Book Image

Android Development with Kotlin

By : Igor Wojda, Marcin Moskala
Book Image

Android Development with Kotlin

By: Igor Wojda, Marcin Moskala

Overview of this book

Nowadays, improved application development does not just mean building better performing applications. It has become crucial to find improved ways of writing code. Kotlin is a language that helps developers build amazing Android applications easily and effectively. This book discusses Kotlin features in context of Android development. It demonstrates how common examples that are typical for Android development, can be simplified using Kotlin. It also shows all the benefits, improvements and new possibilities provided by this language. The book is divided in three modules that show the power of Kotlin and teach you how to use it properly. Each module present features in different levels of advancement. The first module covers Kotlin basics. This module will lay a firm foundation for the rest of the chapters so you are able to read and understand most of the Kotlin code. The next module dives deeper into the building blocks of Kotlin, such as functions, classes, and function types. You will learn how Kotlin brings many improvements to the table by improving common Java concepts and decreasing code verbosity. The last module presents features that are not present in Java. You will learn how certain tasks can be achieved in simpler ways thanks to Kotlin. Through the book, you will learn how to use Kotlin for Android development. You will get to know and understand most important Kotlin features, and how they can be used. You will be ready to start your own adventure with Android development with Kotlin.
Table of Contents (16 chapters)
Title Page
About the Authors
About the Reviewers
Customer Feedback
Making Your Marvel Gallery Application

Sealed classes

A sealed class is a class with a limited number of subclasses (sealed subtyping hierarchy). Prior to Kotlin 1.1, these subclasses had to be defined inside a sealed class body. Kotlin 1.1 weakened this restriction and allowed us to define sealed class subclasses in the same file as a sealed class declaration. All the classes are declared close to each other, so we can easily see all possible subclasses by simply looking at one file:


    sealed class Vehicle()
    class Car : Vehicle()
    class Truck : Vehicle()
    class Bus : Vehicle()

To mark a class as sealed, simply add a sealed modifier to the class declaration header. The preceding declaration means that the Vehicle class can be only extended by three classes, Car, Truck, and Bus because they are declared inside the same file. We could add a fourth class in our vehicle.kt file, but it would not be possible to define such a class in another file.

The sealed subtyping restriction only applies to direct...