scala集合-List

参考：https://www.runoob.com/scala/scala-lists.html

　　　https://www.jianshu.com/p/24c0ed2e3ae8　

1. 默认scala的List是可不变的，值一旦被定义了就不能改变了，所以列表改变后都需要重新赋值。

2. ListBuffer（可变长集合）

 2020-04-22

1.导包
import scala.collection.mutable.ListBuffer

2. 声明
scala> val lb = ListBuffer(1,4)
lb: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1,4)

3.常用操作
增加元素
scala> lb += 5
res17: lb.type = ListBuffer(1, 4, 5)

scala> lb ++= List(10, 20)
res18: lb.type = ListBuffer(1, 4, 5, 10, 20)

scala> lb ++= Array('b', 'c')
res19: lb.type = ListBuffer(1, 4, 5, 10, 20, 98, 99)

按照下标插入几个元素
scala> lb.insert(0, 2 ,2, 3)
scala> lb
res21: scala.collection.mutable.ListBuffer[Int] = ListBuffer(2, 2, 3, 1, 4, 5, 10, 20, 98, 99)

按照值删除元素
scala> lb -= 99
res23: lb.type = ListBuffer(2, 2, 3, 1, 4, 5, 10, 20, 98)

scala> lb --= Array(2, 3, 1, 4)
res24: lb.type = ListBuffer(2,5, 10, 20, 98)

按照下标删除几个元素
scala> lb.remove(0, 2)
scala> lb
res26: scala.collection.mutable.ListBuffer[Int] = ListBuffer(10, 20, 98)

根据下标更新元素值
scala> lb(0) = 33
scala> lb
res28: scala.collection.mutable.ListBuffer[Int] = ListBuffer(33, 20, 98)

与Array转换
scala> lb.toArray
res27: Array[Int] = Array(10, 20, 98)