Scala中的模式匹配

 作者：林伟兵，叩丁狼教育高级讲师，原创文章，未经同意不得随意转载

在Java中我们可以通过switch..case语句来实现模式匹配，在scala中提供了match case实现模式匹配。

普通的模式匹配语句如下：

val arr = Array("spark","storm","flink","hadoop")
val name = arr(scala.util.Random.nextInt(arr.length))
val tipStr = name match {
  case "spark" => "This is a spark book "
  case "storm" => "This is a storm book "
  case "flink" => "This is a flink book "
  case "hadoop" => "This is a hadoop book "
  case _ => "i don\'t know !"
}
println(tipStr)

除了满足普通的匹配,还可以进行Array匹配，如下代码：

sayHi("",Array("Zhangsan"))
sayHi("lisi",Array("lisi"))

def sayHi(name:String, arr: Array[String]): Unit ={
  arr match {
    case Array("Zhangsan") => println("Hi , zhangsan...")
    case Array(x,y) => println("Hi,"+x + ","+ y)
    case Array("Zhangsan",_*) => println("Hi,Zhangsan and others...")
    case _ if name == "lisi" => println("lisi jun")
    case _ => println("Hi everyones")
  }
}

将上面的匹配换成List,如下代码：

sayHi(List("Zhangsan"))
sayHi(List("lisi","wangwu"))
sayHi(List("Zhangsan","lisi","wangwu"))
sayHi(List("wangwu"))

def sayHi(arr: List[String]): Unit ={
  arr match {
    case "Zhangsan" :: Nil => println("Hi , zhangsan...")
    case x :: y :: Nil => println("Hi,"+x + ","+ y)
    case "Zhangsan":: tail => println("Hi,Zhangsan and others...")
    case _ => println("Hi everyones")
  }
}

也可以对类型进行匹配：

checkType(33)
  checkType("Hello world")
  checkType(15.9f)

def checkType(obj:Any): Unit ={
  obj match {
    case x:Int => println("pass type is Int")
    case x:Double => println("pass type is Double")
    case x:String => println("pass type is String")
    case _ => println("pass type is Others...")
  }
}

捕获多种异常的处理：

try{
  val arr = Array()
  print("arr(11) :"+ arr(11))
}catch {
  case e:ArrayIndexOutOfBoundsException => println("ArrayIndexOutOfBoundsException:"+e.getLocalizedMessage)
  case e:Exception => println("Exception:"+e)
}

模式匹配还支持泛型操作：

class Person(name:String)
case class Teacher(name:String, grade:Int) extends Person(name)
case class Student(name:String, age:Int) extends Person(name)
case class OtherPerson(name:String) extends Person(name)

def doWork(person:Person): Unit ={
  person match {
    case Teacher(name, grade) => println(s"teacher $name is teach in grade $grade")
    case Student(name, age) => println(s"student $name age is $age")
    case _ => println(s"other person is working...")
  }
}

doWork(new Student("张三",22))
doWork(new Teacher("李四", 5))
doWork(new OtherPerson("李四"))

对于map取值来说，Some和None模式匹配：

val map = Map("php" -> 85, "bigdata" -> 99)
val item  = map.get("php")
item match {
  case Some(x) => println("item 是"+ x)
  case None => println("找不到....")