Class delegation

Delegation is a design pattern that combines object composition and inheritance. Basically, it is a mechanism where one object delegates actions to another. To see it in action, let's take a look how we would achieve delegation in Java:

public interface Drivable {
void drive();
}

public class Car implements Drivable {

@Override
public void drive() {
System.out.println("Driving a car");
}
}

public class Vehicle implements Drivable {
private Car car;

public Vehicle(Car car) {
this.car = car;
}

@Override
public void drive() {
car.drive();
}
}

public void driveVehicle() {
Car car = new Car();
Vehicle vehicle = new Vehicle(car);
vehicle.drive(); // with delegation, car.drive() get's called
}

In this example, we have the Drivable interface and two classes that implement it. The Vehicle class doesn't have its own drive functionality; rather, it delegates the drive function to the Car object.

If we were to write the same example in Kotlin, it would look like this:

interface Drivable...