Scala 基础语法（二）
定义变量
val a=1
var b=1
val c="gec"
val d:Int=100
val e:Double=3.14
val f=3.14
条件表达式
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
}
循环
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)
}
声明函数
(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
递归函数
def m2(x:Int):Int={
if(x==1) 1
else x*m2(x-1)
}
匿名函数
(x:Int,y:Int)=>x+y
定义函数
val f1=(x:Int,y:Int)=>x+y
f1(1,2)
定义函数
val f2=(x:Int,y:Int,z:Int)=>x+y+z
定义一个方法
def m1(x:Int,y:Int):Int=x+y
定义函数
val f1=(x:Int,y:Int)=>x+y
方法转换函数
val f2=m1 _
//定长数组
val array=new Array[Int](5);
val array1=Array(1,2,3,4);
获取数组元数
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)
获取数组的下标
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")
映射key value
//map是不可变的类
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)
//HashMap是可变的类
import scala.collection.mutable.HashMap
var hmap=HashMap("zhangsan"->30)
hmap +=("lisi"->40)
hmap +=("lisi"->50,"wangwu"->60)
hmap -=("lisi")
hmap.remove("wangwu")
//error
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)
list特点:
存储有序的数据
val list=List(1,2,3,4,5,6,7,8,9,10)
list.head
list.tail
List(1).head
List(1).tail
//创建一个list集合，里面存储1个数据
1::Nil
//与1::Nil等效写法
1::List()
//创建一个list集合，里面存储3个数据，分别是1,2,3
1::2::3::Nil
val list=List(1,2,3)
在集合头部位置添加数据
list.+:(4)
list.::(5)
在集合尾部位置添加数据
list.:+(4)
在集合尾部位置添加多条数据
list.++(List(4,5,6))
在集合头部位置添加多条数据
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)
作业题
创建一个List
val list0=List(1,7,9,8,0,3,5,4,6,2)
如何遍历集合
for(i <- list0) yield i*10
作用：实现集合的二次赋值
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)
//正向排序
list0.sorted
//反向排序
list0.sorted.reverse
//二次排序逻辑处理实现
list0.sortBy(x=>x)
list0.sortBy(x=>x).reverse
list0.sortWith((x:Int,y:Int)=>x<y)
//将List0中的元素4个一组，类型Iterator[List[Int]]
list0.grouped(4)
//将Iterator转换成List
list0.grouped(4).toList
//将多个list压扁成一个List
list0.grouped(4).toList.flatten
val lines=List("hello tom hello jerry","hello jerry","hello kitty")
//先按空格切分，再压平
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
//并行计算求和
list0.par.sum
def reduce[A1 >: Int](op: (A1, A1) => A1): A1
list0.reduce
//将非特定顺序的二元操作应用到所有元素
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(_-_)
//折叠
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))
//聚合
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,_+_)
拆分开：
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
四种遍历方式
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)}
