Kotlin Programming The Big Nerd Ranch Guide.pdf

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Title Page

Dedication

Acknowledgments

Table of Contents

Introducing Kotlin

Why Kotlin?

Who Is This Book For?

How to Use This Book

For the More Curious

Challenges

Typographical conventions

Using an eBook

Looking Forward

1. Your First Kotlin Application

Installing IntelliJ IDEA

Your First Kotlin Project

Creating your first Kotlin file

Running your Kotlin file

Compilation and execution of Kotlin/JVM code

The Kotlin REPL

For the More Curious: Why Use IntelliJ?

For the More Curious: Targeting the JVM

Challenge: REPL Arithmetic

2. Variables, Constants, and Types

Types

Declaring a Variable

Kotlin’s Built-In Types

Read-Only Variables

Type Inference

Compile-Time Constants

Inspecting Kotlin Bytecode

For the More Curious: Java Primitive Types in Kotlin

Challenge: hasSteed

Challenge: The Unicorn’s Horn

Challenge: Magic Mirror

3. Conditionals

if/else Statements

Adding more conditions

Nested if/else statements

More elegant conditionals

Logical operators

Conditional expressions

Removing braces from if/else expressions

Ranges

when Expressions

String Templates

Challenge: Trying Out Some Ranges

Challenge: Enhancing the Aura

Challenge: Configurable Status Format

4. Functions

Extracting Code to Functions

Anatomy of a Function

Function header

Visibility modifier

Function name declaration

Function parameters

Function return type

Function body

Function scope

Calling a Function

Refactoring to Functions

Writing Your Own Functions

Default Arguments

Single-Expression Functions

Unit Functions

Named Function Arguments

For the More Curious: The Nothing Type

For the More Curious: File-Level Functions in Java

For the More Curious: Function Overloading

For the More Curious: Function Names in Backticks

Challenge: Single-Expression Functions

Challenge: Fireball Inebriation Level

Challenge: Inebriation Status

5. Anonymous Functions and the Function Type

Anonymous Functions

The function type

Implicit returns

Function arguments

The it keyword

Accepting multiple arguments

Type Inference Support

Defining a Function That Accepts a Function

Shorthand syntax

Function Inlining

Function References

Function Type as Return Type

For the More Curious: Kotlin’s Lambdas Are Closures

For the More Curious: Lambdas vs Anonymous Inner Classes

6. Null Safety and Exceptions

Nullability

Kotlin’s Explicit Null Type

Compile Time vs Runtime

Null Safety

Option one: the safe call operator

Using safe calls with let

Option two: the double-bang operator

Option three: checking whether a value is null with if

The null coalescing operator

Exceptions

Throwing an exception

Custom exceptions

Handling exceptions

Preconditions

Null: What Is It Good For?

For the More Curious: Checked vs Unchecked Exceptions

For the More Curious: How Is Nullability Enforced?

