Error with file R/W?

Question

I'm trying to make a program that writes to a file, and reads it, then finds the average:

     public static void main(String[] args) throws IOException {
        writeToFile("C:\\scores.txt");
    }
    public static void writeToFile (String filename) throws IOException {
      BufferedWriter outputWriter = new BufferedWriter(new FileWriter(filename));
      Scanner sc = new Scanner(System.in);
    int i=0;
    int q=0;
      while(i >=0&&q<=20) {
         System.out.print("Enter Grade:");
          i=sc.nextInt();
          outputWriter.write(i);
          outputWriter.newLine();
         q++;
      }
      outputWriter.flush();
      outputWriter.close();
      processFile(filename);
    }
    public static void processFile (String filename) throws IOException, FileNotFoundException {

        try (BufferedReader inputReader = new BufferedReader (new InputStreamReader(new FileInputStream(filename)))) {
            String line;
            int lines=0;
             int intValue= 0;
             int sum = 0;
            while (( line = inputReader.readLine()) != null){
                intValue = Integer.parseInt(line);
              String sumStr;

              while((sumStr = inputReader.readLine()) != null) {
              sum = Integer.parseInt(sumStr);
              intValue = sum + intValue;
           lines++;
              }
          intValue=sum+intValue;

            }    
System.out.println(intValue/lines);
inputReader.close();
        }
}
}

Issue is, when I run this, it gets to the 21st grade(Supposed to end at 20) and gives me this error:

  Exception in thread "main" java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:481)
    at java.lang.Integer.parseInt(Integer.java:527)
    at scorereaderwriter.ScoreReaderWriter.processFile(ScoreReaderWriter.java:48)
    at scorereaderwriter.ScoreReaderWriter.writeToFile(ScoreReaderWriter.java:34)
    at scorereaderwriter.ScoreReaderWriter.main(ScoreReaderWriter.java:18)
    Java Result: 1

What am I doing wrong here?

Answer 1

Your program fails as soon as it attempts to run parseInt, because your inputReader.readLine() is returning nothing. What you could do is use inputReader.read() to get the integer value.

So for example:

int sum = 0;
while((sum = inputReader.read()) != -1) {
    intValue = sum + intValue
}

This should save you from having to read the file, convert the integer to string, then convert back to an integer again.

Edit: Also, check your first while loop, it runs 21 times instead of 20.