Kotlin的枚举与异常示例详解

enum class Color(val r: Int,val g: Int,val b: Int){
 //彩虹色也是一个典故：韦克菲尔德战役
 RED(255,0,0),ORANGE(255,165,0),YELLOW(255,255,0),
 GREEN(0,255,0),BLUE(0,0,255),INDIGO(75,0,130),VIOLET(238,130,238);
 
 fun rgb() = (r * 255 + g) * 256 + b
}

fun main() {
 println("RED's RGB value is ${Color.RED.rgb()}")

//枚举和when的配合使用
fun getMnemonic(color: Color): String{

 //when配合枚举使用
 return when(color){
  Color.RED -> "Richard"
  Color.ORANGE -> "Of"
  Color.YELLOW -> "York"
  Color.GREEN -> "Gave"
  Color.BLUE -> "Battle"
  Color.INDIGO -> "In"
  Color.VIOLET -> "Vain!"
 }
}

//when的多个case同一个结果的方式
fun getWarmth(color: Color) = when(color){
 Color.RED,Color.ORANGE,Color.YELLOW -> "warm"
 Color.GREEN -> "neutral"
 Color.BLUE,Color.INDIGO,Color.VIOLET -> "cold"
}

fun mix(c1: Color,c2: Color) =
 when(setOf(c1,c2)){
  setOf(Color.RED,Color.YELLOW) -> Color.ORANGE
  else -> throw Exception("Dirty Color")
 }

fun mixOptimized(c1: Color,c2: Color) =
  when{
   (c1 == Color.RED&& c2 == Color.YELLOW ||
     c2 == Color.RED&& c1 == Color.YELLOW) -> Color.ORANGE
   else -> throw Exception("Dirty Color")
  }

fun eval(e: Expr): Int =
  when(e){
   is Num -> e.value
   is Sum -> eval(e.right) + eval(e.left)
   else -> throw IllegalArgumentException("Unknown expression")
  }

fun recognize(c: Char) = when(c){
 in '0'..'9' -> "It's a digit!"
 in 'a'..'z',in 'A'..'Z' -> "It's a letter"
 else -> "I don't know what it is."
}

//将读取到的字符串类型转化成Int类型
fun readNumber(reader: BufferedReader): Int?{
  try {
   val line = reader.readLine()
   return Integer.parseInt(line)
  }catch (e: NumberFormatException){
   return null
  }finally {
   reader.close()
  }
}

fun readNumber2(reader: BufferedReader){
 val number = try {
  val line = reader.readLine()
  Integer.parseInt(line)
 }catch (e: NumberFormatException) {
  return
 }
 println(number)
}