Scala 学习笔记之集合(1)

package com.citi.scala

object CollectionDemo {
  def main(args: Array[String]): Unit = {

    /**
     * List
     */
    println("--------------------------List-------------------------")
    val numbers = List[Int](11, 22, 33, 44, 55)
    val numbers1 = List(11, 22, 33, 44, 55)
    val colors = List[String]("red", "green", "blue")
    println(s"colors has ${colors.size}, $colors")
    //取第一个
    println(colors.head)
    //去掉第一个，取剩下的
    println(colors.tail)
    //取第二个
    println(colors(1))
    //遍历
    for (s <- colors) { println(s) }
    //高阶函数使用
    colors.foreach { (s: String) => println(s) }
    colors.foreach { s => println(s) }
    colors.foreach { println(_) }
    val elSize = colors.map((s: String) => s.size)
    println(elSize)
    println(numbers.reduce((a: Int, b: Int) => a + b))
    //初始化空List
    val ls: List[Int] = List[Int]()
    val lls: List[Int] = Nil
    println(ls == lls)
    //遍历
    var i = numbers
    while (!i.isEmpty) {
      println(i.head)
      i = i.tail
    }

    i = numbers
    while (i != Nil) {
      println(i.head)
      i = i.tail
    }
    //cons操作符
    val consNumbers = 3 :: 2 :: 1 :: Nil
    println(consNumbers)

    //List的算数运算
    println(3 :: 2 :: 1 :: Nil)
    println(List(7, 6, 5) ::: List(4, 3, 2, 1))
    println(List(4, 3, 2, 1) ++ List(7, 6, 5))
    println(List(1, 2) == List(2, 1))
    println(List(2, 1) == List(2, 1))
    println(List(1, 2, 3, 2, 1).distinct)
    println(List(1, 2, 3, 2, 1) drop (2))
    println(List(4, 3, 2, 1) filter { _ >= 3 })
    println(List(List(1, 2, 3), List(4, 5, 6)).flatten)

    println((List(1, 2, 3, 4, 5).partition(_ >= 3)))
    println(List(1, 2, 3, 4, 5) reverse)
    println(List(2, 3, 5, 7, 10, 11) slice (1, 4))
    println(List("apple", "ben") sortBy { s => s.size })
    println(List(2, 3, 5, 7, 10, 11) splitAt (3))
    println(List(2, 3, 5, 7, 10, 11) take (3))
    println(List(1, 2, 3) zip List("a", "b"))
    println(List(1, 2) :+ 3)

    /**
     * Set
     */
    println("--------------------------Set-------------------------")
    val numbersets = Set[Int](11, 22, 11, 33, 44, 55)
    println(s"numbersets has ${numbersets.size}, $numbersets")
    println(numbersets.reduce((a: Int, b: Int) => a + b))
    /**
     * Map
     */
    println("--------------------------Map-------------------------")
    val colorMap = Map[String, Int]("red" -> 1, "green" -> 2, "yellow" -> 3)
    println(colorMap("red"))
    for (pair <- colorMap) { println(pair) }

  }
}

运行结果：

--------------------------List-------------------------
colors has 3, List(red, green, blue)
red
List(green, blue)
green
red
green
blue
red
green
blue
red
green
blue
red
green
blue
List(3, 5, 4)
165
true
11
22
33
44
55
11
22
33
44
55
List(3, 2, 1)
List(3, 2, 1)
List(7, 6, 5, 4, 3, 2, 1)
List(4, 3, 2, 1, 7, 6, 5)
false
true
List(1, 2, 3)
List(3, 2, 1)
List(4, 3)
List(1, 2, 3, 4, 5, 6)
(List(3, 4, 5),List(1, 2))
List(5, 4, 3, 2, 1)
List(3, 5, 7)
List(ben, apple)
(List(2, 3, 5),List(7, 10, 11))
List(2, 3, 5)
List((1,a), (2,b))
List(1, 2, 3)
--------------------------Set-------------------------
numbersets has 5, Set(33, 22, 44, 11, 55)
165
--------------------------Map-------------------------
1
(red,1)
(green,2)
(yellow,3)