Scala学习笔记（五）—— 元组和集合

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

   scala> val map =Map("Lisa" -> 90 , "Hellen" -> 89)
   map: scala.collection.immutable.Map[String,Int] = Map(Lisa -> 90, Hellen -> 89)
  
   scala> val map =Map("Lisa" -> 90 , "Hellen" -> 89)
   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

   scala> map
   res44: scala.collection.immutable.Map[String,Int] = Map(Lisa -> 90, Hellen -> 8)
  
   scala> map("Lisa") =100
   <console>:15: error: value update is not a member of scala.collection.immutable
   Map[String,Int]
          map("Lisa") =100
          ^
  
   scala> map("Bob") =100
   <console>:15: error: value update is not a member of scala.collection.immutable
   Map[String,Int]
          map("Bob") =100

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

   scala> import scala.collection.mutable.Map
   import scala.collection.mutable.Map
  
   scala> val map2 = Map("Lisa"-> 95,"Helln"-> 85)
   map2: scala.collection.mutable.Map[String,Int] = Map(Lisa -> 95,Helln -> 85)
  
   scala> map2("Lisa")=100
  
   scala> map2
   res49: scala.collection.mutable.Map[String,Int] = Map(Lisa -> 100,Helln -> 85)
  
   scala> map2 += ("Bob" -> 65)
   res50: map2.type = Map(Bob -> 65, Lisa -> 100, Helln -> 85)
  
   scala> map2 += (("Bob",80))
   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

   scala> map2.getOrElse
   getOrElse   getOrElseUpdate
  
   scala> map2.getOrElse("Alice",60)
   res53: Int = 60
  
   scala> map2
   res54: scala.collection.mutable.Map[String,Int] = Map(Bob -> 80, Lisa -> 100, Helln -> 85)

2. 元组

映射是K/V对偶的集合，对偶是元组的最简单形式，元组可以装着多个不同类型的值；Map可以看做是装了对偶元组的集合

• 元组的创建

   scala> val y =(1,"Lisa",90)
   y: (Int, String, Int) = (1,Lisa,90)

• 元组的取值，角标从1开始

   scala> y._1
   res56: Int = 1
  
   scala> y._2
   res57: String = Lisa
  
   scala> y._3
   res58: Int = 90

3. 集合

Scala的集合有三大类：序列Seq、集Set、映射Map，所有的集合都扩展自Iterable特质

在Scala中集合有可变（mutable）和不可变（immutable）两种类型

3.1 序列

不可变：List

可变：ListBuffer