scala学习笔记(十五):模式匹配

阅读更多

   模式匹配在spark中非常重要，你可以在很多地方能看见模式匹配

  

 def main(args: Array[String]): Unit = {
    // trigger the constant patterns
    println(echoWhatYouGaveMe(0))
    println(echoWhatYouGaveMe(true))
    println(echoWhatYouGaveMe("hello"))
    println(echoWhatYouGaveMe(Nil))
    
    println(echoWhatYouGaveMe(List(1,2,3)))
    println(echoWhatYouGaveMe(List(1,2)))
    println(echoWhatYouGaveMe(Vector(1,2,3,4)))
    
    println(echoWhatYouGaveMe((1,2)))
    println(echoWhatYouGaveMe((1,2,3)))
    
    println(echoWhatYouGaveMe(Dogs("kkk")))
    
    println("sum ="+sum(List(1,2,3,4,5)))
    println("multiply ="+multiply(List(1,2,3,4,5)))
    
    println(toInt("11"))
    
    copyFile("D:\\spark.txt", "D:\\spark1.txt")
  }
  
  def echoWhatYouGaveMe(x :Any) = x match {
    //常量匹配 constant patterns
      case 0 => "zero"
      case true => "true"
      case "hello" => "you said 'hello'"
      case Nil => "an empty List"
      
    //序列匹配 sequence patterns
      case List(1,a,b) => s"a three-element list with 0 as the first element second $a three $b"
      case List(1,_*) => "a list beginning with 1, having any number of elements"
      case Vector(1,_*)=> "a vector starting with 1, having any number of elements"
    
    //元组 tuples 
      case (a, b) => s"got $a and $b"
      case (a, b, c) => s"got $a, $b, and $c"
     
    //构造器 constructor patterns 
      case Person(first, "Alexander") => s"found an Alexander, first name = $first"
      case Dogs("Suka") => "found a dog named Suka"
    
    //typed patterns
      case s: String => s"you gave me this string: $s"
      case i: Int => s"thanks for the int: $i"
      case f: Float => s"thanks for the float: $f"
      case a: Array[Int] => s"an array of int: ${a.mkString(",")}"
      case as:Array[String] => s"an array of strings: ${as.mkString(",")}"
      case d: Dogs => s"dog: ${d.name}"
      case list: List[_] => s"thanks for the List: $list"
      case m: Map[_, _] => m.toString
    //default
      case _ => "Unknown"
  }
  //How to use Lists in Scala match expressions List最后一个元素是Nil，所以在case的时候一定要加Nil匹配
  def sum(list:List[Int]):Int = list match{
    case Nil => 0
    case x :: rest => x + sum(rest)
  }
  
  def multiply(list:List[Int]):Int = list match{
    case Nil => 1
    case x :: rest => x * multiply(rest)
  }
  
  //模式匹配最显著的例子就是异常捕捉
  def openAndReadAFile(filename:String) = {
    try {
        val lines = Source.fromFile(filename).getLines()
        for(line <- lines){
          println(line)
        }
    } catch {
      case t: FileNotFoundException => t.printStackTrace() 
      case e: IOException  => println("Had an IOException trying to read that file")
    }
  }