scala学习二：scala进阶

scala学习二：scala进阶

标签（空格分隔）： scala

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一，函数的求值策略

call by value
call by name(=>)

def test1(x:Int,y:Int):Int=x+x                  //> test1: (x: Int, y: Int)Int

def test2(x: => Int,y: => Int):Int=x+x          //> test2: (x: => Int, y: => Int)Int

test1(3+4,8)                                    //> res0: Int = 14
test2(3+4,8)                                    //> res1: Int = 14

二，scala的函数参数

1，默认参数

def func1(name:String="tom")="hello "+name      //> func1: (name: String)String
func1()                                         //> res0: String = hello tom
func1("marray")                                 //> res1: String = hello marray

2，带名参数

def func2(name:String="tom",age:Int=20)={
name+" age is "+age
}                                               //> func2: (name: String, age: Int)String

func2()                                         //> res2: String = tom age is 20
func2(age=25)                                   //> res3: String = tom age is 25

3，变长参数(*)

def sum(args:Int*)={
  var result=0
  for(arg <- args)
    result+=arg

  result
}                                               //> sum: (args: Int*)Int

sum(1,2,3)                                      //> res4: Int = 6

三,scala的Lazy值

当val被申明为lazy时，它的初始化被推迟，直到我们首次使用它。

val words="hello world"                         //> words  : String = hello world
lazy val words2="hello world"                   //> words2: => String
words2                                          //> res0: String = hello world

四,scala的异常处理

throw new Exception("some error happened")

//> java.lang.Exception: some error happened
//|     at demo5$$anonfun$main$1.apply$mcV$sp(demo5.scala:10)
//| 	at org.scalaide.worksheet.runtime.library.WorksheetSupport$$anonfun$$exe
//| cute$1.apply$mcV$sp(WorksheetSupport.scala:76)
//|     at org.scalaide.worksheet.runtime.library.WorksheetSupport$.redirected(W
//| orksheetSupport.scala:65)
//|     at org.scalaide.worksheet.runtime.library.WorksheetSupport$.$execute(Wor
//| ksheetSupport.scala:75)
//|     at demo5$.main(demo5.scala:1)
//|     at demo5.main(demo5.scala)

try{
  var words=scala.io.Source.fromFile("d:\\temp\\a.txt").mkString
}catch{
  case ex:java.io.FileNotFoundException => {
    println("========error block===================================")
  }
}finally{
  println("========finally block===================================")
}                                       
//> ========error block===================================
//| ========finally block===================================

五，数组类型

定长数组(Array)

val a=new Array[Int](10)
val b=new Array[String](10)
val c=Array("tom","mike","mary")

变长数组（ArrayBuffer）

val d=ArrayBuffer[Int]()
d += 1
d += 2
d += (10,11,12)
//去掉最后2个值
d.trimEnd(2)

//convert to Array
d.toArray

数组的遍历

val c=Array("tom","mike","mary")
//使用for循环遍历
for(s <- c) println(s)

//对数组进行转换，新生成一个数组
val n=for{
    s <- c
    s1=s.toUpperCase
}yield(s1)

数组的常用操作：

val myArray=Array(1,10,2,3,5,4)           //> myArray  : Array[Int] = Array(1, 10, 2, 3, 5, 4)
//max
myArray.max                               //> res0: Int = 10
//min
myArray.min                               //> res1: Int = 1
//sum
myArray.sum                               //> res2: Int = 25

val myArray=ArrayBuffer(1,10,2,3,5,4)
//sort desc
myArray.sortWith(_>_)
//asc
myArray.sortWith(_<_)

多维数组：

val myArray=Array.ofDim[Int](3,4)
//Array[Array[Int]] = Array(Array(0, 0, 0, 0), Array(0, 0, 0, 0), Array(0, 0, 0, 0))

myArray(1)(2)=10
//Array[Array[Int]] = Array(Array(0, 0, 0, 0), Array(0, 0, 10, 0), Array(0, 0, 0, 0))

val triangle=new Array[Array[Int]](10)
for(i <- 0 until triangle.length){
  triangle(i)=new Array[Int](i+1)
}
triangle

res1: Array[Array[Int]] = Array(Array(0), Array(0, 0), Array(0, 0, 0), Array(0, 0, 0, 0), Array(0, 0, 0, 0, 0), Array(0, 0, 0, 0, 0, 0), Array(0, 0, 0, 0, 0, 0, 0), Array(0, 0, 0, 0, 0, 0, 0, 0), Array(0, 0, 0, 0, 0, 0, 0, 0, 0), Array(0, 0, 0, 0, 0, 0, 0, 0, 0, 0))

scala数组和java集合的转换

import scala.collection.mutable.ArrayBuffer
import scala.collection.JavaConversions.bufferAsJavaList
object demo5 {

    val buffer1 = ArrayBuffer("tom","mike","mary")
                                                  //> buffer1  : scala.collection.mutable.ArrayBuffer[String] = ArrayBuffer(tom, m
                                                  //| ike, mary)

    val pb=new ProcessBuilder(buffer1)        //> pb  : ProcessBuilder = java.lang.ProcessBuilder@4ada629a
    pb.command()                              //> res0: java.util.List[String] = [tom, mike, mary]

}

六，scala的Map和Tuple

import scala.collection.mutable.ArrayBuffer
import scala.collection.JavaConversions.bufferAsJavaList
object demo5 {

    //不可变的map
    val math=scala.collection.immutable.Map("alice" -> 80,"bob" -> 95,"mary" -> 70)
                                                  //> math  : scala.collection.immutable.Map[String,Int] = Map(alice -> 80, bob ->
                                                  //|  95, mary -> 70)
    //可变的map
    val english=scala.collection.mutable.Map("alice" -> 80,"bob" -> 95,"mary" -> 70)
                                                  //> english  : scala.collection.mutable.Map[String,Int] = Map(alice -> 80, bob -
                                                  //| > 95, mary -> 70)
  val chinese=scala.collection.mutable.Map(("alice",80),("bob",95),("mary",70))
                                                  //> chinese  : scala.collection.mutable.Map[String,Int] = Map(alice -> 80, bob -
                                                  //| > 95, mary -> 70)
}

//获取map的值
if(chinese.contains("alice")){
  chinese("alice")
}else{
  -1
}   

//简写
chinese.getOrElse("bob",-1)

//更新map的值
chinese("bob") =100
//添加新的元素
chinese +="tom" ->56                            //> res2: demo5.chinese.type = Map(alice -> 80, bob -> 100, tom -> 56, mary -> 7
                                              //| 0)
//删除元素
chinese -="tom"                                 //> res3: demo5.chinese.type = Map(alice -> 80, bob -> 100, mary -> 70)

迭代获取map的值：

for(s <- chinese) println(s)

tuple:不同类型值得集合

import scala.collection.mutable.ArrayBuffer
import scala.collection.JavaConversions.bufferAsJavaList
object demo5 {

    val t1 =(1,2,"tom")                       //> t1  : (Int, Int, String) = (1,2,tom)

    val t2=new Tuple2("mary",2)               //> t2  : (String, Int) = (mary,2)
    t2._1                                     //> res0: String = mary
    t2._2                                     //> res1: Int = 2

    t2.productIterator.foreach(println)       //> mary
                                                  //| 2

}