scala(集合)-第四天

1、数组
   定长数组
       val a = new Array[String](5)   //长度为五
       a.length   //5
       a(1)="hello"   //赋值

val b = Array("hadoop","spark") //底层调用的apply，在apply中调用new Array[]()

       val c = Array(1,2,3,4,5,6,7,8,9)
       c.mkString   //123456789
       c.mkString(",")   //1,2,3,4,5,6,7,8,9
       c.mkString("<",",",">")   //<1,2,3,4,5,6,7,8,9>
       c.toString   //[I@9e54c59
   变长数组
       val d = scala.collection.mutable.ArrayBuffer[Int]()
       d.length   //0
       d += 1
       d += 2
       d += (3,4,5)
       d ++= Array(6,7,8)
       d.insert(0,0)   //n:Int,eles:A*
       d.remove(1，1)   //n:Int,count:Int    从n开始删除count个元素
       d.trimEnd(2)   //删除后两个，从尾巴开始删

       println(d)   //ArrayBuffer(1,2)

       for(ele <- d){
           println(ele)
       }

       for(i <- 0 until c.length)

for(i <- (0 until c.length).reverse) //从后往前遍历

d.toArray //变成定长数组，从变长到鼎昌

2、List
Nil //scala.collection.immutable.Nil.type = List() 即Nil是空集合

   定长
       val l = List(1,2,3,4,5)   //一个List是油一个head和一个tail构成的
       l.head   //1
       l.tail   //List(2,3,4,5)

val l2 = 1 ::Nil //List(1)
val l3 = 2 :: l2 //List(2,1)

   可变
       val l5 = scala.collection.mutable.ListBuffer[Int]()
       l5 += 2
       l5 +=(3,4,5)
       l5 ++= List(6,7,8,9)

l5 -=2
l5 -=(1,3) //有就删，没有就不管，不会报错

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       l5.isEmpty
       l5.head   //与List相同
       l5.tail
       l5.tail.head

l5.toList
l5.toArray

       def sum(num:Int*):Int={
           if(nums.length == 0){
               0
           }else{
               nums.head + sum(nums.tail:_*)   //. :_*将Seq转变为可变参数
           }
       }

3、Set(无序，不重复)
不可变
val set = Set(1,2,2,1,4,3) //scala.collection.immutable.Set[Int] = Set(1,2,4,3)

可变
val set = scala.collection.mutable.Set[Int]()

//用法与list相同

4、Map
   不可变
       val a = Map("pk"->18,"messi"->20)
       a("pk")   //18
       a("pk")=19   //报错

   可变
       val b = scala.collection.mutable.Map("pk"->18,"messi"->20)
       b("pk")=19   //可以运行
       b.getOrElse("pk",9)   //有就取，没有就用9
       b.get("pk")   //Option[Int]=Some(18)
       b.get("pk").get    //18

       b("lisi")=40
       b += ("wangwu"->4,"zhaoliu"->5)
       b -= "wangwu"   //只需要指定key

val c = scala.collection.mutable.HashMap[String,Int]() //c:scala.collection.mutable.HashMap[String,Int]=Map()

       遍历
           for((key,value)<-b){
               println(key +":"+value)
           }

           for(key <- b.keySet){
               println(key + ":"+ b.getOrElse(key,9))
           }

           for(value <- b.values){
               println(value)
           }

           for((key,_)<-b){
               println(key +":"+b.getOrElse(key,9))
           }

5、Option&Some&None
   case object None extedns Option[Nothing]{
       def isEmpty = true
       def get = throw new NoSuchElementException("None.get")
   }

   final case class Some[+A](x: A) extends Option[A]{
       def isEmpty = false
       def get = x
   }

6、Tuple
元组
val a = (1,2,3,4,5)

a._1
a._2

   遍历
       for (i <- 0 until (a.productArity)){
           println(a.productElement(i))
       }

       val hostPort =("localhost",8080)
       hostPort._1
       hostPort._2

scala(集合)-第四天

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