1、定义变量
var 可变
val 不可变,相当于Java中的final
Unit相当于Java中的void,以()表示
scala> val a = println("ddd") ddd a: Unit = ()
2,声明数组
scala> val arr = Array(1,2,3,4,5) arr: Array[Int] = Array(1, 2, 3, 4, 5)
3,for循环
scala> for(ele <- arr){ println(ele) } 1 2 3 4 5
scala> for(ele <- 0 to 4) { println(arr(ele)) } 1 2 3 4 5
scala> for(ele <- 0 until 5) { println(arr(ele)) } 1 2 3 4 5
带条件的循环
scala> for(ele <- arr if ele % 2==0) println(ele) 2 4
双层for循环
scala> for(i <- 1 to 3;j <- 1 to 3 if i !=j) println((10 * i j)) 12 13 21 23 31 32
把循环结果赋给一个新的数组
scala> val r1 = for(a <- arr if a % 2 == 0) yield a r1: Array[Int] = Array(2, 4)
4,定义方法
scala> def add(a: Int,b: Int) = a b add: (a: Int, b: Int)Int
scala> add(2,5) res7: Int = 7
无参无返回
scala> def say = println("hello") say: Unit
scala> say hello
方法转函数
scala> add _ res9: (Int, Int) => Int = <function2>
5,定义函数
scala> val fx = (a: Int,b: Int) => a b fx: (Int, Int) => Int = <function2>
scala> fx(3,6) res10: Int = 9
scala> val fn:(Int,Int) => Int = (x,y) => x y fn: (Int, Int) => Int = <function2>
scala> fn(6,2) res11: Int = 8
scala> val f1 = (name: String) => println(name) f1: String => Unit = <function1>
scala> f1("ggg") ggg
scala> val f2:(String) => Unit = name => println(name) f2: String => Unit = <function1>
scala> f2("hhh") hhh
6,传值调用(方法)和传名调用(函数)
传值是把100-5=95的值给循环了3次,输出3个95,传名是把countMoney方法隐式转换成函数,把函数整体传入循环,循环4次,money每次都会扣减5
代码语言：javascript复制object Money {
var money = 100
def payMoney = {
money -= 5
}
def countMoney = {
payMoney
money
}
def printByValue(x: Int) = {
for (a <- 0 until 3)
println(s"测试:${x}元")
}
def printByName(x: => Int) = {
for (a <- 0 to 3)
println(s"测试:${x}元")
}
def main(args: Array[String]): Unit = {
printByValue(countMoney)
printByName(countMoney)
}
}输出结果
测试:95元 测试:95元 测试:95元 测试:90元 测试:85元 测试:80元 测试:75元
代码语言：javascript复制object Calculate {
def add(a: Int,b: Int) = {
a b
}
def add2(f:(Int,Int) => Int,a: Int,b: Int) = {
f(a,b)
}
def add3(f:Int => Int,b: Int) = {
f(b) b
}
val fx = (a: Int,b: Int) => a b
val f = (a: Int) => a * 10
def main(args: Array[String]): Unit = {
println(add(6,1))
println(add2(fx,13,5))
println(add3(f,6))
}
}输出结果
7 18 66
7,可变参数以及参数的默认值
代码语言：javascript复制object ManyParams {
def add(ints: Int*) = {
var sum = 0
for (v <- ints) {
sum = v
}
sum
}
def dee(a: Int = 6,b: Int = 4) = {
a b
}
def main(args: Array[String]): Unit = {
val i = add(3,5)
println(i)
println(dee())
println(dee(b=1,a=6))
}
}输出结果
8 10 7
8,高阶函数
首先判断调用的layout方法是否满足apply的第一个函数参数,很明显,layout有一个Int的参数,返回的是字符串,完全符合f:Int => String,然后根据f(v),把v作用在f函数中.
