7. 字符串的常用操作

一，字符串查找

1. 获取第一个元素

first()

val str = "Kotlin Good"
val letter = str.first()
println("letter is $letter")

firstOrNull()

val str = ""
val letter = str.firstOrNull()
println("letter is $letter")

2. 获取最后一个元素

last()

val str = "Kotlin"
val letter = str.last()
println("letter is $letter")

lastOrNull

val str = ""
val letter = str.lastOrNull()
println("letter is $letter") // null

3. 查找元素

二，字符串截取

subString()

val str = "Hello Kotlin"
val value = str.substring(0,5)
println(value) // hello

subSequence()

val str = "Hello Kotlin"
val value = str.subSequence(0,8)
println(value) // Hello Ko

4. 字符串替换

replace()

replaceFirst()

replaceBefore()

replaceBeforeLast()

replaceAfter()

replaceAfterLast()

4. 字符串分隔

split()