Scala学习笔记（五）—— 映射、元祖、集合

1. 映射

映射Java中的Map，即Key/Value的数据形式

• 映射的创建，有以下两种方法

  1 scala> val map =Map("Lisa" -> 90 , "Hellen" -> 89)
  2 map: scala.collection.immutable.Map[String,Int] = Map(Lisa -> 90, Hellen -> 89)
  3 
  4 
  5 scala> val map =Map("Lisa" -> 90 , "Hellen" -> 89)
  6 map: scala.collection.immutable.Map[String,Int] = Map(Lisa -> 90, Hellen -> 89)

•  映射内容的修改

  　　scala中的映射分为可变和不可变的，由import的包决定；默认引入scala.collection.immutable.Map的包；

  　　scala.collection.immutable.Map是不可变的；不可改变已有的Key值的Value，亦不可增加键值对

   1 scala> map
   2 res44: scala.collection.immutable.Map[String,Int] = Map(Lisa -> 90, Hellen -> 8)
   3 
   4 scala> map("Lisa") =100
   5 <console>:15: error: value update is not a member of scala.collection.immutable
   6 Map[String,Int]
   7        map("Lisa") =100
   8        ^
   9 
  10 scala> map("Bob") =100
  11 <console>:15: error: value update is not a member of scala.collection.immutable
  12 Map[String,Int]
  13        map("Bob") =100

  　scala.collection.mutable.Map这个包的Map是可变的；

   1 scala> import scala.collection.mutable.Map
   2 import scala.collection.mutable.Map
   3 
   4 scala> val map2 = Map("Lisa"-> 95,"Helln"-> 85)
   5 map2: scala.collection.mutable.Map[String,Int] = Map(Lisa -> 95,Helln -> 85)
   6 
   7 scala> map2("Lisa")=100
   8 
   9 scala> map2
  10 res49: scala.collection.mutable.Map[String,Int] = Map(Lisa -> 100,Helln -> 85)
  11 
  12 scala> map2 += ("Bob" -> 65)
  13 res50: map2.type = Map(Bob -> 65, Lisa -> 100, Helln -> 85)
  14 
  15 scala> map2 += (("Bob",80))
  16 res52: map2.type = Map(Bob -> 80, Lisa -> 100, Helln -> 85)

   getOrElse(Key，defaultValue)，取Map中的相应的Key的Value值，若不存在，则返回默认值；值得注意的是并没有在Map的添加该记录

  1 scala> map2.getOrElse
  2 getOrElse   getOrElseUpdate
  3 
  4 scala> map2.getOrElse("Alice",60)
  5 res53: Int = 60
  6 
  7 scala> map2
  8 res54: scala.collection.mutable.Map[String,Int] = Map(Bob -> 80, Lisa -> 100, Helln -> 85)