Scala 基础语法（二）

定义变量

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val a=1
var b=1
val c="gec"
val d:Int=100
val e:Double=3.14
val f=3.14

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条件表达式

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val a=1
val b=if(a<0) -1 else 1
val b=if(a<0){
-1
}else{
1
}

val b=if(a<0)-1

val b=if(a<0) -1 else "gec"

val b=if(a<0) -1 else ()

val b=if(a<0) -1 else if(a==0) 0 else 1

val result={
val b=a+1
val c=b+1
val d=c+1
d
}

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循环

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1 to 10

for(i <- 3 to 10) println(i)

val range=1 to 10

for(i <- range) println(i)

for(i <- 1 to 3){
for(j <- 1 to 3){
println(i+" "+j)
}
}

for(i<- 1 to 3;j<- 1 to 3 if i!=j) println(i+j)

for(i <- 1 to 10) yield i*10

while(a>0){
println(a)
a=a-1
}

1+2
1.+(2)

def m1(x:Int,y:Int):Int=x+y

def m1(x:Int,y:Int)=x+y

m2(4)=4*3*2*1

://error
def m2(x:Int)={
if(x==1) 1
else x*m2(x-1)
}

def m2(x:Int):Int={
if(x==1) 1
else x*m2(x-1)
}

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声明函数

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(x:Int,y:Int) => x+y

val f1=(x:Int,y:Int)=>x+y
f1(1,2)

val f2=(x:Int,y:Int,z:Int)->x+y+z

def m1(x:Int,y:Int):Int=x+y
val f1=(x:Int,y:Int)=>x+y
val f2=m1 _
f2(1,2)

 def m1(x:Int,y:Int):Int=x+y

def m1(x:Int,y:Int)=x+y

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递归函数

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def m2(x:Int):Int={
if(x==1) 1
else x*m2(x-1)
}

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匿名函数

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(x:Int,y:Int)=>x+y

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定义函数

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val f1=(x:Int,y:Int)=>x+y

f1(1,2)

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定义函数

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val f2=(x:Int,y:Int,z:Int)=>x+y+z

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定义一个方法

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def m1(x:Int,y:Int):Int=x+y

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定义函数

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val f1=(x:Int,y:Int)=>x+y

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方法转换函数

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val f2=m1 _

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//定长数组

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val array=new Array[Int](5);
val array1=Array(1,2,3,4);

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获取数组元数

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array(0)

import scala.collection.mutable.ArrayBuffer
val array=ArrayBuffer[Int]()

array+=1
array+=(1,2,3,4,5,6,7,8,9,10)

array ++=Array(5,6)

//error
val a1=Array(1,2,3)
a1 +=4

array(0)=100
array -=100
array -(2,3,4)
array --Array(5)
array --ArrayBuffer(6,7)

for(i <- array) println(i)

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获取数组的下标

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0 until 5

0 until array.length

for(i <- 0 until array.length) println(array(i))
for(i <- (0 until array.length).reverse) println(array(i))
for(i <- array if i%2==0) println(i)
var array3=for(i <- array if i%2==0) yield i*10
array.filter

val f1=(x:Int)=>x%2==0
array.filter(f1)
array.filter((x:Int)=>x%2==0)
array.filter(x=>x%2==0)
array.filter(_ % 2==0)

for(int a:array)
{
if(a%2==0)
{
println
}
}

array.filter(_ % 2==0).map

val f2=(x:Int)=>x*10
array.filter(_ % 2 ==0).map(f2)
array.filter(_ % 2 ==0).map((x:Int)=>x*10)
array.filter(_ % 2 ==0).map(x=>x*10)
array.filter(_ % 2 ==0).map(_*10)

array.max
array.min
array.sum
array.sorted
Array(6,4,5,3,1,2).sorted
Array(6,4,5,3,1,2).sorted.reverse

val map=Map("zhangsan"->30,"lisi"->40)
val map1=Map(("zhangsan",30),("lisi",40))
map("zhangsan")
map1("lisi")
map1.getOrElse("wangwu",50)
map1.getOrElse("lisi",50)
map1.getOrElse("lisi00",50)
import scala.collection.mutable.HashMap

val hmap=HashMap("zhangsan"->30)
hmap +=("list"->40)
hmap +=("lisi"->50,"wangwu"->60)
hmap("lisi")=100
hmap -=("lisi")
hmap.remove("wanggu")

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映射key value

//map是不可变的类

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scala.collection.immutable.Map
val map=Map("zhangsan"->30)
val map=Map("zhangsan"->30,"lisi"->40)
val map=Map(("zhangsan",30),("lisi",40))
map("zhangsan")
map1("lisi")
map1.getOrElse("wangwu",50)

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//HashMap是可变的类

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import scala.collection.mutable.HashMap
var hmap=HashMap("zhangsan"->30)

hmap +=("lisi"->40)
hmap +=("lisi"->50,"wangwu"->60)

hmap -=("lisi")
hmap.remove("wangwu")

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//error

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map1+=("a"->50)
map1+=("a"->50)

val tuple=("hadoop",3.14,100)
tuple._1
tuple._2
tuple._3

var array=Array(("zhangsan",30,"football"),("lisi",40,"swimming"))
var array=Array(("zhangsan",30,"Beijing"),("lisi",40,"shanghai"))

array.toMap

val names=Array("zhangsan","lisi")
val ages=Array(30,40,50)
names.zip(ages)
val names=Array("zhangsan","lisi","wangwu")
names.zip(ages)
names.zipAll(ages,"zhaoliu",50)

