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对于我的任务，我要编写一个文件，该文件使用试验的输入来确定一个人通过打开汽水瓶盖并查看他们是否中奖来获得奖品的平均值。他们有五分之一的机会获胜。一旦我获得了单独试验的平均值，我将重新读取试验并计算平均值。我在尝试从文件中读取双打时遇到了麻烦。到目前为止，这是我的代码。

import java.util.Scanner;
import java.io.File;
import java.io.PrintWriter;
import java.io.IOException;
public class BottleCapPrize
{
public static void main(String[] args) throws IOException
{
  double averageBottles = 0.0;
  double randNum = 0.0;
  int bottleSum = 0;
  int numBottles = 1;
  int bottle = 0;
  int maxRange = 6;
  int minRange = 1;
  int oneTrial = 0;
  int winPrize = 1;
  double token = 0;
  int totalSumCaps = 0;
  Scanner in = new Scanner(System.in);

  //Generates bottle number for first test
  randNum = Math.random();
  bottle = ((int)((randNum) * (maxRange - minRange)) + minRange);

  //construct an object called outFile to allow access to output methods of the PrintWriter class  
  PrintWriter outFile = new PrintWriter(new File("trials.txt"));

  //Gets users input for how many trials
  System.out.print("Enter the amount of trials: ");
  int trials = in.nextInt();
  System.out.println();

  //Check averages for entered trials
   for (int loop = 1; loop <= trials; loop++)    
  {
      //Clears out the loops variables each time through
     if(loop != 0)
    {
         averageBottles = 0;
         bottleSum = 0;
         oneTrial = 0;
         numBottles = 0;
    }
     for(int x = 1; x <= 20; x++)
    {
       if(x == 20) //One trial is completed
      {
       averageBottles = bottleSum / x;
       //Replaces the old bottle number for a new bottle
        randNum = Math.random();
        bottle = ((int)((randNum) * (maxRange - minRange)) + minRange);
      }
      else if(bottle == winPrize)
      {
        oneTrial = numBottles;
        if(oneTrial == 0)
        {
            oneTrial = 1;
        }
        //Replaces the old bottle number for a new bottle
        randNum = Math.random();
        bottle = ((int)((randNum) * (maxRange - minRange)) + minRange);
      }
      else if(bottle != winPrize) //not a winner, gets new bottle and increments the number of bottles tested
      {
       //Replaces the old bottle number for a new bottle
       randNum = Math.random();
       bottle = ((int)((randNum) * (maxRange - minRange)) + minRange);
       oneTrial = numBottles;
       numBottles ++;
      }
      bottleSum += oneTrial; //Adds the sum from each trial
    }
     outFile.println("Trial " + loop + "." + " " + averageBottles); //Prints the averages to the file
     System.out.println("Trial " + loop + "." + " " + averageBottles);
     //outFile.println("Trial " + "=" + " " + averageBottles); //Prints the averages to the file
     //System.out.println("Trial "+ "=" + " " + " " + averageBottles);
  }//end of for loop
  outFile.close ( );//close the file when finished 

  //Read the trial data back in and calculate the average
  File fileName = new File("trials.txt");
  Scanner inFile = new Scanner(fileName);

  //read file and get data
  while(inFile.hasNext())
  {
     token = inFile.nextDouble();
     totalSumCaps += token;
  }
  inFile.close();

  double totalAverageCaps = totalSumCaps / trials;
  //Print results
  System.out.println();
  System.out.println("The average number of caps opened in order to win a prize is: " + totalAverageCaps);
}

}

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1 回答 1

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如果您询问如何读取 aString并将其转换为 a double，那么您需要做的就是使用next()from Scanner，它返回 a String。然后，您可以使用Double.parseDouble(String s)将您的转换String为double. 或者你可以使用nextDouble()from Scanner。

不确定您是否已经学习过异常处理，但如果是，您可以使用try-catch块来捕获可能的NumberFormatException. 另外，如果你学过方法，你应该使用它们，也就是说，你应该在你的 main 中使用尽可能少的代码。您可以使用方法使您的代码更清晰。

编辑：您收到InputMismatchExceptionfromnextDouble()因为您正在阅读的令牌不是double.

于 2013-11-01T00:57:08.537 回答