Scala中的模式匹配

本文作者：林伟兵，叩丁狼高级讲师。原创文章，转载请注明出处。

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 grade")
case Student(name, age) => println(s"student 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....")
}

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