Scala语法细节04--double_happy

1.字符串插值

spark源码里有很多这个如果遇到object调用方法要放入字符串里面记得加上{}

object StringApp {

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

    val greeting = "Hello:Ruozedata...."
    println(greeting)

    val name = "若泽数据"
    val welcome = "Hello:" + name
    println(welcome)

    // String interpolation
    println(s"Hello:$name")        //这块

    val msg =
      """
        |这是一个多行字符串
        |hello
        |若泽数据
      """.stripMargin
    println(msg)

  }

List （有序可重复的）

集合里一定要记住不适用new 方式创建的集合都是调用object里的apply方法

1.长度不可变
2.长度可变

1.长度不可变

Nil是什么？ 不可变的  空的List
	scala> Nil
	res0: scala.collection.immutable.Nil.type = List()

head 和 tail    头是一个  尾是除了第一个剩下的
     scala> val l1 = List(1,2,3,4,5)
	l1: List[Int] = List(1, 2, 3, 4, 5)

	scala> l1.head
	res1: Int = 1

	scala> l1.tail
	tail   tails
	
	scala> l1.tail
	res2: List[Int] = List(2, 3, 4, 5)

结合上面头和尾 不适用List如何创建一个list呢？
	::  使用它    前面放头（可以这么理解） 后面放尾
	 
	 scala> val l2 = 1 :: Nil
	l2: List[Int] = List(1)

	scala> val l3 = 2 :: l2
	l3: List[Int] = List(2, 1)
	
	scala> val l4 = 1 :: 2 :: 3 :: l3
	l4: List[Int] = List(1, 2, 3, 2, 1)

2.长度可变

scala> val l1 = scala.collection.mutable.ListBuffer[Int]()
l1: scala.collection.mutable.ListBuffer[Int] = ListBuffer()

scala> l1 +=1
res3: l1.type = ListBuffer(1)

scala> l1 += 2
res4: l1.type = ListBuffer(1, 2)

scala> l1 += (3,4,5)
res5: l1.type = ListBuffer(1, 2, 3, 4, 5)

scala> l1 ++= List(6,7,6,8)
res6: l1.type = ListBuffer(1, 2, 3, 4, 5, 6, 7, 6, 8)

scala> l1 -=2
res7: l1.type = ListBuffer(1, 3, 4, 5, 6, 7, 6, 8)

scala> l1 -=4
res8: l1.type = ListBuffer(1, 3, 5, 6, 7, 6, 8)

scala> l1 -=(1,3,4)
res9: l1.type = ListBuffer(5, 6, 7, 6, 8)

scala> l1 --=List(5,6,7)
res10: l1.type = ListBuffer(6, 8)

scala> l1.toList()
<console>:13: error: not enough arguments for method apply: (n: Int)Int in trait LinearSeqOptimized.
Unspecified value parameter n.
       l1.toList()
                ^

scala> l1.toList
res12: List[Int] = List(6, 8)

递归实现求和 ：别的太low 哈  面试掉价
  //递归方法要求是一定有返回值的
    def sum(nums : Int*) : Int = {

      if(nums.length == 0) 0

      else nums.head + sum(nums.tail : _*)

    }

    println(sum(1,2,3,5,6))

zipwithIndex

是将结果加上index

scala> val names = List("cxk","oyll","ailics")
names: List[String] = List(cxk, oyll, ailics)

scala> val score = List(4,6,10)
score: List[Int] = List(4, 6, 10)

scala> val result: List[(Int, String)] = score.zip(names)
result: List[(Int, String)] = List((4,cxk), (6,oyll), (10,ailics))

scala> result.zip
zip   zipAll   zipWithIndex

scala> result.zipWithIndex
res13: List[((Int, String), Int)] = List(((4,cxk),0), ((6,oyll),1), ((10,ailics),2))

scala> result.zipWithIndex.zipWithIndex
res14: List[(((Int, String), Int), Int)] = List((((4,cxk),0),0), (((6,oyll),1),1), (((10,ailics),2),2))

那么要求取出上面结果的 蔡徐坤 怎么取呢？  最好是filter一下 这里是写死的 
	
scala> result.zipWithIndex.zipWithIndex
res14: List[(((Int, String), Int), Int)] = List((((4,cxk),0),0), (((6,oyll),1),1), (((10,ailics),2),2))

scala> res1
res1   res10   res12   res13   res14

scala> res14(0)._1._1._2
res15: String = cxk

Set（无序不可重复）可以去重

scala> val list = List(1,2,3,4,4,4,5)
list: List[Int] = List(1, 2, 3, 4, 4, 4, 5)

scala> val set = Set(1,2,3,4,4,4,5)
set: scala.collection.immutable.Set[Int] = Set(5, 1, 2, 3, 4)

