Kotlin-Bootcamp-for-Programmers-Udacity

Documentation

Software

JAVA JDK 12.0.1
IntelliJ IDEA Ultimate

Course Outline

Lesson 1: Introduction => Set up Software

Kotlin REPL < Ctrl + Enter > to execute

fun printHello () {
   println ("Hello World")
}

printHello() // Hello World

Lesson 2: Kotlin Basics => Kotlin Koans (REPL) => Operators /

Operators

// res case: kotlin.Type = ?

1+1 // 2

53-3 // 50

50/10 // 5

1/2 // 0

1.0/2.0 // 0.5

6*50 // 300

val fish = 2
fish.times(6) // 12
fish.div(10) // 0
fish.plus(3) // 5
fish.minus(3) // -1

// use primitive 'int' as an object
1.toLong() // 1

val boxed: Number = 1
boxed.toLong() // 1

// aquarium
val aquarium = 1
aquarium // 1

aquarium = 2 // error: val cannot be reassigned => aquarium = 2

var fish = 2
fish // 2

fish = 50
fish // 50

fish = "Bubbles" // error: type mismatch: inferred type is String but Int was expected => fish = "Bubbles"

val plants = 5
val fish = 2
fish + plants // 7

val b: Byte = 1
val i: Int = b // error: type mismatch: inferred type is Byte but Int was expected => val i: Int = b

val i: Int = b.toInt()

val oneMillion = 1_000_000
val socialSecurityNumber = 999_99_9999L
val hexBytes = 0xFF_EC_DE_5E
val bytes = 0b11010010_01101001_10010100_10010010

var rock : Int = null // error: null can not be a value of a non-null type Int => var rock : Int = null

var marbles : Int? = null
var lostOfFish: List<String?> = listOf(null, null)
var everMoreFish : List<String>? = null
var definitelyFish : List<String?>? = null
definitelyFish = listOf(null, null)

// Error
goldfish!!.eat()
goldfish = null
goldfish!!.eat() 

var fishFoodTreats = 5
return fishFoodTreats?.dec() ?: 0

Strings

"Hello Fish" // Hello Fish

"hello" + " fish" // hello fish

val numberOfFish = 5
val numberOfPlants = 12

"I have $numberOfFish fish and $numberOfPlants plants" // I have 5 fish and 12 plants

"I have ${numberOfFish + $numberOfPlants} fish and plants" // I have 17 fish and plants

var fish = "fish"
var plant = "plant"
fish == plant // false
fish == fish // true
fish != plant // true

val numberOfFish = 50
val numberOfPlants = 23
if (numberOfFish > numberOfPlants) println("Good ratio!")
else println("unhealthy ratio")
// Good ratio!

val fish = 50
if (fish in 1..100) println(fish) // 50

when (numberOfFish) {
   0 -> println("Empty tank")
   50 -> println("Full tank")
   else -> println("Perfect!")
}
// Full tank

Arrays and Loops

val myList = mutableListOf("tuna","salmon",shark)
myList = mutableListOf("Koi", "goldfish") // error

val myList = mutableListOf("tuna","salmon",shark)
myList.remove("shark") // true

var fish = 12
var plants = 5
val swarm  = listOf(fish, plants)
swarm // kotlin.collections.List<kotlin.Int> = [12, 5]

val school = arrayOf("tuna","salmon","shark")
val numbers = intArrayOf(1,2,3)

import java.util.*
println(Arrays.toString(intArrayOf(2, "foo"))) // error: type mismatch: inferred type is String but Int was expected

val mix = arrayOf("fish", 2)
println(Arrays.toString(mix)) // [fish, 2]

val bigSwarm  = arrayOf(swarm, arrayOf("dolphin","whale","orka"))
println(Arrays.toString(bigSwarm)) // [[12, 5], [Ljava.lang.String;@43e7ca6f]

val array = Array(5) { it * 2 }
println(array.asList()) // [0, 2, 4, 6, 8]

for (element in swarm) println(element) // 125

for ((index, element) in swarm.withIndex()) {
   println("Fish at $index is $element")
} // Fish at 0 is 12Fish at 1 is 5

Lesson 3: Functions => Run -> Edit Configurations -> Program arguments -> Kotlin

Main Arguments

fun main(args: Array<String>) {
   println("Hello, world!")
}

fun main(args: Array<String>) {
   println("Hello ${args[0]}!")

   val isUnit = print("The is an expression")
   println(isUnit)

   val temperature = 10
   val isHot = if (temperature > 50) true else false
   println(isHot)

   val message = "You are ${if (temperature > 50) "tried" else "safe" } fish"
   println(message)
}

Random Day

import java.util.*

fun main(args: Array<String>) {
   println("Hello ${args[0]}!")
   feedTheFish()
}

fun feedTheFish() {
   val day = randomDay()
   val food = "pellets"
   println("Today is $day and the fish eat $food")
}

fun randomDay(): String {
   val week = listOf("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
   return week[Random().nextInt(7)]
}

Fish Food

import java.util.*

fun main(args: Array<String>) {
   println("Hello ${args[0]}!")
   feedTheFish()
}

fun feedTheFish() {
   val day = randomDay()
   val food = fishFood(day)
   println("Today is $day and the fish eat $food")
}

fun fishFood(day: String): String {
   var food = "fasting"

   return when (day) {
      "Monday" -> "flakes"
      "Wednesday" -> "redworms"
      "Thursday" -> "granules"
      "Friday" -> "mosquitoes"
      "Sunday" -> "plankton"
      else -> "fasting"
   }
}

Changing Water

import java.util.*

fun main(args: Array<String>) {
   println("Hello ${args[0]}!")
   feedTheFish()
}

fun feedTheFish() {
   val day = randomDay()
   val food = fishFood(day)
   println("Today is $day and the fish eat $food")

   shouldChangeWater(day,20,50)
   shouldChangeWater(day)
   shouldChangeWater(day, dirty = 50)
   shouldChangeWater2(day = "Monday")

   if (shouldChangeWater(day)) {
      println("Change the water today")
   }
}

fun shouldChangeWater(
      day: String,
      temperature: Int = 22,
      dirty: Int = 20) : Boolean {
   return true
}

fun shouldChangeWater2(
      temperature: Int = 22,
      dirty: Int = 20,
      day: String) {
}


fun fishFood(day: String): String {
   var food = "fasting"

   return when (day) {
      "Monday" -> "flakes"
      "Wednesday" -> "redworms"
      "Thursday" -> "granules"
      "Friday" -> "mosquitoes"
      "Sunday" -> "plankton"
      else -> "fasting"
   }
}

fun randomDay(): String {
   val week = listOf("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
   return week[Random().nextInt(7)]
}

Compact Functions

import java.util.*

fun main(args: Array<String>) {
   println("Hello ${args[0]}!")
   feedTheFish()

   var bubbles = 0
   while (bubbles < 50) {
      bubbles++
   }

   repeat(2) {
      println("A fish is swimming")
   }
}

fun feedTheFish() {
   val day = randomDay()
   val food = fishFood(day)
   println("Today is $day and the fish eat $food")

   shouldChangeWater(day,20,50)
   shouldChangeWater(day)
   shouldChangeWater(day, dirty = 50)

   if (shouldChangeWater(day)) {
      println("Change the water today")
   }
}

fun getDirtySensorReading() = 20

fun shouldChangeWater(
      day: String,
      temperature: Int = 22,
      dirty: Int = getDirtySensorReading()) : Boolean {

   val isTooHot = temperature > 30
   val isDirty = dirty > 30
   val isSunday = day == "Sunday"

   return when {
      isTooHot(temperature) -> true
      isDirty(dirty) -> true
      isSunday(day) -> true
      else -> false
   }
}

fun isTooHot(temperature: Int) = temperature > 30

fun isDirty(dirty: Int) = dirty > 30

fun isSunday(day: String) = day == "Sunday"

fun fishFood(day: String): String {
   var food = "fasting"

   return when (day) {
      "Monday" -> "flakes"
      "Wednesday" -> "redworms"
      "Thursday" -> "granules"
      "Friday" -> "mosquitoes"
      "Sunday" -> "plankton"
      else -> "fasting"
   }
}

fun randomDay(): String {
   val week = listOf("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
   return week[Random().nextInt(7)]
}

fun makeNewAquarium() = println("Building a new aquarium......")

fun aquariumStatusReport(aquarium: Any = makeNewAquarium()){

}

Kotlin Filters

import java.util.*

fun main(args: Array<String>) {
   println("Hello ${args[0]}!")
   feedTheFish()
   eagerExample()
}

fun eagerExample() {
   val decorations = listOf("rock", "pagoda", "plastic plant", "alligator", "flowerpot")

   val eager = decorations.filter { it[0] == 'p' }
   println(eager)

