Kotlin - 字符串模版 String_kotlin 字符串模板

String字符串

//使用for循环进行遍历
for (s in str) print(s + ",")  //H,e,l,l,o, ,K,o,t,l,i,n,

增

val str = "Hello Kotlin"
val num = "123456123"
 
println(str + num)    //Hello Kotlin123456123
println(str.plus(Person())) //Hello KotlinPerson{name='Default', age=0}
println(str[1])    //e

删

val str = "Hello Kotlin"
val num = "123456123"
 
println(num.drop(3))          //456123
println(num.substring(3))     //456123
println(num.dropLast(3))      //123456
println(num.substring(0, num.length - 3))  //123456
println(num.dropWhile { it == '1' })       //23456123
println(num.substring(1..3))               //234
 
println(num.take(3))        //123
println(num.takeLast(3))    //123
println(num.takeWhile { it == '1' || it == '2' })   //12
println(num.takeLastWhile { it == '1' })            //结果为空
 
println(str.subSequence(2,4))    //ll
println(str.subSequence(2..4))   //llo
println(str.substring(2))        //llo Kotlin
println(str.substring(2,4))      //ll
println(str.substring(2..4))     //llo

改

val str = "Hello Kotlin"
val num = "123456123"
 
println(str.toUpperCase())  //HELLO KOTLIN
println(str.toLowerCase())  //hello kotlin
println(str.reversed())     //niltoK olleH
 
println(str.replace("Hello", "NiHao"))   //NiHao Kotlin
println(str.replace("hello", "NiHao"))   //Hello Kotlin
println(str.replace("Hello", "NiHao", true))   //NiHao Kotlin
println(str.replace("hello", "NiHao", false))   //Hello Kotlin
println(num.replace('1', '9'))   //923456923
println(num.replace(Regex("[0-9]+"), "a"))
println(num.replaceFirst('2', '9'))  //193456123
println(num.replaceBefore('4', "99"))    //99456123
 
println(num.split('2')) //[1, 34561, 3]

查 

val str = "Hello Kotlin"
val num = "123456123"
 
println(str[6])     //K
println(str.get(6)) //K
 
println(num.first())                //1
println(num.first { it == '4' })    //4
println(num.count())                //9
println(num.length)                 //9
println(num.count { it == '1' })    //2
println(num.startsWith('1'))
 
println(str.indexOf('l'))                //2
println(num.lastIndexOf("23"))           //7
println(str.indexOfFirst { it == 'l' })  //2
println(str.indexOfLast { it =='l' })    //9

字符串模版

//增
var str = "2" + 32   //用 + 操作符连接字符串，第一个元素要是字符串
str += "00"  //字符串拼接
println(str) //打印：23200
 
//改
val aa = "小明和朋友玩得很开心！"
val bb = "小红"
println(aa.replace("朋友", bb))    //打印：小明和小红玩得很开心！
 
//查
val str2 = "今天天气不错"
println(str2[5]) //字符串元素可通过索引拿到，打印：错
for (s in str2) print(s + ",") //遍历
 
//字符串模版
val person = Person("John", 23)
println("姓名：${person.name}，年龄：${person.age}")   //打印：姓名：John，年龄：23
 
val a = 5
val b = 3
println("一共有${a+b}个人")    //打印：一共有8个人
println("$a+$b=${show(5, 3)}") //打印：5+3=8
 
val answer = true
println("答案是：${if(answer)"正确" else "错误"}")    //打印：答案是：正确
 
//打印：映入眼帘的是"紫禁城"3个大字
val place = "紫禁城"
println("映入眼帘的是\"" + place + "\"闪闪的" + place.length + "个大字")    //JAVA拼接方式
println("映入眼帘的是\"$place\"闪闪的${place.length}个大字")                //斜杠转义方式
println("""映入眼帘的是"$place"闪闪的${place.length}个大字""")              //"""原生字符串
println("去${place}玩看到${place.length}个大字")   //去紫禁城玩看到3个大字
 
//打印美元符号
val c = 4.22
println("价格是$$c")   //打印：价格是$4.22
 
//正则表达式
val pattern = """^\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}"""
val email = "google@gmail.com"
 
val regex1 = Regex(pattern) //方式一：构造
val regex2 = pattern.toRegex()  //方式二：扩展函数
 
println(regex1.matches(email))  //精确匹配
println(regex1.containsMatchIn(email))  //包含匹配
 
val str1 = "AB12CD34EF"
val regex3 = Regex("""\d+""")
println(regex3.find(str1)?.value)   //打印：12，返回查找到的第一个匹配的字符串，没找到返回null
regex3.findAll(str1).forEach { e -> print(e.value + ",") }   //打印：12,34, 查找所有匹配的字符串，返回的Sequence是可以迭代的集合，元素类型是MatchResult
println(regex3.replace(str1, "-"))   //打印：AB-CD-EF，替换
println(regex3.split(str1)) //打印：[AB, CD, EF]，若传入limit值表示分割几次就不分割了。默认为0表示符合条件就分割
 
fun show(a: Int, b: Int) = a + b