代码语言：javascript复制object HightFunc extends App{
def apply(f:Int => String,v:Int) = f(v)
def layout(x:Int) = "[" x.toString "]"
println(apply(layout,10))
}输出结果
[10]
9,部分参数应用函数
scala> def m(a: Int,b: Int) = a b m: (a: Int, b: Int)Int
scala> val partM = m(1,_:Int) partM: Int => Int = <function1>
scala> partM(5) res14: Int = 6
scala> val partM2 = (x: Int) => m(1,x) partM2: Int => Int = <function1>
scala> partM2(6) res15: Int = 7
代码语言：javascript复制import java.util.Date
object PartParmFunc extends App{
def log(date: Date,message: String) = {
println(s"$date,$message")
}
val date = new Date()
val logBoundDate = log(date, _:String)
logBoundDate("gogogo")
}输出结果
Fri Sep 21 15:40:15 CST 2018,gogogo
10,柯里化
scala> def add(a: Int)(b: Int) = a b add: (a: Int)(b: Int)Int
scala> add(4)(8) res16: Int = 12
高阶函数演变
scala> def add(a: Int) = (b:Int) => a b add: (a: Int)Int => Int
scala> val x = add(5) x: Int => Int = <function1>
scala> x(8) res17: Int = 13
11,偏函数
代码语言：javascript复制object ScalaPartialFunction {
def func(str: String): Int = {
if (str.equals("a")) 97
else 0
}
/**
* 偏函数:PartialFunction[参数类型,返回值类型]
* @return
*/
def func1:PartialFunction[String,Int] = {
case "a" => 97
case _ => 0
}
def f1:PartialFunction[Any,Int] = {
case i:Int => i * 10
}
def main(args: Array[String]): Unit = {
println(func("a"))
println(func1("a"))
val arr = Array[Any](1,2,4,"你大爷的")
val arr1 = Array(1,3,6,8)
val collect = arr.collect(f1)
val collect1 = arr1.map((x: Int) => x * 10)
val collect2 = arr1.map(x => x * 10)
val collect3 = arr1.map(_ * 10)
val collect4 = arr1.map {case x: Int => x * 10}
println(collect.toBuffer)
println(collect1.toBuffer)
println(collect2.toBuffer)
println(collect3.toBuffer)
println(collect4.toBuffer)
}
}输出结果
97 97 ArrayBuffer(10, 20, 40) ArrayBuffer(10, 30, 60, 80) ArrayBuffer(10, 30, 60, 80) ArrayBuffer(10, 30, 60, 80) ArrayBuffer(10, 30, 60, 80)
12,数组使用
new关键字初始数组
scala> val arr = new Array[Int](3) arr: Array[Int] = Array(0, 0, 0)
scala> arr(0) = 100
scala> arr res1: Array[Int] = Array(100, 0, 0)
长度不可变,内容可变
map映射
代码语言：javascript复制val arr = Array(1,3,5,7,8)
//map映射
val fx = (x: Int) => x * 10
//ar1经过map映射操作后会返回一个新的数组
val ar1 = arr.map(fx)flatten,flatMap扁平化
scala> val arr = Array("hello tom","hello jenie") arr: Array[String] = Array(hello tom, hello jenie)
scala> arr.length res4: Int = 2
scala> arr.map(_.split(" ")) res5: Array[Array[String]] = Array(Array(hello, tom), Array(hello, jenie))
scala> arr.map(_.split(" ")).flatten res6: Array[String] = Array(hello, tom, hello, jenie)
scala> arr.flatMap(_.split(" ")) res7: Array[String] = Array(hello, tom, hello, jenie)
foreach遍历
scala> arr.flatMap(_.split(" ")).foreach(println) hello tom hello jenie
scala> arr.flatMap(_.split(" ")).foreach(x => println(x)) hello tom hello jenie
groupBy分组(Map)
scala> arr.flatMap(_.split(" ")).groupBy(x => x) res10: scala.collection.immutable.Map[String,Array[String]] = Map(jenie -> Array(jenie), tom -> Array(tom), hello -> Array(hello, hello))
Map取值(List)
