学习scala笔记--24 模式匹配

 

 

 

 

模式匹配

 

match{ case v => code}

匹配到一个就终止  不需要类似 java中的 break

 

 

scala> def judeGrade(grade:String){

     | grade match{

     |    case "A" => println("excellent")

     |    case "B" => println("good")

     |    case "C" => println("just so so")

     |    case _ => println(" need study hard")

     | }

     | }

judeGrade: (grade: String)Unit

 

scala> judeGrade("A")

excellent

 

scala> judeGrade("B")

good

 

scala> judeGrade("C")

just so so

 

 

scala> judeGrade("D")

 need study hard

 

scala> judeGrade("E")

 need study hard

 

scala> 

 

 

 

 

case 中可以 使用 if 守卫

 

scala> def judeGrade(grade:String,name:String){

     |  grade match {

     |     case "A" => println("very good")

     |     case "B" => println(" good ")

     |     case "C" => println(" ok ")

     |     case _grade if name=="tom" => println(name + " you need work hard")

     |     case _grade if name=="jam" => println(name + " u also need work hard")

     |     case _ => println(" not vary bad ")

     | }

     | }

judeGrade: (grade: String, name: String)Unit

 

scala> judeGrade("A","")

very good

 

scala> judeGrade("B","")

 good 

 

scala> judeGrade("C","")

 ok 

 

scala> judeGrade("D","")

 not vary bad 

 

scala> judeGrade("D","jeff")

 not vary bad 

 

scala> judeGrade("D","tom")

tom you need work hard

 

scala> judeGrade("D","jam")

jam u also need work hard

 

scala> judeGrade("C","jam")

 

 

 

 

 

 

注意下面的  case _g     使用变量

 

scala> def judeGrade(grade:String,name:String){

     | grade match {

     |      case "A" => println("very good")

     |      case "B" => println(" good ")

     |      case "C" => println(" ok ")

     |      case _grade if name=="tom" => println(name + " you need work hard")

     |      case _grade if name=="jam" => println(name + " u also need work hard")

     |      case _g => println("your grade is "+_g +" not vary bad ")

     | }

     | }

judeGrade: (grade: String, name: String)Unit

 

scala> judeGrade("D","jam")

jam u also need work hard

 

scala> judeGrade("E","jam")

jam u also need work hard

 

scala> judeGrade("E","")

your grade is E not vary bad 

 

scala> judeGrade("F","")

your grade is F not vary bad 

 

 

 

----------------------------------

 

 

 对类型进行匹配

 

  case 变量:类型 => 代码

  

  

  scala> def judeGradeType(v:Any){

     |  v match {

     |   case x : Int => println(" --int--")

     |   case x : String => println("--string--")

     |   case _ => println("--other--")

     | }

     | }

judeGradeType: (v: Any)Unit

 

scala> judeGradeType("Hello")

--string--

 

scala> judeGradeType(123)

 --int--

 

scala> judeGradeType(1.0)

  

----------------------------------

 

匹配 Array

 

scala> def matchArray(arr:Array[Any]){

     | arr match{

     |  case Array(0) => println("0")

     |   case Array(x,y) => println(" x , y")

     |   case _ => println("--")

     |  }

     |  }

matchArray: (arr: Array[Any])Unit

 

scala> matchArray(Array(1,0,2))

--

 

scala> matchArray(Array(0))

0

 

scala> matchArray(Array(x,y))

<console>:13: error: not found: value x

       matchArray(Array(x,y))

                        ^

<console>:13: error: not found: value y

       matchArray(Array(x,y))

                          ^

 

scala> matchArray(Array("x","y"))

 x , y

 

scala> matchArray(Array("x","y","d"))

--

 

 

 

----------------------------------

 

 

匹配 数组以什么开头

 

scala> :paste

// Entering paste mode (ctrl-D to finish)

 

 

def matchArray(arr:Array[Any]){

arr match{

  case Array(0) => println("0")

  case Array(x,y) => println(" x , y")

  case Array(0,_*)=> println(" begin with 0 ")

}

}

 

// Exiting paste mode, now interpreting.

 

matchArray: (arr: Array[Any])Unit

 

scala> matchArray(Array(0,2,4,5))

 begin with 0 

 

 

 ----------------------------------

 

 

 

 

 匹配  List

 

 

scala> :paste

// Entering paste mode (ctrl-D to finish)

 

def matchArray(arr : List[Any]){

 arr match{

case 0 :: Nil => println("0")

case x::y:: Nil => println(x +"" + y)

case 0::tail => println("0....")

case _ => println("other")

}

}

 

// Exiting paste mode, now interpreting.

 

matchArray: (arr: List[Any])Unit

 

scala> matchArray(List(0))

0

 

scala> matchArray(List(0,1,3))

0....

 

scala> matchArray(List("x","y"))

xy

 

scala> matchArray(List("x","y","z"))

other

 

----------------------------------

  

 变量声明中的模式

 

 

 scala> var (x,y)=(1,2)

x: Int = 1

y: Int = 2

 

scala> x

res19: Int = 1

 

scala> y

res20: Int = 2