scala学习五：字符串

十、字符串

Scala中的字符串类型实际上是Java String，它本身没有String
Scala中，string是不可变对象，不可修改。如果修改字符串，会产生新的字符串对象

10.1 Scala字符串

创建字符串实例

var greeting = 'Hello World'
var greeting:String = 'Hello World'

如果想创建一个可以修改的字符串，可以使用String Builder 类
+= 增加字符
++= 增加字符串

object NewTest {
  def main(args: Array[String]): Unit = {
    testString()
  }
  def testString() {
    val buf = new StringBuilder
    buf ++= "hello"
    buf += '_'
    buf ++= "word"
    println(buf.getClass.getSimpleName)
    println("buf is : " + buf.toString);
  }
}

StringBuilder
buf is : hello_word

10.2 字符串长度length

  def stringLength() {
    var palindrome = "hello word"
    var len = palindrome.length()
    println("String Length is : " + len)
  }

String Length is : 10

10.3 字符串连接concat

concat和+都可以

    val stringA = "hello"
    val stringB = "word"
    val stringC = stringA + stringB

10.4 创建格式化字符串

String 类中可以使用 printf() 方法来格式化字符串并输出，String format() 方法可以返回 String 对象而不是 PrintStream 对象。

  def stringFormat(): Unit = {
    val floatVar = 12.456
    val intVar = 2000
    val stringVar = "scala入门"
    val fs = printf("浮点型变量为 %f, 整型变量为 %d, 字符串为 %s", floatVar, intVar, stringVar)
    val getChar0 = stringVar.charAt(0)
    val getChar1 = stringVar.charAt(1)
    val getChar = stringVar.charAt(5)
    println(fs)
    print(getChar0, getChar1, getChar)
  }
  
浮点型变量为 12.456000, 整型变量为 2000, 字符串为 scala入门()
入

10.5 字符串的其他用法

更多的请参考 https://www.runoob.com/scala/scala-strings.html
返回指定位置的字符 str.charAt(int index)， index从0开始

 def moreUse(): Unit = {
   val string1 = "helloWord"
   val string2 = "learnScala"
   val compare = string1.compareTo(string2)        //按字典顺序比较两个字符串
   val equal = string1.contentEquals(string2)      //两个字符串是否相等
   val endif = string1.endsWith("ls")              //是否以"ls"结尾
   val idx = string1.indexOf('l')                  // 'l'的第一个index
   val idxs = string1.indexOf('l', 2)              // 从位置2开始，'l'的第一个index
   val stringIdx = string1.indexOf("ll")           // 字符串'll'的index
   val lastIdx = string2.lastIndexOf('a',6)        // string2 index 0到6组成的字符穿，从倒数开始第一个'a'对应的index
   println(s"compare $compare, is equal $equal, string1 is end ls $endif")
   println(s"string1 index of l is $idx, index of l start from index 1 is $idxs, indexOf ll is $stringIdx")
   println(s"lastIdx of string2 from index0 to 7 is $lastIdx")
 }

compare -4, is equal false, string1 is end ls false
string1 index of l is 2, index of l start from index 1 is 2, indexOf ll is 2
lastIdx of string2 from index0 to 7 is 2