scala> arr.flatMap(_.split(" ")).groupBy(x => x).map(x => x._2) res11: scala.collection.immutable.Iterable[Array[String]] = List(Array(jenie), Array(tom), Array(hello, hello))
取每个Map值的长度
scala> arr.flatMap(_.split(" ")).groupBy(x => x).mapValues(_.length) res12: scala.collection.immutable.Map[String,Int] = Map(jenie -> 1, tom -> 1, hello -> 2)
转成list(map不能排序)
scala> arr.flatMap(_.split(" ")).groupBy(x => x).mapValues(_.length).toList res13: List[(String, Int)] = List((jenie,1), (tom,1), (hello,2))
list排序(升序)
scala> arr.flatMap(_.split(" ")).groupBy(x => x).mapValues(_.length).toList.sortBy(x => x._2) res14: List[(String, Int)] = List((jenie,1), (tom,1), (hello,2))
list排序(降序)
scala> arr.flatMap(_.split(" ")).groupBy(x => x).mapValues(_.length).toList.sortBy(x => - x._2) res15: List[(String, Int)] = List((hello,2), (jenie,1), (tom,1))
13,集合使用
长度可变数组(ArrayBuffer)
scala> import scala.collection.mutable._ import scala.collection.mutable._
scala> val ab = ArrayBuffer(1,2,3) ab: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3)
scala> ab = (4,5,6) res17: ab.type = ArrayBuffer(1, 2, 3, 4, 5, 6)
scala> ab res18: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3, 4, 5, 6)
代码语言：javascript复制/**
* Array:
* 内容都可变
* 长度可变数组(ArrayBuffer)和长度不可变数组Array
*
* 在Scala中,集合分为可变集合(mutable)和不可变集合(immutable)
* 可变集合指的是:长度可变,内容可变
* 不可变集合:长度不可变,内容也不可变
*/不可变List
scala> val list = List(1,2,4) list: List[Int] = List(1, 2, 4)
scala> list = (5,7) <console>:13: error: value = is not a member of List[Int] list = (5,7) ^
scala> list(0) = 100 <console>:13: error: value update is not a member of List[Int] list(0) = 100
可变List(ListBuffer)
scala> import scala.collection.mutable.ListBuffer import scala.collection.mutable.ListBuffer
scala> val lb = ListBuffer(1,2,3,4) lb: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1, 2, 3, 4)
scala> lb = (8,9) res2: lb.type = ListBuffer(1, 2, 3, 4, 8, 9)
scala> lb res3: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1, 2, 3, 4, 8, 9)
scala> lb(0) = 100
scala> lb res5: scala.collection.mutable.ListBuffer[Int] = ListBuffer(100, 2, 3, 4, 8, 9)
不可变Map
scala> val mp = Map("xx" -> 1) mp: scala.collection.immutable.Map[String,Int] = Map(xx -> 1)
scala> mp res1: scala.collection.immutable.Map[String,Int] = Map(xx -> 1)
可变Map(HashMap)
scala> import scala.collection.mutable.HashMap import scala.collection.mutable.HashMap
scala> val hmp = HashMap("x" -> 1) hmp: scala.collection.mutable.HashMap[String,Int] = Map(x -> 1)
scala> hmp res0: scala.collection.mutable.HashMap[String,Int] = Map(x -> 1)
scala> hmp = "b" -> 0 res2: hmp.type = Map(b -> 0, x -> 1)
scala> hmp res3: scala.collection.mutable.HashMap[String,Int] = Map(b -> 0, x -> 1)
List方法
scala> Nil res5: scala.collection.immutable.Nil.type = List()
scala> val list = List(9,10,4,2,7,1) list: List[Int] = List(9, 10, 4, 2, 7, 1)
scala> list.head res6: Int = 9
scala> list.tail res7: List[Int] = List(10, 4, 2, 7, 1)
右结合::生成为新的List,所有结合前的不可变List不变
scala> 100 :: Nil res8: List[Int] = List(100)
