//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")
}