Head First Kotlin A Brain Friendly Guide 1st Edition by Dawn Griffiths, David Griffiths ISBN 9781491996690 1491996692

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Product details:
ISBN 10: 1491996692
ISBN 13: 9781491996690
Author: Dawn Griffiths, David Griffiths

Head First Kotlin A Brain Friendly Guide 1st Edition Table of contents:

1. getting started: A Quick Dip

Welcome to Kotlinville

It’s crisp, concise and readable

You can use object-oriented AND functional programming

The compiler keeps you safe

You can use Kotlin nearly everywhere

Java Virtual Machines (JVMs)

Android

Client-side and server-side JavaScript

Native apps

What we’ll do in this chapter

Install IntelliJ IDEA (Community Edition)

Let’s build a basic application

1. Create a new project

2. Specify the type of project

3. Configure the project

You’ve just created your first Kotlin project

Add a new Kotlin file to the project

Anatomy of the main function

Add the main function to App.kt

Test drive

What the Run command does

What can you say in the main function?

Loop and loop and loop…

Simple boolean tests

A loopy example

Test drive

Conditional branching

Using if to return a value

Update the main function

Test drive

Code Magnets

Using the Kotlin interactive shell

You can add multi-line code snippets to the REPL

It’s exercise time

Code Magnets Solution

Your Kotlin Toolbox

2. basic types and variables: Being a Variable

Your code needs variables

A variable is like a cup

What happens when you declare a variable

The value is transformed into an object…

…and the compiler infers the variable’s type from that of the object

The variable holds a reference to the object

val vs. var revisited

Kotlin’s basic types

Integers

Floating points

Booleans

Characters and Strings

How to explicitly declare a variable’s type

Declaring the type AND assigning a value

Use the right value for the variable’s type

Assigning a value to another variable

We need to convert the value

An object has state and behavior

How to convert a numeric value to another type

What happens when you convert a value

Watch out for overspill

Store multiple values in an array

How to create an array

Create the Phrase-O-Matic application

Add the code to PhraseOMatic.kt

The compiler infers the array’s type from its values

How to explicitly define the array’s type

var means the variable can point to a different array

val means the variable points to the same array forever…

…but you can still update the variables in the array

Code Magnets

Code Magnets Solution

Your Kotlin Toolbox

3. functions: Getting Out of Main

Let’s build a game: Rock, Paper, Scissors

How the game will work

A high-level design of the game

Here’s what we’re going to do

Get started: create the project

Get the game to choose an option

Create the Rock, Paper, Scissors array

How you create functions

You can send things to a function

You can send more than one thing to a function

Calling a two-parameter function, and sending it two arguments

You can pass arguments to a function so long as the argument type matches the parameter type

You can get things back from a function

Functions with no return value

Functions with single-expression bodies

Create the getGameChoice function

Code Magnets

Code Magnets Solution

Add the getGameChoice function to Game.kt

Behind the scenes: what happens

The story continues

The getUserChoice function

Ask for the user’s choice

How for loops work

Looping through a range of numbers

Use downTo to reverse the range

Use step to skip numbers in the range

Looping through the items in an array

Ask the user for their choice

Use the readLine function to read the user’s input

We need to validate the user’s input

‘And’ and ‘Or’ operators (&& and ||)

Not equals (!= and !)

Use parentheses to make your code clear

Add the getUserChoice function to Game.kt

Test drive

We need to print the results

Add the printResult function to Game.kt

Test drive

Your Kotlin Toolbox

4. classes and objects: A Bit of Class

Object types are defined using classes

You can define your own classes

How to design your own classes

Let’s define a Dog class

How to create a Dog object

How to access properties and functions

What if the Dog is in a Dog array?

Create a Songs application

Test drive

The miracle of object creation

How objects are created

What the Dog constructor looks like

Behind the scenes: calling the Dog constructor

Code Magnets

Code Magnets Solution

Going deeper into properties

Behind the scenes of the Dog constructor

Flexible property initialization

How to use initializer blocks

You MUST initialize your properties

How do you validate property values?

