Option是一个抽象类
None 和 Some 继承Option

sealed abstract class Option[+A]() extends scala.AnyRef with scala.Product with scala.Serializable {

final case class Some[+A](val value : A) extends scala.Option[A] with scala.Product with scala.Serializable {

case object None extends scala.Option[scala.Nothing] with scala.Product with scala.Serializable {

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

object OptionDemo {
  def main(args: Array[String]) {
    val map = Map("a" -> 1, "b" -> 2)
    val value = map.get("a")
    // class scala.Some
    println(value.getClass)
    println(value)

    val value1: Option[Int] = map.get("a")
    println(value1)

    val value3: Int = value1.get
    // int
    println(value3.getClass)
    // 1
    println(value3)

    if (value.isDefined) {
      println(value.get)
    } else {
      println("null")
    }

    val value4 = map.get("a").getOrElse(null);
    // class java.lang.Integer
    println(value4.getClass)
    println(value4)

    val value5 = map.get("c")
    // class scala.None$
    println(value5.getClass)
    // None
    println(value5)
    val value6 = map.get("c").getOrElse(null)
    // println(value6.getClass)
    // null
    println(value6)

    val value7 : Option[Int] = map.get("a")
    val value8 : Some[Int] = null
    val value9 : Any = null
  }
}


isDefined — True if not empty
isEmpty — True if empty
nonEmpty — True if not empty
orElse — Evaluate and return alternate optional value if empty
getOrElse — Evaluate and return alternate value if empty
get — Return value, throw exception if empty
fold — Apply function on optional value, return default if empty
map — Apply a function on the optional value
flatMap — Same as map but function must return an optional value
foreach — Apply a procedure on option value
collect — Apply partial pattern match on optional value
filter — An optional value satisfies predicate
filterNot — An optional value doesn't satisfy predicate
exists — Apply predicate on optional value, or false if empty
forall — Apply predicate on optional value, or true if empty
contains — Checks if value equals optional value, or false if empty
toList — Unary list of optional value, otherwise the empty list