1.apply函数详解  

1.1. DSL

/*** 为什么要传入扩展函数(泛型),而不是一个普通的匿名函数* T.()->Unit* 扩展函数里自带了接收者对象的this隐式调用* 为什么是泛型的扩展函数?* 因为是由this 隐式调用 this 类型就是泛型类型， 相当于this的扩展函数，就把this的作用域放进去了.** 匿名函数，也可以是扩展函数***/

2.函数式编程

 3.变换函数

3.1 map函数

 

fun main() {val animals:List<String> = listOf("zebra", "giraffe", "elephant", "rat")val map:List<String> = animals.map { animals -> "A baby $animals" } //相当于stream流 map 然后自动collectListprintln(animals)//不会改变原来的集合println(map)
}

 3.2 flapMap

fun main() {val flatMap =listOf(listOf(1, 2, 3), listOf(4, 5, 6, 7, 8, 9)).flatMap { it -> it.map { it + 1 } } //flatMap是合并泛型里同类型的集合println(flatMap)}

3.3 filter

和Java一样，不需要过多重复

3.4 合并函数

zip

fun main() {val employees = listOf("Jack", "Rose", "Jason")val shirtSize = listOf("red", "green", "yellow")val map:Map<String,String> = employees.zip(shirtSize).toMap()println(map)
}

fold

 

fun main() {//将每个元素乘以三叠加起来val fold = listOf(1, 2, 3, 4).fold(0) { acc, i ->println("acc = $acc")acc + (i * 3)}println("sum = $fold")}

4.序列

none 是 若有一个为 true 则为false ，全为false 则为true

fun Int.isPrime():Boolean{( 2 until this).map {if (this % it == 0){return false}}return true
}fun main() {//假定0-5000之内，可以找到1000个素数val toList = (1..5000).toList().filter { it.isPrime() }.take(1000)//take 拿去前1000个println(toList)//就是不知道有多少个可变的序列val oneTousandPrimes = generateSequence(2) { v ->v + 1}.filter { it.isPrime() }.take(1000)println(oneTousandPrimes.toList().size)}

 5. Java与Kotlin互操作性和可空性

package javahuixangfun main() {val adversary = Jhava()val determineGreeting = adversary.determineGreeting()//String! 平台类型  有可能会有空指针 ，需要处理一下println(determineGreeting?.toLowerCase())
}

package javahuixang;public class Jhava {public String utterGreeting(){return "Hello";}public String determineGreeting(){return null;}}

6.类型映射

package javahuixang;public class Jhava {public int hitPoints = 3322;public String utterGreeting(){return "Hello";}public String determineGreeting(){return null;}}

package javahuixangfun main() {val jhava = Jhava()println(jhava.hitPoints.javaClass)
}

7.属性访问

 

package javahuixangfun main() {val jhava = Jhava()println(jhava.hitPoints)
}

package javahuixang;public class Jhava {private int hitPoints = 3322;public String utterGreeting(){return "Hello";}public String determineGreeting(){return null;}public int getHitPoints() {System.out.println("get");return hitPoints;}public void setHitPoints(int hitPoints) {this.hitPoints = hitPoints;}
}

8.Java调用kotlin

package javahuixangfun main() {val adversary = Jhava()val determineGreeting = adversary.determineGreeting()//String! 平台类型  有可能会有空指针 ，需要处理一下println(determineGreeting?.toLowerCase())
}fun makeProclamation() = "Greetings,beast!"

   public static void main(String[] args) {String s = HeroKt.makeProclamation();System.out.println(s);}

9.@file:JvmName 给kotlin文件起别名

@file:JvmName("Hero")
package javahuixang
fun main() {val adversary = Jhava()val determineGreeting = adversary.determineGreeting()//String! 平台类型  有可能会有空指针 ，需要处理一下println(determineGreeting?.toLowerCase())
}fun makeProclamation() = "Greetings,beast!"

 public static void main(String[] args) {String s = Hero.makeProclamation();System.out.println(s);}

10.@JvmField

package javahuixangclass Spellbook{@JvmFieldval spells = listOf("a","b")}

  public static void main(String[] args) {Spellbook spellbook = new Spellbook();//加了  @JvmField 自动调用 kotlin的get方法 ，给Java提供了Kotlin的语法List<String> spells = spellbook.spells;}

11.@JvmOverload

@JvmOverloads
fun handOverFood(leftHand:String="berries",rightHand:String = "beef"){println("Mmmm... you hand over some delicious $leftHand and $rightHand")
}

 public static void main(String[] args) {//Java要支持 用默认值 得重载Hero.handOverFood();}

kotlin最大的优势就是可以和Java互编

12. @JvmStatic

package javahuixangclass Spellbook{@JvmFieldval spells = listOf("a","b")companion object{@JvmFieldval MX=10@JvmStaticfun getSpellGreeting() = println("i am a good")}}

    public static void main(String[] args) {//Java要支持 用默认值 得重载
//        Spellbook.Companion.getMX();System.out.println(Spellbook.MX);//让JAVA支持kotlin的写法Spellbook.getSpellGreeting();}

类加载就加载出来的，在JVM加载不会有线程安全问题

13.Throws

 Kotlin抛出的异常，让JAVA能够catch到

 想要Java 能够catch kotlin 抛出的异常，必须用 这个注解

@kotlin.jvm.Throws(IOException::class)
fun acceptApology() {throw IOException()
}

Java 

  try {Hero.acceptApology();} catch (IOException e) {System.out.println("catch");}

14.函数类型操作

 Java调用kotlin 匿名函数

val translator= {utterance:String ->println(utterance.toLowerCase().capitalize())
}

    public static void main(String[] args) {Function1<String, Unit> translator = Hero.getTranslator();translator.invoke("TRUCE");}