Question

对于这个分配，我要编写一个代码来获取文件（Numbers.txt）并计算数字的平均值和标准差，并将它们打印到不同的文件（Results.txt）。我的代码编译得很好但是当我进入我的键盘输入Numbers.txt时，我收到一条错误信息。

以下是我的代码片段

filename = keyboard.nextLine();

File file = new File(filename);          //Create a FileReader object passing it the filename
Scanner inputFile = new Scanner(file);   
line = inputFile.nextLine();             //priming read to read the first line of the file
while (inputFile.hasNextDouble())        //create a loop that continues until you are at the end of the file
{   
sum += inputFile.nextDouble();         //convert the line into a double value and add the value to the sum
    count ++;                          //increment the counter
    inputFile.hasNext();              //read a new line from the file
}
inputFile.close();                     //close the input file
mean = (sum/count);                    //store the calculated mean


File file2 = new File(filename);          //Create a FileReader object passing it the filename
 Scanner inputFile2 = new Scanner(file2);  //reconnect to the FileReader object passing it the    filename
                                        //reconnect to the BufferedReader object passing it the   FileReader object.
sum = 0;                                  //reinitialize the sum of the numbers
count = 0;                                //reinitialize the number of numbers added
line = inputFile2.nextLine();            //priming read to read the first line of the file
while (inputFile2.hasNextDouble())       //loop that continues until you are at the end of the file
{                                
  sum += inputFile2.nextDouble();
inputFile2.nextDouble();
}
 difference = inputFile2.nextDouble() - mean;  //convert the line into a double value and subtract the mean
 sum += Math.pow(difference,2);             //add the square of the difference to the sum
    count ++;                                 //increment the counter
   if (inputFile2.hasNextDouble())
   inputFile2.hasNext();                      //read a new line from the file
   inputFile2.close();                         //close the input file
   stdDev = Math.sqrt(sum/count);             //store the calculated standard deviation

这是我得到的错误消息

java.util.NoSuchElementException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextDouble(Unknown Source)
at StatsDemo.main(StatsDemo.java:53)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)

我确定我的编码出现了很多错误，但我还没有足够的经验来注意它们。非常感谢帮助。

最后，让程序运行并计算平均值，但现在我有点困难找出如何使用nextDouble和减法均值。我相信我必须将线转换为双倍值。以下是我遇到麻烦的部分：

File file2 = new File(filename);          //Create a FileReader object passing it the filename
Scanner inputFile2 = new Scanner(file2);  //reconnect to the FileReader object passing it the filename
                                        //reconnect to the BufferedReader object passing it the    FileReader object.
sum = 0;                                  //reinitialize the sum of the numbers
count = 0;                                //reinitialize the number of numbers added
line = inputFile2.nextLine();            //priming read to read the first line of the file
while (inputFile2.hasNextDouble())       //loop that continues until you are at the end of the file
{                                
  sum += inputFile2.nextDouble();

 difference = inputFile2.nextDouble() - mean;  //convert the line into a double value and subtract the mean
 sum += Math.pow(difference,2);             //add the square of the difference to the sum
    count ++; 
}//increment the counter
   if (inputFile2.hasNextDouble())
   {
   inputFile2.hasNext();                      //read a new line from the file
   inputFile2.close();                         //close the input file
   stdDev = Math.sqrt(sum/count);             //store the calculated standard deviation            
   }

Answer 1

您关闭了Scanner :: inputFile，然后再次使用它。你可以想象，如果你关闭它就不能使用它！

Answer 2

将第47行从line = inputFile.nextLine();更改为line = inputFile2.nextLine();（as suggested by user1598503）后，您现在可以在第53行获得NoSuchElementException。

它基本上说你的扫描仪没有下一个双倍。这是非常合乎逻辑的，因为你在第48行有一个while循环，它循环直到它到达文件的末尾。因此，当您在while循环之后请求下一个double时，您位于文件的末尾，并且没有下一个double。 The Java docs explain quite clearly why NoSuchElementException被抛出。

您需要更改while循环。尝试更多地使用它和/或找到一个好的Java教程。我确定你是否花更多的时间来使你的计划有效。

祝你好运！

有打印/文件编写器的问题

2 个答案: