travisdachi

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".grader.LegendaryGraderActivity">

    <TextView

travisdachi

interface Grader {
    fun grade(score: Int): String
}

travisdachi

class TypicalGrader : Grader {
    override fun grade(score: Int): String =
            when (score) {
                in 80..100 -> "A"
                in 70..79 -> "B"
                in 60..69 -> "C"
                in 50..59 -> "D"
                in 0..49 -> "F"
                else -> "???"
            }

travisdachi

class SuGrader(val satisfy: Int = 60) : Grader {
    init {
        if (satisfy < 0 || satisfy > 100)
            throw IllegalArgumentException("A satisfy $satisfy is out of score range of 0-100")
    }

    override fun grade(score: Int) = when (score) {
        in satisfy..100 -> "S"
        in 0 until satisfy -> "U"
        else -> "???"

travisdachi

import kotlinx.android.synthetic.main.activity_legendary_grader.*

class LegendaryGraderActivity : AppCompatActivity() {

    var grader: Grader = TypicalGrader()
    val satisfy = 50

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_legendary_grader)

travisdachi

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 24
    buildToolsVersion "24.0.0"

    defaultConfig {
        applicationId "com.travispea.kotlinforandroid101"

travisdachi

public void attack(Target target) {
    attack(target, new Fist());
}

public void attack(Target target, Weapon weapon) {
    attack(target, weapon, 0.1f);
}

public void attack(Target target, Weapon weapon, float critical) {
    //...

travisdachi

fun attack(target: Target, weapon: Weapon = Fist(), critical: Float = 0.1F) {
    //...
}
// <paramName>: <paramType> [= <defaultValue>]

val target = getCurrentTarget()
attack(target)
attack(target, Sword())
attack(target, Bow(), 0.5F)
attack(target = target, critical = 0.9f)

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public static String formatFancy(Date date) {
    String myFancyFormat = ...
    SimpleDateFormat f = new SimpleDateFormat(myFancyFormat);
    return f.format(date);
}

String fancyDate = MyDateUtil.formatFancy(someDate);

travisdachi

fun Date.formatFancy(): String {
    val myFancyFormat = ...
    val f = SimpleDateFormat(myFancyFormat)
    return f.format(this)
}
// fun <receiverType>.<functionName>(): <returnType>

someDate.formatFancy() //call within Kotlin

MyExtnsionsKt.formatFancy(someDate); //call from Java