Option[T]接口

trait Option[T] {
  def isDefined: Boolean
  def get: T
  def getOrElse(t: T): T
}

Option接口有两个子类：Some[T]和None

Map的get方法返回的就是Option接口

scala> val map1 = Map("one" -> 1, "two" -> 2)
map1: scala.collection.immutable.Map[String,Int] = Map(one -> 1, two -> 2)
scala> map1.get("one")
res5: Option[Int] = Some(1)
scala> map1.get("three")
res7: Option[Int] = None

配合模式匹配使用

val map1 = Map("one" -> 1, "two" -> 2)
val res1 = map1.get("three")
val res2 = res1 match {
   case Some(n) => n+1
   case None => 0
}