Book Image

Learn Kotlin Programming - Second Edition

By : Stephen Samuel, Stefan Bocutiu
Book Image

Learn Kotlin Programming - Second Edition

By: Stephen Samuel, Stefan Bocutiu

Overview of this book

Kotlin is a general-purpose programming language used for developing cross-platform applications. Complete with a comprehensive introduction and projects covering the full set of Kotlin programming features, this book will take you through the fundamentals of Kotlin and get you up to speed in no time. Learn Kotlin Programming covers the installation, tools, and how to write basic programs in Kotlin. You'll learn how to implement object-oriented programming in Kotlin and easily reuse your program or parts of it. The book explains DSL construction, serialization, null safety aspects, and type parameterization to help you build robust apps. You'll learn how to destructure expressions and write your own. You'll then get to grips with building scalable apps by exploring advanced topics such as testing, concurrency, microservices, coroutines, and Kotlin DSL builders. Furthermore, you'll be introduced to the kotlinx.serialization framework, which is used to persist objects in JSON, Protobuf, and other formats. By the end of this book, you'll be well versed with all the new features in Kotlin and will be able to build robust applications skillfully.
Table of Contents (21 chapters)
Free Chapter
1
Section 1: Fundamental Concepts in Kotlin
5
Section 2: Practical Concepts in Kotlin
15
Section 3: Advanced Concepts in Kotlin

Visibility modifiers

When you define your class, contained methods, properties, or fields can have various visibility levels. In Kotlin, there are four possible values:

  • Public: This can be accessed from anywhere
  • Internal: This can only be accessed from the module code
  • Protected: This can only be accessed from the class defining it and any derived classes
  • Private: This can only be accessed from the scope of the class defining it

If the parent class specifies that a given field is open for being redefined (overwritten), the derived class will be able to modify the visibility level. Here is an example:

    open class Container { 
      protected open val fieldA: String = "Some value" 
    } 
    class DerivedContainer : Container() { 
      public override val fieldA: String = "Something else" 
    } 

Now in the main class, you can create a new DerivedContainer...