Scala--Map操作

1、定義Map

1.1、定義不可變的Map也就是immutable

scala> val m = Map("Tom" -> 55,"Jak" -> 56,"Jim" -> 66)
m: scala.collection.immutable.Map[String,Int] = Map(Tom -> 55, Jak -> 56, Jim -> 66)

//通過->符號定義

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scala> val m = Map(("Tom",23),("Jack",45),("Tinna",66))
m: scala.collection.immutable.Map[String,Int] = Map(Tom -> 23, Jack -> 45, Tinna -> 66)

//通過元組的方式定義

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1.2、定義可變的Mapmutable

scala> val m = scala.collection.mutable.Map("Tom" -> 55,"Jak" -> 56,"Jim" -> 66)
m: scala.collection.mutable.Map[String,Int] = Map(Jim -> 66, Tom -> 55, Jak -> 56)

//通過指定scala.collection.mutable.Map來定義可變的Map

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2、訪問Map的元素

scala> m
res0: scala.collection.mutable.Map[String,Int] = Map(Jim -> 66, Tom -> 55, Jak -> 56)

scala> m("Tom")
res1: Int = 55

scala> m("Toms")
java.util.NoSuchElementException: key not found: Toms
at scala.collection.MapLike$class.default(MapLike.scala:228)
at scala.collection.AbstractMap.default(Map.scala:59)
at scala.collection.mutable.HashMap.apply(HashMap.scala:65)
... 32 elided

//直接獲取Map的元素的value，但是一旦這個元素不存在不會報錯，會報錯

scala> m.get("Tom")
res2: Option[Int] = Some(55)

scala> m.get("Toms")
res6: Option[Int] = None

//通過get方法獲取元素的值，一旦這個元素不存在的話就會返回None

scala> m.getOrElse("Tom",-1)
res4: Int = 55

scala> m.getOrElse("Toms",-1)
res7: Int = -1

//getOrElse方法，如果元素存在的話就會返回值，如果元素不存在的話就會返回-1

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3、修改Map元素的值，必須是mutable的Map才能修改

scala> m
res8: scala.collection.mutable.Map[String,Int] = Map(Jim -> 66, Tom -> 55, Jak -> 56)

scala> m("Tom") = 65

scala> m
res10: scala.collection.mutable.Map[String,Int] = Map(Jim -> 66, Tom -> 65, Jak -> 56)

//通過直接修改的方式修改元素的值

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4、遍歷Map的各個元素

scala> for(s <- m)println(s)
(Jim,66)
(Tom,65)
(Jak,56)

//通過for循環訪問Map的各個元素的值

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scala> m.foreach(println)
(Jim,66)
(Tom,65)
(Jak,56)

//通過Map的foreach來訪問Map的各個元素的值

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5、mutable 是 可變的 ，val 是不可變的，兩者是否沖突？

兩者是不會沖突的