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list特点:

存储有序的数据

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val list=List(1,2,3,4,5,6,7,8,9,10)
list.head

list.tail

List(1).head
List(1).tail

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//创建一个list集合，里面存储1个数据

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1::Nil

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//与1::Nil等效写法

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1::List()

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//创建一个list集合，里面存储3个数据，分别是1,2,3

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1::2::3::Nil

val list=List(1,2,3)

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在集合头部位置添加数据

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list.+:(4)
list.::(5)

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在集合尾部位置添加数据

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list.:+(4)

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在集合尾部位置添加多条数据

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list.++(List(4,5,6))

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在集合头部位置添加多条数据

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list.:::(List(4,5,6))

import scala.collection.mutable.ListBuffer
val list=ListBuffer(1)
list +=2
list +=3

list.append(4,5,6)

list ++=List(7,8)
list ++=ListBuffer(9,10)

list -=1
list -=2
list -=3
list --=List(4,5,6)
list --=ListBuffer(7,8)

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作业题

创建一个List

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val list0=List(1,7,9,8,0,3,5,4,6,2)

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如何遍历集合

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for(i <- list0) yield i*10

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作用：实现集合的二次赋值

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list0.map((x:Int)=>x*10)
//将list0中的每一个元素乘以10后生成一个新的集合
list0.map(x=>x*10)
list0.map(_*10)
list0.map(x=>x+"gec")
//将list0中的每一个元素乘以10后生成一个新的集合
list0.Filter(x=>x%2==0)
list0.Filter(_%2==0)

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//正向排序

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list0.sorted

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//反向排序

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list0.sorted.reverse

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//二次排序逻辑处理实现

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list0.sortBy(x=>x)
list0.sortBy(x=>x).reverse
list0.sortWith((x:Int,y:Int)=>x<y)

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//将List0中的元素4个一组，类型Iterator[List[Int]]

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list0.grouped(4)

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//将Iterator转换成List

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list0.grouped(4).toList

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//将多个list压扁成一个List

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list0.grouped(4).toList.flatten

val lines=List("hello tom hello jerry","hello jerry","hello kitty")

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//先按空格切分，再压平

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lines.map(x=>x.split(" "))
lines.map(x=>x.split(" ")).flatten
lines.flatMap(x=>x.split(" "))
lines.flatMap(_.split(" "))

list0.sum
list0.max
list0.min

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//并行计算求和

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list0.par.sum

def reduce[A1 >: Int](op: (A1, A1) => A1): A1
list0.reduce

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//将非特定顺序的二元操作应用到所有元素

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list0.reduce((x:Int,y:Int)=>x+y)
list0.reduceLeft(((x:int,y:int)=>x+y)
list0.reduceRight(((x:int,y:int)=>x+y)
list0.reduce(_+_)
list0.reduce(_-_)
list0.reduceLeft(_-_)
list0.reduceRight(_-_)

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//折叠

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list0.fold
list0.fold(0)((x:Int,y:Int)=>x+y)
list0.fold(10)((x:Int,y:Int)=>x+y)
list0.foldLeft(10)((x:Int,y:Int)=>x+y)
list0.foldRight(10)((x:Int,y:Int)=>x+y)

res23: List[Int] = List(1, 7, 9, 8, 0, 3, 5, 4, 6, 2)
def fold[A1 >: Int](z: A1)(op: (A1, A1) => A1): A1

list0.fold(10)((x,y)=>{println("x="+x+" y="+y);1;})
list0.fold(10)(_+_)

val list10=List(List(1,2,3),List(4,5,6),List(7,8),List(9,0))

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//聚合

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list10.par.aggregate
def aggregate[S](z: => S)(seqop: (S, List[Int]) => S,combop: (S, S) => S): S

list10.par.aggregate(10)()

list10.par.aggregate(10)(_+_.sum,_+_)

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拆分开：

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list10.aggregate(0)(
(acc, number) => {
val res1 = acc + number.sum
println("par " + acc + " + " + number+" = "+res1)
res1
},
(par1, par2) => {
val res2 = par1 + par2
println("com " + par1 + " + " + par2+" = "+res2)
res2
}
)

 

println(list10.par.collect{
case _=>Thread.currentThread().getName
}.distinct)

val list=List(1,2,3,4)
val list1=List(1,2,3,4)
val list2=List(3,4,5,6)
list1.union(list2)
list1.intersect(list2)
list1.diff(list2)
list2.diff(list1)

val list10=List(List(1,2,3),List(4,5,6),List(7,8),List(9,0))

list10.aggregate(0)(
(acc, number) => {
val res1 = acc + number
println("par " + acc + " + " + number+" = "+res1)
res1
},
(par1, par2) => {
val res2 = par1 + par2
println("com " + par1 + " + " + par2+" = "+res2)
res2
}
)

 

val set=Set(1,2,3,4)
set.size
set.max
set.min

set & Set(3,4,5,6)

set ++ Set(3,4,5,6)

set --Set(3,4,5,6)

val map=Map("zhangsan"->30,"lisi"->40)
map.keys
map.keySet

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四种遍历方式

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for(k<-map.keys)println(k+"-> "+map(k))
for(k<-map.keySet)println(k+"-> "+map(k))
for((k,v)<-map) println(k+" > "+v)
map.foreach{case(x,y)=>println(x+"->"+y)}

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