Scala学习笔记——内建控制结构

    //常见的写法
    var filename = "name"
    if (!args.isEmpty)
      filename = args(0)

    //比较简洁的写法
    var filename1 =
      if (!args.isEmpty) args(0)
      else "name"

    //更简洁的写法，不要有中间变量
    println(if(!args.isEmpty) args(0) else "name")

    //列出当前目录的文件和文件夹
    val filesHere = (new java.io.File(".")).listFiles

    for (file <- filesHere)
      println(file)

    //打印1到4
    for (i <- 1 to 4)
      println(i)

    //打印1到3
    for (i <- 1 until 4)
      println(i)

    //for循环中的过滤功能
    for (file <- filesHere if file.getName.endsWith("project"))
      println(file)

    //for循环中的过滤功能，多个条件用；号分隔
    for (file <- filesHere
         if file.isFile;
         if file.getName.endsWith("sbt")
    ) println(file)

    //嵌套枚举
    for( a <- 1 to 3; b <- 1 to 3){
      println( "Value of a: " + a );
      println( "Value of b: " + b );
    }

    //for循环采用yield,可以从存储中返回for循环中的变量的值，输出List(1, 2, 4, 5, 6, 7)
    val numList = List(1,2,3,4,5,6,7,8,9,10)
    System.out.println(
      for{
        a <- numList if a != 3; if a < 8
      }yield a
    )

//抛出异常
  def isEven(n : Int): Unit ={
    val half =
      if (n % 2 == 0) n / 2
      else throw new RuntimeException("n必须是偶数")
  }

　　val file = new FileReader("input.txt")
    try {
      //使用文件
    } catch {
      //捕获异常
      case ex: FileNotFoundException =>
      case ex: IOException =>
    } finally {
      //确保文件关闭
      file.close()
    }

//try-catch-finally语句的返回值
  def urlFor(path:String) =
    try{
      new URL(path)
    }catch{
      case e:MalformedURIException => new URL("www.scala-lang.org")
    }

    //匹配表达式
    val firstArg = if (args.length > 0) args(0) else ""
    firstArg match {
      case "1" => println("A")
      case "2" => println("B")
      case "3" => println("C")
      case _ => println("D")
    }