Scala 映射

1、定义

　　在Scala中，映射（map）是一系列键值对的集合。也就是说建立了键和值的对应关系。在映射中，所有的值都可以通过键来找到。

映射包括两种，不可变和可变两种，默认创建的都是不可变映射，如果要创建可变映射，需要导入scala.collection.mutable.Map包。

 

2、创建映射

a、不可变映射

scala> val university = Map("XMU" -> "Xiamen University", "THU" -> "Tsinghua University","PKU"->"Peking University")
university: scala.collection.immutable.Map[String,String] = Map(XMU -> Xiamen University, THU -> Tsinghua University, PKU -> Peking University)

scala> university
res9: scala.collection.immutable.Map[String,String] = Map(XMU -> Xiamen University, THU -> Tsinghua University, PKU -> Peking University)

scala> print(university)
Map(XMU -> Xiamen University, THU -> Tsinghua University, PKU -> Peking University)

//获取某个值，可以通过对应的键来获取
scala> print(university("XMU"))
Xiamen University

//判断映射中是否包含某个值
scala> val bh = if(university.contains("XMU"))  university("XMU")  else 0
bh: Any = Xiamen University

scala> print(bh)
Xiamen University

 

b、不变映射

不可变映射不能更新键值、不能增加键值。想要更新、增加就需要创建可变映射

scala> import scala.collection.mutable.Map
import scala.collection.mutable.Map

scala> val university2 = Map("XMU" -> "Xiamen University", "THU" -> "Tsinghua University","PKU"->"Peking University")
university2: scala.collection.mutable.Map[String,String] = Map(XMU -> Xiamen University, THU -> Tsinghua University, PKU -> Peking University)

scala>  //更新已有元素的值

scala> university2("XMU") = "Ximan University"

scala>  //添加新元素

scala> university2("FZU") = "Fuzhou University"

scala> //也可以使用+=操作来添加新的元素，如下：

scala> university2 += ("TJU"->"Tianjin University") 
res11: university2.type = Map(XMU -> Ximan University, THU -> Tsinghua University, FZU -> Fuzhou University, TJU -> Tianjin University, PKU -> Peking University)

scala> university2 += ("SDU"->"Shandong University","WHU"->"Wuhan University")
res12: university2.type = Map(XMU -> Ximan University, SDU -> Shandong University, WHU -> Wuhan University, THU -> Tsinghua University, FZU -> Fuzhou University, TJU -> Tianjin University, PKU -> Peking University)

scala> print(university2)
Map(XMU -> Ximan University, SDU -> Shandong University, WHU -> Wuhan University, THU -> Tsinghua University, FZU -> Fuzhou University, TJU -> Tianjin University, PKU -> Peking University)　　

 

3、遍历输出

//输出key ,value
scala> for ((k,v) <-university2) printf("Code is : %s and name is: %s\n",k,v)
Code is : XMU and name is: Ximan University
Code is : SDU and name is: Shandong University
Code is : WHU and name is: Wuhan University
Code is : THU and name is: Tsinghua University
Code is : FZU and name is: Fuzhou University
Code is : TJU and name is: Tianjin University
Code is : PKU and name is: Peking University

//只输出key
scala> for (k<-university2.keys) println(k)
XMU
THU
PKU

//只输出value
scala> for (v<-university2.values) println(v)
Xiamen University
Tsinghua University
Peking University