scala> val l = Nil l: scala.collection.immutable.Nil.type = List()
scala> 9 :: l res9: List[Int] = List(9)
scala> l res10: scala.collection.immutable.Nil.type = List()
scala> 1::2::3::Nil res11: List[Int] = List(1, 2, 3)
scala> Nil.::(3) res0: List[Int] = List(3)
拼接生成新List
scala> val list = List(3,6,8) list: List[Int] = List(3, 6, 8)
scala> list res2: List[Int] = List(3, 6, 8)
scala> list List(7,0,1) res3: List[Int] = List(3, 6, 8, 7, 0, 1)
scala> list res4: List[Int] = List(3, 6, 8) //原list不变
头部合并( :, :)
scala> list. :(List(9)) res5: List[Int] = List(9, 3, 6, 8)
scala> list. :(9527) res6: List[Int] = List(9527, 3, 6, 8)
尾部合并(: )
scala> list : (1) res8: List[Int] = List(3, 6, 8, 1)
scala> list res9: List[Int] = List(3, 6, 8)
拼接2个List(:::)
scala> list ::: List(1,5,7) res10: List[Int] = List(3, 6, 8, 1, 5, 7)
统计条件数(count)
scala> list.count(x => x>2) res1: Int = 3
过滤(filter)
scala> list.filter(x => x>3) res2: List[Int] = List(6, 8)
排序(sorted,sortBy,sortWith)
scala> list.sorted res3: List[Int] = List(3, 6, 8)
scala> list.sortBy(x => x) res4: List[Int] = List(3, 6, 8)
scala> list.sortBy(x => - x) res5: List[Int] = List(8, 6, 3)
scala> val wds = List(("a",1),("c",4),("t",2)) wds: List[(String, Int)] = List((a,1), (c,4), (t,2))
scala> wds.sortBy(x => x._2) res6: List[(String, Int)] = List((a,1), (t,2), (c,4))
scala> wds.sortBy(x => - x._2) res7: List[(String, Int)] = List((c,4), (t,2), (a,1))
scala> wds.sortWith((x, y) => x._2 > y._2) res8: List[(String, Int)] = List((c,4), (t,2), (a,1))
分组(grouped)
scala> list.grouped(2).toList res9: List[List[Int]] = List(List(3, 6), List(8))
scala> list.grouped(1).toList res10: List[List[Int]] = List(List(3), List(6), List(8))
折叠(fold,foldLeft,foldRight)
scala> list.fold(0)((x, y) => x y) res11: Int = 17
scala> list.fold(0)(_ _) res13: Int = 17
scala> list.foldLeft(0)(_ - _) res14: Int = -17
scala> list.foldRight(0)(_ - _) res15: Int = 5
反转(reverse)
scala> list.reverse res17: List[Int] = List(8, 6, 3)
聚合(reduce,aggregate)
scala> list.reduce((x, y) => x y) res18: Int = 17
scala> list.aggregate(0)(_ _,_ _) res1: Int = 17
合并(union)
scala> val list2 = List(7,3,1) list2: List[Int] = List(7, 3, 1)
scala> list.union(list2) res2: List[Int] = List(3, 6, 8, 7, 3, 1)
交集(intersect)
scala> list.intersect(list2) res3: List[Int] = List(3)
区别(diff)
scala> list.diff(list2) res4: List[Int] = List(6, 8)
组合成元组(zip)
scala> list.zip(list2) res5: List[(Int, Int)] = List((3,7), (6,3), (8,1))
格式化字符串(mkString)
scala> list.mkString("|") res6: String = 3|6|8
scala> list.mkString("t") res7: String = 3 6 8
截取(slice)
scala> list.slice(1,3) res8: List[Int] = List(6, 8)
scala> list.slice(1,list.length) res10: List[Int] = List(6, 8)
求和(sum)
scala> list.sum res11: Int = 17
Set方法
不可变Set
scala> val set = Set(1,5,5,8) set: scala.collection.immutable.Set[Int] = Set(1, 5, 8)
可变Set(HashSet)
scala> import collection.mutable.HashSet import collection.mutable.HashSet
scala> val hset = HashSet(1,4,7) hset: scala.collection.mutable.HashSet[Int] = Set(1, 7, 4)
