一、let 扩展函数
let.kt文件代码
fun main() {
println("isEmpty = $isEmpty")
printNonNull(null)
printNonNull("my string")
printIfBothNonNull("First","Second")
//下面是运行结果
//test
//isEmpty = false
//Printing "null":
//Printing "my string":
// my string
//
//First : Second
}
val isEmpty = "test".let {
println(it) // 2
it.isEmpty()
}
fun printNonNull(str:String?){
println("Printing \"$str\":")
str?.let {
print("\t")
println(it)
println()
}
}
fun printIfBothNonNull(strOne: String?, strTwo: String?) {
strOne?.let { firstString ->
strTwo?.let { secondString ->
println("$firstString : $secondString")
println()
}
}
}
二、run 扩展函数
run.kt文件代码
fun getNullableLength(ns: String?) {
println("for \"$ns\":")
val resutl = ns?.run {
println("\tis empty? " + isEmpty())
println("\tlength = $length")
length
}//返回最后一行
println("resutl = $resutl")
}
fun main(){
getNullableLength(null)
getNullableLength("")
getNullableLength("some string with Kotlin")
//下面是运行结果
//for "null":
//resutl = null
//for "":
// is empty? true
// length = 0
//resutl = 0
//for "some string with Kotlin":
// is empty? false
// length = 23
//resutl = 23
}
三、with函数
with.kt文件代码
fun main() {
val personal = Personal("test", 20)
val withResult = with(personal) {
println("name = $name")
println("age = $age")
21
22
}
println("withResult = $withResult")
//name = test
//age = 20
//withResult = 22
}
class Personal(var name: String, var age: Int)
四、apply扩展函数
apply.kt文件代码
fun main() {
val jake = Person()
val stringDescription = jake.apply {
name = "Jake"
age = 30
about = "Android developer"
}.toString()
println("stringDescription = $stringDescription")
//stringDescription = Person(name=Jake, age=30, about=Android developer)
}
class Person() {
var name: String? = null
var age: Int = 20
var about: String? = null
override fun toString(): String {
return "Person(name=$name, age=$age, about=$about)"
}
}
五、also扩展函数
also.kt文件代码
fun main() {
val jake = Person2().also {
println(it)
}
getPerson().also {
it.token?.let { tempToen -> login(tempToen) }
}
}
class Person2(
var name: String = "test",
var age: Int = 0,
var about: String? = null
) {
var token: String? = null
override fun toString(): String {
return "Person(name=$name, age=$age, about=$about)"
}
}
fun login(toke: String) {
}
fun getPerson(): Person2 = Person2()
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