Hands-On Object-Oriented Programming with Kotlin

Why do we need sealed classes?

Sealed classes are designed for situations in which a limited set of functionalities are required and no other class is allowed to be part of this set. For example, let's say we are writing an application for an order-delivery service in which a limited number of steps are involved:

1. The order is received at depot
2. The order is dispatched to the customer
3. The order is delivered to the customer

Let's create an Order class with the item property:

class Order(val item : String)

Create a sealed class, OrderDelivery, with one property, Order. We then need to create three child classes, each of which represents one of the steps:

sealed class OrderDelivery(val order : Order) class ReceivedAtDepot(val depotName : String, ...