scala> hset.add(5) res12: Boolean = true
scala> hset res13: scala.collection.mutable.HashSet[Int] = Set(1, 5, 7, 4)
scala> hset.remove(1) res14: Boolean = true
scala> hset res15: scala.collection.mutable.HashSet[Int] = Set(5, 7, 4)
scala> hset.-=(5) res9: hset.type = Set(7, 4)
scala> hset Set(0,8) res10: scala.collection.mutable.HashSet[Int] = Set(0, 7, 4, 8)
scala> hset res11: scala.collection.mutable.HashSet[Int] = Set(7, 4) 此时原来的hset是无变化的
scala> hset = Set(0,8) res12: hset.type = Set(0, 7, 4, 8)
scala> hset res13: scala.collection.mutable.HashSet[Int] = Set(0, 7, 4, 8) 此时原来的hset是有变化的
不可变Map
scala> val mp = Map[String, Int]("a" -> 1) mp: scala.collection.immutable.Map[String,Int] = Map(a -> 1)
可变Map
scala> import collection.mutable.HashMap import collection.mutable.HashMap
scala> val mmp = HashMap[String, Int]() mmp: scala.collection.mutable.HashMap[String,Int] = Map()
scala> mmp.put("bb",8) res0: Option[Int] = None
scala> mmp res1: scala.collection.mutable.HashMap[String,Int] = Map(bb -> 8)
scala> mmp = "name" -> 100 res2: mmp.type = Map(bb -> 8, name -> 100)
添加元组
scala> mmp = (("xx",98)) res3: mmp.type = Map(bb -> 8, name -> 100, xx -> 98)
删除Key
scala> mmp.remove("xx") res4: Option[Int] = Some(98)
scala> mmp res5: scala.collection.mutable.HashMap[String,Int] = Map(bb -> 8, name -> 100)
scala> mmp.-=("name") res6: mmp.type = Map(bb -> 8)
通过Key获取value
scala> mmp.get("bb") res8: Option[Int] = Some(8)
scala> mmp.get("bb").get res9: Int = 8
如果没有Key，get就获取不到值
scala> mmp.get("aa") res10: Option[Int] = None
scala> mmp.get("aa").get java.util.NoSuchElementException: None.get at scala.None$.get(Option.scala:347) at scala.None$.get(Option.scala:345) ... 32 elided
通过getOrElse可以在没有Key的情况下，获取一个默认值，map本身不变；如果Key存在，则直接返回value.
scala> mmp.getOrElse("aa",0) res12: Int = 0
scala> mmp res13: scala.collection.mutable.HashMap[String,Int] = Map(bb -> 8)
scala> mmp.getOrElse("bb",0) res14: Int = 8
其中Some是一个样例类
代码语言：javascript复制package scala
@scala.SerialVersionUID(value = 1234815782226070388)
final case class Some[ A](val x : A) extends scala.Option[A] with scala.Product with scala.Serializable {
def isEmpty : scala.Boolean = { /* compiled code */ } //这里是false
def get : A = { /* compiled code */ } //这里就是x
}他有一个get方法
scala> Some(100) res15: Some[Int] = Some(100)
scala> Some(100).get res16: Int = 100
元组（元组中无论有多少个值，他在函数式编程中都是一个变量）
scala> val tuple = (1,true,"xx",Unit) tuple: (Int, Boolean, String, Unit.type) = (1,true,xx,object scala.Unit)
scala> tuple._3 res17: String = xx
scala> tuple._2 res18: Boolean = true
scala> tuple._4 res19: Unit.type = object scala.Unit
元组迭代器
scala> tuple.productIterator res20: Iterator[Any] = non-empty iterator
scala> tuple.productIterator.toList res21: List[Any] = List(1, true, xx, object scala.Unit)
scala> tuple.productIterator.foreach(println) 1 true xx object scala.Unit
对偶元组
scala> val tp1 = ("word", 4) tp1: (String, Int) = (word,4)
scala> tp1.swap //交换元素 res30: (Int, String) = (4,word)
