Category: Kotlin

fun changeTextView(view: View){
        var calendar = Calendar.getInstance()
        val minute = calendar.get(Calendar.MINUTE)

        messageTextView.text = "Hello android!"
        textView.text = minute.toString()
    }

勝手が異なるから、スクリーンショットの転送も最初は一仕事だ。

valは変更不可
varは変更可

getter, setter

class User(var name: String){
  var team = "red"
  get(){
    return field.toUpperCase()
  }

  set(value){
    if (value !=""){
      field = value
    }
  }

  fun sayHi(){
    println("hi $name")
  }
}

fun main(args: Array<String>){
  val tom = User("tom")
  println(tom.team)
  tom.sayHi()
}

class override

class AdminUser(name: String): User(name){
  fun sayHello(){
    println("hello $name")
  }
  override fun sayHi(){
    println("what $name")
  }
}
open class User(var name: String){
  open fun sayHi(){
    println("hi $name")
  }
}

fun main(args: Array<String>){
  val bob = AdminUser("bob")
  println(bob.name)
  bob.sayHi()
}

アクセス修飾子: privateとpublic

open class User(private var name: String){
  open fun sayHi(){
    println("hi $name")
  }
}

class extension

fun User.sayHello(){
  println("hello $name")
}

val User.myName: String
 get() = "I am $name"

class User(var name: String){
  open fun sayHi(){
    println("hi $name")
  }
}

fun main(args: Array<String>){
  val bob = User("bob")
  bob.sayHello()
  bob.sayHi()
  println(bob.myName)
}

抽象クラス

abstract class User {
  abstract fun sayHi()
}
class Japanese: User(){
  override fun sayHi(){
    println("こんにちは")
  }
}
class American: User(){
  override fun sayHi(){
    println("hi")
  }
}

fun main(args: Array<String>){
  val tom = American()
  val taro = Japanese()
  tom.sayHi()
  taro.sayHi()
}

interface

interface Sharable{
  //　抽象プロパティ、抽象メソッド、メソッド
  val version: Double
  fun share()
  fun getInfo(){
    println("Share I/F ($version)")
  }
}
class User: Sharable {
  override val version = 1.1
  override fun share(){
    println("Sharing..")
  }
}

fun main(args: Array<String>){
 val user = User()
 user.share()
 user.getInfo()
}

generics

class MyData<T> {
  fun getThree(x: T){
    println(x)
    println(x)
    println(x)
  }
}

fun main(args: Array<String>){
  val i = MyData<Int>()
  i.getThree(32)

  val s = MyData<String>()
  s.getThree("hello")
}

データクラス

data class Point(val x: Int, val y: Int)

fun main(args: Array<String>){
  val p1 = Point(3, 5)
  val p2 = Point(3, 5)
  val p3 = p1.copy()

  println(p1)
  println(if (p1 == p2) "same" else "not same")
}

List

fun main(args: Array<String>){
  val sales: List<Int> = listOf(20, 30, 40)
  println(sales[1])
  println(sales.size)
  for (sale in sales){
    println(sale)
  }
}

set

fun main(args: Array<String>){
  val answers: Set<Int> = setOf(3, 5, 8, 3)
  println(answers)
  println(answers.contains(3))

  val set1 = setOf(1, 3, 5, 8)
  val set2 = setOf(3, 5, 8, 9)

  println(set1.intersect(set2))
  println(set1.union(set2))
  println(set1.subtract(set2))
}

Map

fun main(args: Array<String>){
  val users: Map<String, Int> = mapOf("kobayashi" to 10, "kagawa" to 22, "tanaka" to 33)
  println(users["kobayashi"])
  println(users.size)
  println(users.keys)
  println(users.values)
  println(users.entries)
}

map, filter, foreach

fun main(args: Array<String>){
  val prices = listOf(53.2, 48.2, 32.8)
  prices 
   /*.map { n -> n + 1.08} //*/
   .map { it * 1.08 }
   .filter { it > 50 }
   .forEach { println(it) }
}

