模式匹配「建议收藏」

对值进行模式匹配

   object valueTest{
        def main(args: Array[String]): Unit = {
          def Score(score:String): Unit ={
            score match {
              case "A"=>println("very good")
              case "B"=>println("good")
              case "C"=>println("just soso")
              case other  =>println("terrible")     //默认是_,也可以用其他的变量名
            }
          }
          Score("D")
        }
      }

在模式匹配中使用if守卫：在case后的条件里面再加一个if条件

object valueTest{
      def main(args: Array[String]): Unit = {
        def Score(name:String,score:String): Unit ={
          score match {
            case "A"=>println("very good")
            case "B"=>println("good")
            case "C"=>println("just soso")
            case _ if name=="James"=>print(s"come on !!!  $name")   //if守卫
            case _ =>println("terrible")
          }
        }
        Score("James","F")
      }
    }

在模式匹配中进行变量赋值：如果模式匹配的默认情况为一个变量名xx，则就会将要匹配的值A赋值给这个变量xx，可以在后面的处理语句中使用该值

object valueTest{
      def main(args: Array[String]): Unit = {
        def Score(name:String,score:String): Unit ={
          score match {
            case "A"=>println("very good")
            case "B"=>println("good")
            case "C"=>println("just soso")
            case _ if name=="James"=>print(s"come on !!!  $name")
            case other  =>println("terrible, you just "+other)  //变量赋值
          }
        }
        Score("Jamues","F")
      }
    }

基本语法:变量A match {case 变量: 类型 => 代码}

//变量Excep的数据类型是模式匹配中类型excipn的父类
object ExceptionTest{
  def main(args: Array[String]): Unit = {
    import java.io._
    def funException(Excep: Exception) {
      Excep match {
        case excip1: IllegalArgumentException => println(excip1)
        case excip2: FileNotFoundException => println( excip2)
        case excip3: IOException => println( excip3)
        case _: Exception => println("............" )
      }
    }
    funException(new IOException("..."))
  }
}

object ArrayTest{
  def main(args: Array[String]): Unit = {
    def playBall(arr: Array[Any]) {
      arr match {
        case Array("basketball") => println("play basketball")  //匹配一个元素
        case Array(ball1,(ball2,ball3)) => println("一个单个元素，一个二元组") //匹配特定结构
        case Array("ball", _*) => println("ball start ") //匹配以ball开头
        case _ => println("hey, who are you?")
      }
    }
    playBall(Array("ball"))
  }
}

class Person
case class Teacher(name: String, subject: String) extends Person
case class Student(name: String, classroom: String) extends Person
object MatchTest {
    def main(args: Array[String]): Unit = {
      def judgeIndentity(person: Person): Unit = {
        person match {
          case Teacher(name, subject) => println(s"name = $name, subject = $subject")
          case Student(name, classroom) => println(s"name = $name, classroom = $classroom")
          case _ => println("........................")
        }
      judgeIndentity(Student("xz", "1001"))
    }
  }
}

Option[T]用在模式匹配中用来判断变量是否有值（对有值和无值做不同的处理）

object OptionTest{
  def main(args: Array[String]): Unit = {
    val person = Map(("Tom",15),("Wiki",26))
    val age: Option[Int] = person.get("Toms")
      age match {
        case Some(grade) => println(s" is ${age.get} years")
        case None => println("who are you")
      }
  }
}

object MatchTest {
    def main(args: Array[String]): Unit = {
      // 将列表中字母变成大写
      val list  = List((1, ("aa", 11)), (2, ("bb", 22)), (3, ("cc", 33)))
      list.map(item => (item._1, (item._2._1.toUpperCase, item._2._2)))

      // 模式匹配使代码更具有可读性
      list.map{
        case (id,(na,ages)) =>(id,(na.toUpperCase(),ages))
      }
  }
}