The solution: custom getters and setters

How to write a custom getter

How to write a custom setter

The full code for the Dogs project

Test drive

Your Kotlin Toolbox

5. subclasses and superclasses: Using Your Inheritance

Inheritance helps you avoid duplicate code

An inheritance example

What we’re going to do

Design an animal class inheritance structure

Use inheritance to avoid duplicate code in subclasses

What should the subclasses override?

The animals have different property values…

…and different function implementations

We can group some of the animals

Add Canine and Feline classes

Use IS-A to test your class hierarchy

Use HAS-A to test for other relationships

The IS-A test works anywhere in the inheritance tree

We’ll create some Kotlin animals

Declare the superclass and its properties and functions as open

How a subclass inherits from a superclass

How (and when) to override properties

Overriding properties lets you do more than assign default values

How to override functions

The rules for overriding functions

An overridden function or property stays open…

…until it’s declared final

Add the Hippo class to the Animals project

Code Magnets

Code Magnets Solution

Add the Canine and Wolf classes

Which function is called?

Inheritance guarantees that all subclasses have the functions and properties defined in the superclass

Any place where you can use a superclass, you can use one of its subclasses instead

When you call a function on the variable, it’s the object’s version that responds

You can use a supertype for a function’s parameters and return type

The updated Animals code

Test drive

Your Kotlin Toolbox

6. abstract classes and interfaces: Serious Polymorphism

The Animal class hierarchy revisited

Some classes shouldn’t be instantiated

Declare a class as abstract to stop it from being instantiated

Abstract or concrete?

An abstract class can have abstract properties and functions

We can mark three properties as abstract

The Animal class has two abstract functions

How to implement an abstract class

You MUST implement all abstract properties and functions

Let’s update the Animals project

Test drive

Independent classes can have common behavior

An interface lets you define common behavior OUTSIDE a superclass hierarchy

Let’s define the Roamable interface

Interface functions can be abstract or concrete

How to define interface properties

Declare that a class implements an interface…

…then override its properties and functions

How to implement multiple interfaces

How do you know whether to make a class, a subclass, an abstract class, or an interface?

Update the Animals project

Test drive

Interfaces let you use polymorphism

Access uncommon behavior by checking an object’s type

Where to use the is operator

As the condition for an if

In conditions using && and ||

In a while loop

Use when to compare a variable against a bunch of options

The is operator usually performs a smart cast

Use as to perform an explicit cast

Update the Animals project

Test drive

Your Kotlin Toolbox

7. data classes: Dealing with Data

== calls a function named equals

equals is inherited from a superclass named Any

The importance of being Any

The common behavior defined by Any

We might want equals to check whether two objects are equivalent

A data class lets you create data objects

How to create objects from a data class

Data classes override their inherited behavior

The equals function compares property values

Equal objects return the same hashCode value

toString returns the value of each property

Copy data objects using the copy function

Data classes define componentN functions…

…that let you destructure data objects

Create the Recipes project

Test drive

Generated functions only use properties defined in the constructor

Initializing many properties can lead to cumbersome code

Default parameter values to the rescue!

How to use a constructor’s default values

1. Passing values in order of declaration

2. Using named arguments

Functions can use default values too

Overloading a function

Dos and don’ts for function overloading:

Let’s update the Recipes project

The code continued…

Test drive

Your Kotlin Toolbox

8. nulls and exceptions: Safe and Sound

How do you remove object references from variables?

Remove an object reference using null

Why have nullable types?