例外処理

fun div(a: Int, b: Int){
  try {
    println(a / b)
  } catch(e: ArithmeticException) {
   println(e.message)
  }
}

fun main(args: Array<String>){
  div(3, 0)
}

Nullable型

fun main(args: Array<String>){
  val s: String? = null
  /*println(s)*/

  /*if (s != null){
    println(s.length)
  } else {
    println(null)
  }*/
  println(s?.length ?: -1)
}

変数

fun main(args: Array<String>){
  val msg: String = "Hello World"
  println(msg)
}

データ型

  val msg: String = "Hello World"
  val c: Char = 'a'
  val i: Int = 100
  val l: Long = 555555555555L
  val d: Double = 234.352
  val f: Float = 123.345
  val flag: Boolean = true

データ演算

val x = 10
  println(x / 3)
  println(x / 3.0)
  println(x % 3)
  var y = 5
  y++
  y--
  println(y)
  var z = 4
  z += 12
  println(z)
  val flag = true
  println(!flag)

文字列

  println("hello " + "world")

  val name = "yoshimoto"
  println("my name is $name")
  println("my score is ${12 + 43}")

  println("hello\n worl\td")

ifの条件分岐

val score = 85
  if (score > 80){
    println("Great!")
  } elseif (score > 60){
      println("good!")
  } else {
    println("soso ..")
  }

when 条件分岐

val num = 3
  when (num){
    0 -> println("zero")
    1 -> println("one")
    in 4.. 10 -> println("many")
    else -> println("other")
  }

while, for

var i = 0
  while (i < 10){
    println("loop: $i")
    i++
  }
for (i in 0..9){
    println(i)
  }

関数

fun sayHi(name: String = "tebes", age: Int = 23){
  println("hi! $name ($age)")
}

fun main(args: Array<String>){
  sayHi("tom", 22)
  sayHi()
}

関数の返り値

fun sayHi(): String {
  return "hi!"
}

fun main(args: Array<String>){
  val msg = sayHi()
  println(msg)
}

class

class User {
  var name = "me!"
  fun sayHi(){
    println("hi $name")
  }
}

fun main(args: Array<String>){
  val user = User() //　インスタンス
  println(user.name)
  user.sayHi()
}

コンストラクタ引数

class User(var name: String) { //コンストラクタ引数
  /*var name = name*/
  var team = "red"
  init {
    println("instance created: name: $name, team: $team")
  }
  fun sayHi(){
    println("hi $name")
  }
}

fun main(args: Array<String>){
  val tom = User("tom")
  println(tom.name)
  tom.sayHi()
}

JetBrain社が作った、Javaを簡潔に書けるようにした言語です。JVM、Androidで動くことから、Android開発で人気を博しています。

Kotlin

エディタにKotlinのSyntaxを入れます。

インストールは公式サイトのGettingStarted->Working with the CommandlineよりSDKMAN!をインストールします。

[vagrant@localhost ~]$ curl -s https://get.sdkman.io | bash
[vagrant@localhost ~]$ source "/home/vagrant/.sdkman/bin/sdkman-init.sh"
[vagrant@localhost ~]$ cd kotlin
[vagrant@localhost kotlin]$ sdk version
==== BROADCAST =================================================================
* 15/11/16: Kotlin 1.0.5-2 released on SDKMAN! #kotlin
* 14/11/16: Gradle 3.2 released on SDKMAN! #gradle
* 10/11/16: Grails 3.2.3 released on SDKMAN! #grailsfw
================================================================================
SDKMAN 5.1.7+91
[vagrant@localhost kotlin]$ sdk install kotlin

インストールが終了したら、動作確認しましょう。

[vagrant@localhost kotlin]$ kotlin -version
Kotlin version 1.0.5-2 (JRE 1.8.0_111-b15)
[vagrant@localhost kotlin]$ kotlinc
Welcome to Kotlin version 1.0.5-2 (JRE 1.8.0_111-b15)
Type :help for help, :quit for quit
>>> 1 + 2
3

fun main(args: Array<String>){
  println("Hello World")
}

[vagrant@localhost kotlin]$ kotlinc myapp.kt -include-runtime -d myapp.jar
[vagrant@localhost kotlin]$ ls
myapp.jar  myapp.kt
[vagrant@localhost kotlin]$ java -jar myapp.jar
Hello World