scala学习记录二

模式匹配

• Java：对一个值对象条件判断，返回针对不同的条件进行不同的处理
• scala:

  变量 match{
    case value1 => 代码1
    case value2 => 代码2
    case _ => 代码N
  

简单的switch case

object MatchApp  extends  App{
  val names = Array("Akiho Yoshizawa","YuiHatang","Aoi Sola");
  val name = names(Random.nextInt(names.length)); // 随机选

  name match {
    case "Akiho Yoshizawa" => println("吉老师。。。。")
    case "YuiHatang" => println("波老师。。。")
    case _ => println("不知道你们在说什么")
  }

  def judgeGrade(grade:String):Unit={
    grade match {
      case "A" => println("很好...")
      case "B" => println("还可以。。。")
      case "C" => println("一般。。。")
      case _ => println("需要努力。。。")
    }
  }

  judgeGrade("A")
  judgeGrade("B")
  judgeGrade("D")
}

双重过滤

def judgeGrade(grade:String,name:String):Unit={
  grade match {
    case "A" => println("很好...")
    case "B" => println("还可以。。。")
    case "C" => println("一般。。。")
    case _  if(name == "lisi") => println(name + "你是一个good boy 不过 需要努力。。。")
    case _  => println("需要努力。。。")
  }
}
judgeGrade("D","zhangsan")
judgeGrade("A","lisi")
judgeGrade("D","lisi")

数组过滤

def greeting(array:Array[String])={
  array match {
    case Array("zhangsan") => println("Hi: zhangsan"); // 如果数组中有张三
    case Array(x,y) => println("Hi: "+ x + " , "+y); // 打印含有两个元素的数组
    case Array("zhangsan",_*) => println("Hi: zhangsan and other friend" ) // zhangsan开头的数组元素
    case _ => println("Hi: everybody...")
  }
}
greeting(Array("zhangsan")) //Hi: zhangsan
greeting(Array("lisi","wangwu","zhaoyun")) //Hi: everybody...
greeting(Array("zhangsan","lisi","wangwu")) // Hi: zhangsan and other friend

List过滤

 def greeting(list:List[String])={
 list match {
    case "zhangsan" ::Nil => println("Hi:zhangsan");
    case x::y::Nil => println("Hi: "+ x + ", "+y);  //只有两个元素
    case "zhangsan"::tail => println("Hi zhangsan and other firends..") // 头加尾
    case _ => println("HI: everybody...")
 }
}
greeting(List("zhangsan")); //Hi:zhangsan
greeting(List("lisi","zhangsan")); // Hi: lisi, zhangsan
greeting(List("zhangsan","lisi")) // Hi: zhangsan, lisi
greeting(List("zhangsan","lisi","aa")) // Hi zhangsan and other firends..

类型匹配

def matchType(obj:Any)={
  obj match {
    case x:Int => println("Int");
    case x:String => println("String");
    case x:Map[_,_] => x.foreach(println);
    case _ => println("other type")
  }
}
matchType(1); //Int
matchType("1") // String
matchType(1f) // other type
matchType(Map("name"->"PK")) //(name,PK)

异常处理

object ExceptionApp extends  App {
  try {
    val i = 10/0;
  }catch {
    case e:ArithmeticException => println("除数不能为0。。。")
    case e: Exception => println(e.getMessage)
  }
  finally {
    //释放资源
  }

case class模式匹配

def caseclassMatch(person: Person)={
  person match {
    case CTO(name,floor)=>println("Cto name is: "+name+" , floor is "+floor)
    case Employee(name,floor)=>println("Employee name is: "+name+" , floor is "+floor)
    case _ => println("other")
  }
}
class Person;
case class  CTO(name:String,floor:String) extends Person;
case class  Employee(name:String,floor:String) extends Person;
case class  Other(name:String) extends Person;

caseclassMatch(CTO("PK","12 "))
caseclassMatch(Employee("zhangsan","2 "))
caseclassMatch(Other("other"))

scala函数高级

字符串高级操作

val s = "Hello:PK"
val name = "PK"
println(s+name)
println(s"Hello:$name")

var team = "AC Milan"
// 插值
println(s"Hello:$name,Welcome to $team") 

//多行字符串
val b =
  """
    |这是一个多行字符串
    |hello
    |world
    |PK
    |""".stripMargin
println(b)

匿名函数

def sayHello(name:String)={
  println(s"hi: $name")
}
sayHello("PK") //hi: PK
val sayHello2 = (name:String)=>println(s"Hi: $name")
sayHello2("zhangsan") //Hi: zhangsan

函数柯里化（curring）

def sum(a:Int,b:Int) = a+b
println(sum(2,3 ))

def sum2(a:Int)(b:Int)=a+b
println(sum2(2)(3))