You can use a nullable type everywhere you can use a non-nullable type

How to create an array of nullable types

How to access a nullable type’s functions and properties

Keep things safe with safe calls

You can chain safe calls together

What happens when a safe call chain gets evaluated

The story continues

You can use safe calls to assign values…

…and assign values to safe calls

Use let to run code if values are not null

Using let with array items

Using let to streamline expressions

Instead of using an if expression…

…you can use the safer Elvis operator

The !! operator deliberately throws a NullPointerException

Create the Null Values project

The code continued…

Test drive

An exception is thrown in exceptional circumstances

You can catch exceptions that are thrown

Catch exceptions using a try/catch

Use finally for the things you want to do no matter what

An exception is an object of type Exception

You can explicitly throw exceptions

try and throw are both expressions

How to use try as an expression

How to use throw as an expression

Code Magnets

Code Magnets Solution

Your Kotlin Toolbox

9. collections: Get Organized

Arrays can be useful…

…but there are things an array can’t handle

You can’t change an array’s size

Arrays are mutable, so they can be updated

When in doubt, go to the Library

List, Set and Map

List – when sequence matters

Set – when uniqueness matters

Map – when finding something by key matters

Fantastic Lists…

…and how to use them

Create a MutableList…

..and add values to it

You can remove a value…

…and replace one value with another

You can change the order and make bulk changes…

…or take a copy of the entire MutableList

Create the Collections project

Test drive

Code Magnets

Code Magnets Solution

Lists allow duplicate values

How to create a Set

How to use a Set’s values

How a Set checks for duplicates

Hash codes and equality

Equality using the === operator

Equality using the == operator

Rules for overriding hashCode and equals

How to use a MutableSet

You can copy a MutableSet

Update the Collections project

Test drive

Time for a Map

How to create a Map

How to use a Map

Create a MutableMap

Put entries in a MutableMap

You can remove entries from a MutableMap

You can copy Maps and MutableMaps

The full code for the Collections project

Test drive

Your Kotlin Toolbox

10. generics: Know Your Ins from Your Outs

Collections use generics

How a MutableList is defined

Understanding collection documentation (Or, what’s the meaning of “E”?)

Using type parameters with MutableList

Things you can do with a generic class or interface

Here’s what we’re going to do

Create the Pet class hierarchy

Define the Contest class

Declare that Contest uses a generic type

You can restrict T to a specific supertype

Add the scores property

Create the addScore function

Create the getWinners function

Create some Contest objects

The compiler can infer the generic type

Create the Generics project

Test drive

The Retailer hierarchy

Define the Retailer interface

We can create CatRetailer, DogRetailer and FishRetailer objects…

…but what about polymorphism?

Use out to make a generic type covariant

Collections are defined using covariant types

Update the Generics project

Test drive

We need a Vet class

Assign a Vet to a Contest

Create Vet objects

Pass a Vet to the Contest constructor

Use in to make a generic type contravariant

Should a Vet ALWAYS accept a Vet?

A generic type can be locally contravariant

Update the Generics project

Test drive

Your Kotlin Toolbox

11. lambdas and higher-order functions: Treating Code Like Data

Introducing lambdas

What we’re going to do

What lambda code looks like

You can assign a lambda to a variable

Execute a lambda’s code by invoking it

What happens when you invoke a lambda

Lambda expressions have a type

The compiler can infer lambda parameter types

You can replace a single parameter with it

Use the right lambda for the variable’s type

Use Unit to say a lambda has no return value

Create the Lambdas project

Test drive

You can pass a lambda to a function

Add a lambda parameter to a function by specifying its name and type

Invoke the lambda in the function body

Call the function by passing it parameter values

What happens when you call the function

You can move the lambda OUTSIDE the ()’s…

…or remove the ()’s entirely

Update the Lambdas project

Test drive

A function can return a lambda

Write a function that receives AND returns lambdas

Define the parameters and return type

Define the function body

How to use the combine function

What happens when the code runs

You can make lambda code more readable

Use typealias to provide a different name for an existing type

Update the Lambdas project

Test drive

Code Magnets

Code Magnets Solution

Your Kotlin Toolbox

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Tags: Dawn Griffiths, Head First Kotlin, Brain Friendly Guide, David Griffiths