   // apply filter lazily
   val filtered = decorations.asSequence().filter { it[0] == 'p' }
   println(filtered)
   println(filtered.toList())

   val lazyMap = decorations.asSequence().map {
      println("map: $it")
      it
   }

   println(lazyMap)
   println("first: ${lazyMap.first()}")
   println("all: ${lazyMap.toList()}")
}

fun feedTheFish() {
   val day = randomDay()
   val food = fishFood(day)
   println("Today is $day and the fish eat $food")

   shouldChangeWater(day,20,50)
   shouldChangeWater(day)
   shouldChangeWater(day, dirty = 50)

   if (shouldChangeWater(day)) {
      println("Change the water today")
   }
}

fun getDirtySensorReading() = 20

fun shouldChangeWater(
      day: String,
      temperature: Int = 22,
      dirty: Int = getDirtySensorReading()) : Boolean {

   val isTooHot = temperature > 30
   val isDirty = dirty > 30
   val isSunday = day == "Sunday"

   return when {
      isTooHot(temperature) -> true
      isDirty(dirty) -> true
      isSunday(day) -> true
      else -> false
   }
}

fun isTooHot(temperature: Int) = temperature > 30

fun isDirty(dirty: Int) = dirty > 30

fun isSunday(day: String) = day == "Sunday"

fun fishFood(day: String): String {
   var food = "fasting"

   return when (day) {
      "Monday" -> "flakes"
      "Wednesday" -> "redworms"
      "Thursday" -> "granules"
      "Friday" -> "mosquitoes"
      "Sunday" -> "plankton"
      else -> "fasting"
   }
}

fun randomDay(): String {
   val week = listOf("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
   return week[Random().nextInt(7)]
}

fun makeNewAquarium() = println("Building a new aquarium......")

fun aquariumStatusReport(aquarium: Any = makeNewAquarium()){

}

Kotlin Lambdas

import java.util.*

fun main(args: Array<String>) {
   println("Hello ${args[0]}!")
   feedTheFish()
   eagerExample()
}

// Run REPL
/*
{ println("Hello") }()
val swim = {println("swim \n")}
swim()
*/

fun swim() {
   // swim
}

fun eagerExample() {
   val decorations = listOf("rock", "pagoda", "plastic plant", "alligator", "flowerpot")

   val eager = decorations.filter { it[0] == 'p' }
   println(eager)

   // apply filter lazily
   val filtered = decorations.asSequence().filter { it[0] == 'p' }
   println(filtered)
   println(filtered.toList())

   val lazyMap = decorations.asSequence().map {
      println("map: $it")
      it
   }

   println(lazyMap)
   println("first: ${lazyMap.first()}")
   println("all: ${lazyMap.toList()}")
}

fun feedTheFish() {
   val day = randomDay()
   val food = fishFood(day)
   println("Today is $day and the fish eat $food")

   shouldChangeWater(day,20,50)
   shouldChangeWater(day)
   shouldChangeWater(day, dirty = 50)

   if (shouldChangeWater(day)) {
      println("Change the water today")
   }
}

fun getDirtySensorReading() = 20

fun shouldChangeWater(
      day: String,
      temperature: Int = 22,
      dirty: Int = getDirtySensorReading()) : Boolean {

   val isTooHot = temperature > 30
   val isDirty = dirty > 30
   val isSunday = day == "Sunday"

   return when {
      isTooHot(temperature) -> true
      isDirty(dirty) -> true
      isSunday(day) -> true
      else -> false
   }
}

fun isTooHot(temperature: Int) = temperature > 30

fun isDirty(dirty: Int) = dirty > 30

fun isSunday(day: String) = day == "Sunday"

fun fishFood(day: String): String {
   var food = "fasting"

   return when (day) {
      "Monday" -> "flakes"
      "Wednesday" -> "redworms"
      "Thursday" -> "granules"
      "Friday" -> "mosquitoes"
      "Sunday" -> "plankton"
      else -> "fasting"
   }
}

fun randomDay(): String {
   val week = listOf("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
   return week[Random().nextInt(7)]
}

fun makeNewAquarium() = println("Building a new aquarium......")

fun aquariumStatusReport(aquarium: Any = makeNewAquarium()){

}

var dirty = 20

val waterFilter: (Int) -> Int = { dirty -> dirty/2 }
fun feedFish(dirty: Int) = dirty + 10

fun updateDirty(dirty: Int, operation: (Int) -> Int): Int {
   return operation(dirty)
}

fun dirtyProcessor() {
   dirty = updateDirty(dirty, waterFilter)
   dirty = updateDirty(dirty, ::feedFish)
   dirty = updateDirty(dirty, { dirty -> dirty + 50 })
}

// REPL
/*
val list = listOf(1, 2, 3)
list.filter { it == 2 }
*/

NLGRF/Kotlin-Bootcamp-for-Programmers-Udacity

Kotlin-Bootcamp-for-Programmers-Udacity

Documentation

Software

Course Outline