高阶函数

  val l= List(1,2,3,4,5)
  //map：逐个去操作集合中的每个元素
//  val l2 = l.map((x:Int)=>x+1) // 每个元素加一
  val l2 = l.map(x=>x+1) // 参数为一个元素，括号可省略
  val l3 = l.map(_ + 1) // 占位符表示任意一个元素，既每个元素加一
  println(l2) //List(2, 3, 4, 5, 6)
  println(l3) //List(2, 3, 4, 5, 6)

  val l4 = l.map(_ + 1).filter(_ > 5) // 加一后，取出大于5的元素
  println(l4) //List(6)

  val l5 = l.take(2) // 取前两个元素
  println(l5) //  List(1, 2)
  // 1+2 3+3 6 + 4
  val l6 = l.reduce(_+_) // 相邻求和
  println(s"reduce $l6") //reduce 15

  //reduceLeft = ((((1-2)-3)-4)-5) 其实调用的flodLeft
  val l7 = l.reduceLeft(_-_)
  println(s"reduceLeft $l7") // reduceLeft -13
  //reduceRight = (1-(2-(3-(4-5)))) 其实调用的flodRight
  val l8 = l.reduceRight(_-_)
  println(s"reduceRight $l8") // reduceRight 3

  // fold 计算公式为 0 - 1 -2 -3 - 4 - 5
  val l9 = l.fold(0)(_-_)
  println(s"fold $l9") // fold -15

  val l10 = l.foldLeft(0)(_-_)
  println(s"foldLeft $l10") //foldLeft -15

  val f = List(List(1,2),List(3,4),List(5,6))
  println(f.flatten)  // 展平 List(1, 2, 3, 4, 5, 6)

  // flatMap
  println(f.map(_.map(_*2)))  // List(List(2, 4), List(6, 8), List(10, 12))
  println(f.flatMap(_.map(_*2))) // List(2, 4, 6, 8, 10, 12)

  val text = scala.io.Source.fromFile(path+"\\hello.txt").mkString
  println(text) //hello,world,hello,hello

  val texts = List(text)
  var texts1 = texts.flatMap(_.split(",")).map(x=>(x,1))
  println("groupBy: "+texts1.groupBy((_._1))) 
  //groupBy: Map(world -> List((world,1)), hello -> List((hello,1), (hello,1), (hello,1)))

  println("Key: "+ texts1.map(_._1)) //_1 相当于key
  // Key: List(hello, world, hello, hello)

  println("Value: "+ texts1.map(_._2)) //_2 相当于value
  Value: List(1, 1, 1, 1)
  
  // groupBy 按key分组
  //第一个占位符表示含有(key,1)的list，经过groupBy后分为不同的(key1,value),(key2,value)
  

  println(texts1.groupBy(_._1).mapValues(_.foldLeft(0)(_+_._2))) // 统计词频
  //Map(world -> 1, hello -> 3)

偏函数

/*
偏函数：被包在花括号内没有 match的一组Case语句
 */

object PartitalFunctionApp extends  App{

  // 第一个输入参数类型，第二个是返回类型
  def sayChinese:PartialFunction[String,String] ={
        case "Akiho Yoshizawa" => ("吉老师。。。。")
        case "YuiHatang" => ("波老师。。。")
        case _ => ("不知道你们在说什么")
  }
  println(sayChinese("Akiho Yoshizawa"))
}

隐式转换

需求：为一个已存在的类添加一个新的方法（第三方的类）

• java: 动态代理
• Scala: 隐式转换

隐式转换测试

object ImplicitApp  extends  App {

  // 定义隐式转换函数
  implicit def man2superman(man:Man): Superman = new Superman(man.name)

  val man = new Man("PK")
  man.fly()

  implicit def file2richFile(file:File): RichFile = new RichFile(file)
  val file = new File(path+"\\hello.txt")
  println(file.read())
}

class Man(val name:String){
  def eat()={
    println(s"man [ $name ] eat....")
  }
}

class Superman(val name:String){
  def fly()={
    println(s"superman [ $name ] fly....")
  }
}

class RichFile(val file:File){
  def read()={
    scala.io.Source.fromFile(file.getPath).mkString
  }
}

隐式参数

指的是在函数或者方法中，定义一个用 implicit修饰的参数，此时Scala会尝试找到一个指定类型的，用 implicit修饰的对象，即隐式值，并注入参数

def testParam(implicit  name:String)={
  println(name + "~~~~~~~~~")
}
//testParam("张三")
implicit  val name1 = "implicit_name" // 这里需要注意，不可以定义多个隐式参数
testParam

隐式类

object ImplicitClassApp extends App {
  implicit class Calculator(x:Int){
    def add(a:Int) = a+x
  }
  println(12.add(3)) // 可以不创建对象，直接调用类中的方法
}

操作外部数据

读取文件

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


    val file = Source.fromFile(path+"\\hello.txt")(scala.io.Codec.UTF8)

    // 按行读取
    def readLine(): Unit ={
      for(line <- file.getLines())
        println(line)
    }
    // 按字符读
    def readChar(): Unit ={
      for(ele <- file){
        println(ele)
      }
    }

    // 读取网络
    def readNet(): Unit ={
      val file = Source.fromURL("http://www.baidu.com")
      for(line <- file.getLines())
        println(line)
    }
    readNet()
  }