Map(k-v)

1.值不可变
2.值可变

1.值不可变

scala> val mp = Map("sx"->24,"dou_hap"->18)
mp: scala.collection.immutable.Map[String,Int] = Map(sx -> 24, dou_hap -> 18)

scala> mp("sx")
res16: Int = 24

scala> mp("cangjk")
java.util.NoSuchElementException: key not found: cangjk
  at scala.collection.MapLike$class.default(MapLike.scala:228)
  at scala.collection.AbstractMap.default(Map.scala:59)
  at scala.collection.MapLike$class.apply(MapLike.scala:141)
  at scala.collection.AbstractMap.apply(Map.scala:59)
  ... 32 elided

scala> mp("sx")=20
<console>:13: error: value update is not a member of scala.collection.immutable.Map[String,Int]
       mp("sx")=20
       ^

2.值可变（工作中要用这种的）

scala> val m = scala.collection.mutable.Map("ruoze"->20,"jepson"-> 18)
m: scala.collection.mutable.Map[String,Int] = Map(ruoze -> 20, jepson -> 18)

scala> m("canglaoshi")=38

scala> m
res20: scala.collection.mutable.Map[String,Int] = Map(ruoze -> 20, jepson -> 18, canglaoshi -> 38)

scala> m("canglaoshi")=35

scala> m
res22: scala.collection.mutable.Map[String,Int] = Map(ruoze -> 20, jepson -> 18, canglaoshi -> 35)

优化娶不到的人 不让他报错  getOrElse
	scala> m
res22: scala.collection.mutable.Map[String,Int] = Map(ruoze -> 20, jepson -> 18, canglaoshi -> 35)

scala> m("longlaoshi")
java.util.NoSuchElementException: key not found: longlaoshi
  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

scala> m.getOrElse("longlaoshi",27)
res24: Int = 27

scala> m.getOrElse("canglaoshi",27)
res25: Int = 35

spark源码里有很多 getOrElse

scala> m
res26: scala.collection.mutable.Map[String,Int] = Map(ruoze -> 20, jepson -> 18, canglaoshi -> 35)

scala> m +=("longlaoshi"->27,"bolaoshi"->31)
res27: m.type = Map(longlaoshi -> 27, bolaoshi -> 31, ruoze -> 20, jepson -> 18, canglaoshi -> 35)

scala> m -="ruoze"
res28: m.type = Map(longlaoshi -> 27, bolaoshi -> 31, jepson -> 18, canglaoshi -> 35)

scala> m.contains("ruoze")
res29: Boolean = false

scala> m.contains("jepson")
res30: Boolean = true

遍历Map;
val map = scala.collection.mutable.Map("longlaoshi" -> 27, "bolaoshi" -> 31, "jepson" -> 18, "canglaoshi" -> 35)

    for((k,v) <- map) {

      println(k +"-->" + v)
    }

    println("---------------")
    for((k,_) <- map) {

      println(k +"-->" +map.getOrElse(k,-99))
    }

    println("---------------")

    for(k <- map.keySet) {
      println(k +"-->" + map.getOrElse(k,-99))
    }

    println("---------------")

    for(v <- map.values) {
      println(v)
    }

结果：
longlaoshi-->27
bolaoshi-->31
jepson-->18
canglaoshi-->35
---------------
longlaoshi-->27
bolaoshi-->31
jepson-->18
canglaoshi-->35
---------------
longlaoshi-->27
bolaoshi-->31
jepson-->18
canglaoshi-->35
---------------
27
31
18
35

这种map是不能排序的

能排序的 sortedMap , LinkedHashMap

scala> val m = Map(1->2)
m: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)

scala> m.get(1)
res31: Option[Int] = Some(2)

scala> m.get(2)
res32: Option[Int] = None

scala> m.get(1).get
res33: Int = 2

scala> m.get(2).get
java.util.NoSuchElementException: None.get
  at scala.None$.get(Option.scala:347)
  at scala.None$.get(Option.scala:345)
  ... 32 elided

scala> m.get(1).getOrElse("None")
res35: Any = 2

scala> m.get(2).getOrElse("None")
res36: Any = None