7. Strings

Extracting Substrings

substring

split

String Manipulation

Strings are immutable

String Comparison

For the More Curious: Unicode

For the More Curious: Traversing a String’s Characters

Challenge: Improving DragonSpeak

8. Numbers

Numeric Types

Integers

Decimal Numbers

Converting a String to a Numeric Type

Converting an Int to a Double

Formatting a Double

Converting a Double to an Int

For the More Curious: Bit Manipulation

Challenge: Remaining Pints

Challenge: Handling a Negative Balance

Challenge: Dragoncoin

9. Standard Functions

apply

let

run

with

also

takeIf

takeUnless

Using Standard Library Functions

10. Lists and Sets

Lists

Accessing a list’s elements

Index boundaries and safe index access

Checking the contents of a list

Changing a list’s contents

Iteration

Reading a File into a List

Destructuring

Sets

Creating a set

Adding elements to a set

while Loops

The break Expression

Collection Conversion

For the More Curious: Array Types

For the More Curious: Read-Only vs Immutable

Challenge: Formatted Tavern Menu

Challenge: Advanced Formatted Tavern Menu

11. Maps

Creating a Map

Accessing Map Values

Adding Entries to a Map

Modifying Map Values

Challenge: Tavern Bouncer

12. Defining Classes

Defining a Class

Constructing Instances

Class Functions

Visibility and Encapsulation

Class Properties

Property getters and setters

Property visibility

Computed properties

Refactoring NyetHack

Using Packages

For the More Curious: A Closer Look at var and val Properties

For the More Curious: Guarding Against Race Conditions

For the More Curious: Package Private

13. Initialization

Constructors

Primary constructors

Defining properties in a primary constructor

Secondary constructors

Default arguments

Named arguments

Initializer Blocks

Property Initialization

Initialization Order

Delaying Initialization

Late initialization

Lazy initialization

For the More Curious: Initialization Gotchas

Challenge: The Riddle of Excalibur

14. Inheritance

Defining the Room Class

Creating a Subclass

Type Checking

The Kotlin Type Hierarchy

Type casting

Smart casting

For the More Curious: Any

15. Objects

The object Keyword

Object declarations

Object expressions

Companion objects

Nested Classes

Data Classes

toString

equals

copy

Destructuring declarations

Enumerated Classes

Operator Overloading

Exploring the World of NyetHack

For the More Curious: Defining Structural Comparison

For the More Curious: Algebraic Data Types

Challenge: “Quit” Command

Challenge: Implementing a World Map

Challenge: Ring the Bell

16. Interfaces and Abstract Classes

Defining an Interface

Implementing an Interface

Default Implementations

Abstract Classes

Combat in NyetHack

17. Generics

Defining Generic Types

Generic Functions

Multiple Generic Type Parameters

Generic Constraints

vararg and get

in and out

For the More Curious: The reified Keyword

18. Extensions

Defining Extension Functions

Defining an extension on a superclass

Generic Extension Functions

Extension Properties

Extensions on Nullable Types

Extensions, Under the Hood

Extracting to Extensions

Defining an Extensions File

Renaming an Extension

Extensions in the Kotlin Standard Library

For the More Curious: Function Literals with Receivers

Challenge: toDragonSpeak Extension

Challenge: Frame Extension

19. Functional Programming Basics

Function Categories

Transforms

Filters

Combines

Why Functional Programming?

Sequences

For the More Curious: Profiling

For the More Curious: Arrow.kt

Challenge: Reversing the Values in a Map

Challenge: Applying Functional Programming to Tavern.kt

Challenge: Sliding Window

20. Java Interoperability

Interoperating with a Java Class

Interoperability and Nullity

Type Mapping

Getters, Setters, and Interoperability

Beyond Classes

Exceptions and Interoperability

Function Types in Java

21. Building Your First Android Application with Kotlin

Android Studio

Gradle configuration

Project organization

Defining a UI

Running the App on an Emulator

Generating a Character

The Activity Class

Wiring Up Views

Kotlin Android Extensions Synthetic Properties

Setting a Click Listener

Saved Instance State

Reading from the saved instance state

Refactoring to an Extension

For the More Curious: Android KTX and Anko Libraries

22. Introduction to Coroutines

Parsing Character Data

Fetching Live Data

The Android Main Thread

Enabling Coroutines

Specifying a Coroutine with async

launch vs async/await

Suspending Functions

Challenge: Live Data

Challenge: Minimum Strength

23. Afterword

Where to Go from Here

Shameless Plugs

Thank You

A. More Challenges

Leveling Up with Exercism

Glossary

Index

Kotlin Programming: The Big Nerd Ranch Guide by Josh Skeen and David Greenhalgh Copyright © 2018 Big Nerd Ranch, LLC All rights reserved. Printed in the United States of America. This publication is protected by copyright, and permission must be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, contact Big Nerd Ranch, LLC 200 Arizona Ave NE Atlanta, GA 30307 (770) 817-6373 http://www.bignerdranch.com/ book-comments@bignerdranch.com The 10-gallon hat with propeller logo is a trademark of Big Nerd Ranch, LLC. Exclusive worldwide distribution of the English edition of this book by Pearson Technology Group 800 East 96th Street Indianapolis, IN 46240 USA http://www.informit.com The authors and publisher have taken care in writing and printing this book but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of the use of the information or programs contained herein. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals. ISBN-10 013516236X ISBN-13 978-0135162361 First edition, first printing, July 2018 Release E.1.1.1 2

Dedication For Baker, the best little bug. To Rebecca, a driven, patient, beautiful woman, and the reason that this book came to be. To Mom and Dad, for valuing education above all else. — J.S. — D.G. 4

