

Defining a class within an interface is allowed in Java. If the methods of an interface accept a class as an argument and the class is not used elsewhere, in such cases we can define a class inside an interface.

Example

In the following example we have an interface with name CarRentalServices and this interface has two methods that accepts an object of the class Car as an argument. Within this interface we have the class Car.

 Live Demo

interface CarRentalServices {
   void lendCar(Car c);
   void collectCar(Car c);
   public class Car{
      int carId;
      String carModel;
      int issueDate;
      int returnDate;
   }
}
public class InterfaceSample implements CarRentalServices {
   public void lendCar(Car c) {
      System.out.println("Car Issued");
   }
   public void collectCar(Car c) {
      System.out.println("Car Retrieved");
   }
   public static void main(String args[]){
      InterfaceSample obj = new InterfaceSample();
      obj.lendCar(new CarRentalServices.Car());
      obj.collectCar(new CarRentalServices.Car());
   }
}

Output

Car Issued
Car Retrieved