1、lambda 表达式

            //lambda表达式
            val b: (Int) -> Boolean = { it > 0 }
            val c = {x:Int -> x>0}
            val b1: (Int,Int) -> Boolean = { x,y -> x>y }
            println(b(-1))
            println(c(-1))

2、函数式接口

也叫做 SAM （单抽象方法）编程 一个接口一个方法

fun interface IntPredata {
    fun getInt(num: Int): Int
}
 val a = IntPredata { it + 1 }
 println(a.getInt(10))

成员引用

class Child : Person {
    override fun walk() {
        println("child walk")
    }

    override fun speak() {
        println("child speak")
    }

}
//使用::
val b = Child::walk
b(Child())
//使用lambda
val b1 = { c: Child -> c.speak() }
b1(Child())

函数式api

            val list = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9)
            val list2 = list.filter { it % 2 == 0 }
            val list3 = list.map { Child(it) }

回调

java 味道的回调

 interface ClickListener {
    fun onClick();
}

class View {
    lateinit var listener: ClickListener;
    fun setOnClickListener(listener: ClickListener) {
        this.listener = listener;
    }

    fun click() {
        listener.onClick()
    }
}

 val view = View()
            view.setOnClickListener(object : ClickListener {
                override fun onClick() {
                    println("onclick")

                }
            })
view.click()

kotlin 风味

class View2{
    lateinit var listener:(Unit)->Unit
    fun setOnClickListener2(listener:(Unit)->Unit){
        this.listener = listener
    }
    fun click2(){
        listener.invoke(Unit)
    }

}

val view2 = View2()
view2.setOnClickListener2 {
println("onclick2")
}
view2.click2()

更纯正的 利用函数式接口

fun interface ClickListener2{
    fun onClick2()
}
class View2{
    lateinit var listener2:ClickListener2

    fun setOnClickListener22(listener2: ClickListener2){
        this.listener2 = listener2
    }
    fun click2(){
        listener2.onClick2()
    }

}
val view2 = View2()
val listener = ClickListener2{
    println("--------")
}
view2.setOnClickListener22(listener)
view2.click2()

class View2 (val id: Int){
    lateinit var listener2: ClickListener2

    fun setOnClickListener22(listener2: ClickListener2) {
        this.listener2 = listener2
    }

    fun click2() {
        listener2.onClick2(this)
    }

}

fun interface ClickListener2 {
    fun onClick2(view2:View2)
}

val listener = ClickListener2 { view ->
    println(view.id)
}
val view2 = View2(123)
view2.setOnClickListener22(listener)
view2.click2()

类型

null

内联扩展函数

let、with、run、apply、also