Acknowledgments We received a lot of help in writing this book. Without that help, this book would not be what it is, and it may never even have happened. Thanks are due. First, we need to say thank you to our colleagues at Big Nerd Ranch. Thank you to Stacy Henry and Aaron Hillegass for providing us with the time and space to write this book. It has been immensely gratifying to learn and teach Kotlin. We hope that this book lives up to the trust and the support that we have received. Particular thanks are also due to our colleagues at Big Nerd Ranch. Your careful teaching revealed many bugs in the text, and your thoughtful recommendations led to many improvements in our approach. It is truly wonderful to have colleagues such as you. Thank you Kristin Marsicano, Bolot Kerimbaev, Brian Gardner, Chris Stewart, Paul Turner, Chris Hare, Mark Allison, Andrew Lunsford, Rafael Moreno Cesar, Eric Maxwell, Andrew Bailey, Jeremy Sherman, Christian Keur, Mikey Ward, Steve Sparks, Mark Dalrymple, CBQ, and everyone else at the Ranch who helped us with this work. Our colleagues in operations, marketing, and sales are also instrumental. Classes would literally never be scheduled without their work. Thank you Heather Sharpe, Mat Jackson, Rodrigo "Ram Rod" Perez-Velasco, Nicholas Stolte, Justin Williams, Dan Barker, Israel Machovec, Emily Herman, Patrick Freeman, Ian Eze, and Nikki Porter. We cannot do what we do without what you do. Special thanks and an extra bit of karma are also owed to our amazing students who were adventurous enough to join us for the early access version of the course and were kind enough to help us identify errata. Without your feedback and insights into how to improve the course, this text would not be where it is today. Those students include: Santosh Katta, Abdul Hannan, Chandra Mohan, Benjamin DiGregorio, Peng Wan, Kapil Bhalla, Girish Hanchinal, Hashan Godakanda, Mithun Mahadevan, Brittany Berlanga, Natalie Ryan, Balarka Velidi, Pranay Airan, Jacob Rogers, Jean-Luc Delpech, Dennis Lin, Kristina Thai, Reid Baker, Setareh Lotfi, Harish Ravichandran, Matthew Knapp, Nathan Klee, Brian Lee, Heidi Muth, Martin Davidsson, Misha Burshteyn, Kyle Summers, Cameron Hill, Vidhi Shah, Fabrice Di Meglio, Jared Burrows, Riley Brewer, Michael Krause, Tyler Holland, Gajendra Singh, Pedro Sanchez, Joe Cyboski, Zach Waldowski, Noe Arzate, Allan Caine, Zack Simon, Josh Meyers, Rick Meyers, Stephanie Guevara, Abdulrahman Alshmrani, Robert Edwards, Maribel Montejano, and Mohammad Yusuf. We want to extend a special thank you to our colleagues and members of the Android community who helped us test the book's accuracy, clarity, and ease of use. Without your external perspective, putting this book together would have been even more daunting. Thank you Jon Reeve, Bill Phillips, Matthew Compton, Vishnu Rajeevan, Scott Stanlick, Alex Lumans, Shauvik Choudhary, and Jason Atwood. We also need to acknowledge the many talented folks who worked on the book with us. Elizabeth Holaday, our editor, helped refine the book, crystallize its strengths, and diminish its weaknesses. Anna Bentley, our copyeditor, found and corrected errors and ultimately made us look smarter than we are. Ellie Volckhausen designed the cover. And Chris Loper designed and produced the print book and the EPUB and Kindle versions. Finally, thank you to all our students. Being your teacher offers us the opportunity to be a student in many ways, and for that we are immensely grateful. Teaching is part of the greatest 5

thing that we do, and it has been a pleasure working with you. We hope that the quality of this book matches your enthusiasm and determination. 6

Table of Contents Introducing Kotlin Why Kotlin? Who Is This Book For? How to Use This Book For the More Curious Challenges Typographical conventions Using an eBook Looking Forward 1. Your First Kotlin Application Installing IntelliJ IDEA Your First Kotlin Project Creating your first Kotlin file Running your Kotlin file The Kotlin REPL For the More Curious: Why Use IntelliJ? For the More Curious: Targeting the JVM Challenge: REPL Arithmetic 2. Variables, Constants, and Types Types Declaring a Variable Kotlin’s Built-In Types Read-Only Variables Type Inference Compile-Time Constants Inspecting Kotlin Bytecode For the More Curious: Java Primitive Types in Kotlin Challenge: hasSteed Challenge: The Unicorn’s Horn Challenge: Magic Mirror 3. Conditionals if/else Statements Adding more conditions Nested if/else statements More elegant conditionals Ranges when Expressions String Templates Challenge: Trying Out Some Ranges Challenge: Enhancing the Aura Challenge: Configurable Status Format 4. Functions Extracting Code to Functions Anatomy of a Function Function header Function body 7

Function scope Calling a Function Refactoring to Functions Writing Your Own Functions Default Arguments Single-Expression Functions Unit Functions Named Function Arguments For the More Curious: The Nothing Type For the More Curious: File-Level Functions in Java For the More Curious: Function Overloading For the More Curious: Function Names in Backticks Challenge: Single-Expression Functions Challenge: Fireball Inebriation Level Challenge: Inebriation Status 5. Anonymous Functions and the Function Type Anonymous Functions The function type Implicit returns Function arguments The it keyword Accepting multiple arguments Type Inference Support Defining a Function That Accepts a Function Shorthand syntax Function Inlining Function References Function Type as Return Type For the More Curious: Kotlin’s Lambdas Are Closures For the More Curious: Lambdas vs Anonymous Inner Classes 6. Null Safety and Exceptions Nullability Kotlin’s Explicit Null Type Compile Time vs Runtime Null Safety Exceptions Throwing an exception Custom exceptions Handling exceptions 7. Strings Extracting Substrings substring split Option one: the safe call operator Option two: the double-bang operator Option three: checking whether a value is null with if Preconditions Null: What Is It Good For? For the More Curious: Checked vs Unchecked Exceptions For the More Curious: How Is Nullability Enforced? 8

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