無法在scala程序中打印

Question

下面的scala代碼顯示沒有輸出，請幫我修正。我剛接觸scala.I嘗試打印一個Rational類實例。

object Test{ 

    def main() { 
     var r = new Rational(2,3) 
     println(r) 
     println("Hello") 
     //println(Rational(2,3).add(Rational(3,3))) 
    } 

} 

class Rational(n:Int,d:Int) 
{ 

    val num:Int =n 
    val den:Int =d 
    val sum :Int =num+den 
    def add(that:Rational):Rational={ 
     return new Rational(num*that.den+den*that.num,den*that.den) 
    } 

    override def toString(): String = num + "/" + den 

} 

object Rational { 
    def apply(n:Int,d:Int)=new Rational(n,d) 
} 

Answer 1

變化def main()到def main(args: Array[String])，JVM將無法識別沒有正確的參數類型