Question

我有一个名为“readStock”的函数，它应返回[String，WeatherReading]类型的值，而“WeatherReading”是案例类“WeatherReadingStub”的对象。我不知道如何为函数“readStock”声明和返回对象。

代码： -

package HW9

object WeatherStub {
    //Setting file name
    val fileName = "weather.csv"
    //Calling Main
    def main(args: Array[String]): Unit = {
        val weatherData: Map[String, WeatherReading] = readWeather(fileName)
            printWeather(weatherData)
        }
        def readWeather(fn: String): Map[String,WeatherReading] = {
            //Creating a mutable map to collect all the values
            val weatherMuteMap = scala.collection.mutable.Map[String, WeatherReading]()
            //Checking for empty or null values
            def IsEmptyOrNull(s: String): Option[Float] = {
                if ((s ne null) && s.trim.length > 0) Some(s.toFloat) else None
            }
            //Reading file 
            for (line <- io.Source.fromFile(fn).getLines()) {
                val list1 = line.split(",", -1).map(_.trim).toList
            //Setting up default values
            val TotalPrecp: Option[Float] = IsEmptyOrNull(list1(1).toString) match { case Some(i) => Some(i) case _ => None}
            val LowPrecp: Option[Float] = IsEmptyOrNull(list1(2).toString) match { case Some(i) => Some(i) case _ => None}
            val HighPrecp: Option[Float] = IsEmptyOrNull(list1(3).toString) match { case Some(i) => Some(i) case _ => None}

            //Creating object for the case class WeatherReadingStub
            val WeatherReading = WeatherReadingStub(TotalPrecp,LowPrecp,HighPrecp)

            //Adding elements to the mutable list
            weatherMuteMap(list1(0).toString) = WeatherReading.toString
        }
        //Converting to Immutbale Map
        weatherMuteMap.toMap
    }


    def printWeather(weatherMap: Map[String, String]): Unit = {
        //Format of the message to be printed
        println("(Date,{Precipitation,LowTemperature,HighTemperature})\tAverageTemperature")

        //Printing the average temp values calculated in Case Class using object
        weatherMap.toSeq.sortBy(_._1).foreach(wd => println(wd + "\t" + wd._2.averageTemperature.getOrElse("N/A")))
        println

    }

}

案例类代码： -

package HW9

case class WeatherReadingStub(precipitation: Option[Float], lowTemperature: Option[Float], highTemperature: Option[Float]) {

    def averageTemperature: Option[Float] = (lowTemperature, highTemperature) match {case (Some(i),Some(j)) =>  Some((i + j)/2) case _ => None}

    override def toString: String = s"{${precipitation.getOrElse("MISSING")},${lowTemperature.getOrElse("MISSING")},${highTemperature.getOrElse("MISSING")}}"
}

Answer 1

检查您的班级名称WeatherReadingStub。在Object WeatherStub中， readWeather方法使用键构建一个可变的Map，日期（类型为String），value是WeatherReading对象。您的类WeatherReadingStub具有averageTemperature，并且您在MAP [String，WeatherReadingStub]中引用了WeatherReadingStub。如果将WeatherReading替换为已定义的对象WeatherReadingStub，则此程序将运行。你对MAP的定义应该是 val weatherData：Map [String，WeatherReadingStub] = readWeather（fileName）（替换所有其他出现次数。）

Scala返回Map方法的Object类型

1 个答案: