Book Image

Kotlin Programming Cookbook

By : Aanand Shekhar Roy, Rashi Karanpuria
Book Image

Kotlin Programming Cookbook

By: Aanand Shekhar Roy, Rashi Karanpuria

Overview of this book

The Android team has announced first-class support for Kotlin 1.1. This acts as an added boost to the language and more and more developers are now looking at Kotlin for their application development. This recipe-based book will be your guide to learning the Kotlin programming language. The recipes in this book build from simple language concepts to more complex applications of the language. After the fundamentals of the language, you will learn how to apply the object-oriented programming features of Kotlin 1.1. Programming with Lambdas will show you how to use the functional power of Kotlin. This book has recipes that will get you started with Android programming with Kotlin 1.1, providing quick solutions to common problems encountered during Android app development. You will also be taken through recipes that will teach you microservice and concurrent programming with Kotlin. Going forward, you will learn to test and secure your applications with Kotlin. Finally, this book supplies recipes that will help you migrate your Java code to Kotlin and will help ensure that it's interoperable with Java.
Table of Contents (21 chapters)
Title Page
Copyright and Credits
Packt Upsell
Contributors
Preface
Index

How to sort a list of objects and keep null objects at the end


We have already seen how to sort a list based on a specified parameter using a comparator. However, so far, we have worked with lists having non-null values. In this recipe, we will see how to sort a list of objects, which have the null property (on which we are sorting). So let's get started.

Getting ready

I'll be using IntelliJ IDEA for writing and running Kotlin code; you are free to use any IDE that can do the same task.

How to do it…

Now, let's follow these steps to sort a list, while keeping null objects at the end:

  1. Let's create a Person class having an age property that can be null:
class Person(var age:Int?)
  1. Now, let's create a list of Person objects:
val listOfPersons=listOf(Person(10), Person(20), Person(2), Person(null))
  1. Finally, we want to sort them in ascending order, while keeping the null items at the end:
val sortedList=listOfPersons.sortedWith(compareBy(nullsLast<Int>(),{it.age}))
sortedList.forEach {
    print(...