集合在程序中是非常有用的，只有用好集合才能真正感受到該語(yǔ)言的魅力。在scala中集合主要在三個(gè)包里面：scala.collection婴梧， scala.collection.immutable和scala.collection.mutable。
scala中引入不可變集合是為了方便程序的使用并減少在程序中的未知風(fēng)險(xiǎn)。如果一個(gè)集合被定義為不可變的胰舆，那么我們?cè)谑褂玫倪^(guò)程中就可以指定該集合是不會(huì)變化的，可以放心使用蹬挤。
我們看下這三個(gè)包的層次結(jié)構(gòu)：
scala.collection的層次結(jié)構(gòu)如下：
image.png
scala.collection.immutable的層次結(jié)構(gòu)如下：
image.png
scala.collection.mutable的層次結(jié)構(gòu)如下：
image.png
接下來(lái)我們通過(guò)兩個(gè)HashMap的例子來(lái)看一下immutable和mutable的使用缚窿。
mutable HashMap
我們看下怎么定義一個(gè)mutable hashMap :
import scala.collection.mutable.HashMap
println("\nStep 1: How to initialize a HashMap with 3 elements")
val hashMap1: HashMap[String, String] = HashMap(("PD","Plain Donut"),("SD","Strawberry Donut"),("CD","Chocolate Donut"))
println(s"Elements of hashMap1 = $hashMap1")
println("\nStep 2: How to initialize HashMap using key -> value notation")
val hashMap2: HashMap[String, String] = HashMap("VD"-> "Vanilla Donut", "GD" -> "Glazed Donut")
println(s"Elements of hashMap2 = $hashMap2")
怎么取出HashMap中的值：
println("\nStep 3: How to access elements of HashMap by specific key")
println(s"Element by key VD = ${hashMap2("VD")}")
println(s"Element by key GD = ${hashMap2("GD")}")
怎么改變hashMap：
println("\nStep 4: How to add elements to HashMap using +=")
hashMap1 += ("KD" -> "Krispy Kreme Donut")
println(s"Element in hashMap1 = $hashMap1")
println("\nStep 5: How to add elements from a HashMap to an existing HashMap using ++=")
hashMap1 ++= hashMap2
println(s"Elements in hashMap1 = $hashMap1")
println("\nStep 6: How to remove key and its value from HashMap using -=")
hashMap1 -= "CD"
println(s"HashMap without the key CD and its value = $hashMap1")
怎么定義一個(gè)空的HashMap：
println("\nStep 7: How to initialize an empty HashMap")
val emptyMap: HashMap[String,String] = HashMap.empty[String,String]
println(s"Empty HashMap = $emptyMap")
immutable HashMap
看一下怎么定義一個(gè)immutable HashMap：
import scala.collection.immutable.HashMap
println("Step 1: How to initialize a HashMap with 3 elements using Tuples of key and value")
val hashMap1: HashMap[String, String] = HashMap(("PD","Plain Donut"),("SD","Strawberry Donut"),("CD","Chocolate Donut"))
println(s"Elements of hashMap1 = $hashMap1")
println("\nStep 2: How to initialize HashMap using key -> value notation")
val hashMap2: HashMap[String, String] = HashMap("VD"-> "Vanilla Donut", "GD" -> "Glazed Donut")
println(s"Elements of hashMap2 = $hashMap2")
獲取HashMap中的值：
println("\nStep 3: How to access elements in HashMap by specific key")
println(s"Element by key VD = ${hashMap2("VD")}")
println(s"Element by key GD = ${hashMap2("GD")}")
我們?cè)倏匆幌略趺磳?duì)集合進(jìn)行操作，注意因?yàn)槭莍mmutable HashMap所以所有的操作都會(huì)返回一個(gè)新的HashMap：
println("\nStep 4: How to add elements to HashMap using +")
val hashMap3: HashMap[String, String] = hashMap1 + ("KD" -> "Krispy Kreme Donut")
println(s"Element in hashMap3 = $hashMap3")
println("\nStep 5: How to add two HashMaps together using ++")
val hashMap4: Map[String, String] = hashMap1 ++ hashMap2
println(s"Elements in hashMap4 = $hashMap4")
println("\nStep 6: How to remove key and its value from HashMap using -")
val hashMap5: Map[String, String] = hashMap4 - ("CD")
println(s"HashMap without the key CD and its value = $hashMap5")
更多教程請(qǐng)參考 flydean的博客
