0
点赞
收藏
分享

微信扫一扫

Kotlin函数默认值完全解析

双井暮色 2022-02-27 阅读 82


简要介绍

Kotlin函数定义时,支持对参数指定默认值,这样就有效减少Java之前定义重载函数的数量.

简要对比如下:

  1. Java函数定义,如果sayHelloTo函数中的lastName可以使用默认值,则需要定义如下两个函数.
public class Person {
public void sayHelloTo(String firstName,String lastName){
System.out.println("Hi,"+firstName+" "+lastName);
}
public void sayHelloTo(String firstName){
sayHelloTo(firstName,"noLastName");
}
}
  1. Kotlin定义如下,只需要一个函数
class Person {
fun sayHelloTo(firstName: String, lastName: String = "noLastName") {
println("Hi,$firstName $lastName")
}
}

Kotlin函数默认值详细规则


  1. 可以采用指定全部参数名和不指定参数名的调用方式,​推荐采用指定参数名的调用方式​(不能指定部分函数参数名,其他的不指定)
    正确样例:
    ​sayHelloTo("Jerry","Aha")​​​​sayHelloTo(firstName = "Jerry",lastName = "Aha")​​ 错误样例:​​sayHelloTo(firstName = "Jerry","Aha")​
  2. 在指定参数名时,所有无默认值参数传入值即可
    样例:​​sayHelloTo(firstName = "Jerry",lastName = "Aha")​
  3. 在不指定参数名时,则需要区分情况:


  • 如果函数定义时,所有具有默认值的参数都在最后,则可以只传入无默认值参数值.
    样例:
    函数定义:​​fun sayHelloTo(firstName: String, lastName: String = "Aha")​​ 正确样例:​​sayHelloTo("Jerry")​
  • 如果函数定义时,具有默认值的参数并不都是在最后面,则必须传入所有参数值.
    样例:
    函数定义:​​fun sayHelloTo(firstName: String, middleName: String = "",lastName: String)​​ 正确样例:​​sayHelloTo("Jerry","","Aha")​​ 错误样例:​​sayHelloTo("Jerry","Aha")​

Demo代码

  1. Person.kt
class Person(
val firstName: String = "Jerry",
val lastName: String = "Yin"
) {
fun sayHello() {
System.out.println("Hi,$firstName $lastName")
}

fun sayHelloTo(firstName: String = "Baby", lastName: String = "Aha") {
System.out.println("Hi,$firstName $lastName")
}
}
  1. Person2.kt
class Person2(
val firstName: String = "Jerry",
val lastName: String
) {
fun sayHello() {
System.out.println("Hi,$firstName $lastName")
}

fun sayHelloTo(firstName: String = "Baby", lastName: String) {
System.out.println("Hi,$firstName $lastName")
}
}
  1. 调用代码:
Person().sayHello()
Person("Jerry1").sayHello()
Person("Jerry2", "Yin2").sayHello()
Person(firstName = "Jerry3").sayHello()
Person(lastName = "Yin4").sayHello()

Person().sayHelloTo()
Person().sayHelloTo("Baby1")
Person().sayHelloTo("Baby2", "Aha2")
Person().sayHelloTo(firstName = "Baby3")
Person().sayHelloTo(lastName = "Aha4")

Person2(lastName = "Yin5").sayHello()
Person2("Jerry6", "Yin6").sayHello()
Person2("", "").sayHelloTo(lastName = "Yin8")
Person2("", "").sayHelloTo("Jerry9", "Yin9")

点击关注专栏,查看最新技术分享

更多技术总结好文,请关注:「程序园中猿」

Kotlin函数默认值完全解析_默认值Kotlin函数默认值完全解析_javascript_02

举报

相关推荐

0 条评论