Question

我正在编写一个程序来读取文本文件中的数据（成绩），计算平均值，然后将每个等级和数据分成两类：好的和差的（取决于低于还是高于平均值）< / p>

public static void main(String[] args) throws IOException {
    FileInputStream fis = new FileInputStream ("scores.txt");
    Scanner read = new Scanner (fis);
    int count=0, id;
    double total=0,average, grade;
    String line;
    Scanner stringScanner;
    while(read.hasNextLine()){
        line = read.nextLine();
        stringScanner = new Scanner(line);
        id = stringScanner.nextInt();
        while (stringScanner.hasNextDouble()){
            total = total + stringScanner.nextDouble();
            count++;
        }
        stringScanner.close();
    }
    average = total/count;
    System.out.println("The average is : "+ average);
    read.close();

    fis = new FileInputStream ("scores.txt");
    read = new Scanner (fis);
    while(read.hasNextLine()){
        line=read.nextLine();
        stringScanner=new Scanner (line);
        id = stringScanner.nextInt();
        while (stringScanner.hasNextDouble()){
            grade = stringScanner.nextDouble();
            if(grade >= average){
                FileOutputStream fos = new FileOutputStream("good.txt");
                PrintWriter pr = new PrintWriter (fos);
                pr.print(id + "/t"+ grade);
                pr.println();
            }
            else if (grade<average){
                FileOutputStream fos = new FileOutputStream("poor.txt");
                PrintWriter pr = new PrintWriter (fos);
                pr.print(id + "/t"+ grade);
                pr.println();
            }
            else System.out.println("test");
        }
        stringScanner.close();
    }
    fis.close();
    read.close();
    System.out.println("Files have been created...");
}

我认为我在计算平均值方面做得很好（因为它正确输出）。但是，我在编写好的和好的文本文件时遇到了麻烦，这些文件被创建但它们仍然是空的。如何让程序写入两个文件以及我的代码中究竟缺少什么？谢谢。

编辑：以下是.txt文件的外观：

206527     44.24
208530     75.38
207135     85.61
205241     91.51
204324     50.61
203357     68.28
202117     57.11

Answer 1

简而言之：发生这种情况是因为您未在close() 上致电PrintWriter。除此之外，如果你每次想要添加内容时都不打开文件，它显然会更有效。在开头打开两个文件，然后写入它们。完成工作后，请记得关闭所有已打开的内容。以下是您的计划的第二部分：

fis = new FileInputStream("scores.txt");
read = new Scanner(fis);
FileOutputStream fosGood = new FileOutputStream("good.txt");
PrintWriter prGood = new PrintWriter(fosGood);
FileOutputStream fosPoor = new FileOutputStream("poor.txt");
PrintWriter prPoor = new PrintWriter(fosPoor);
while (read.hasNextLine()) {
    line = read.nextLine();
    stringScanner = new Scanner(line);
    id = stringScanner.nextInt();
    while (stringScanner.hasNextDouble()) {
        grade = stringScanner.nextDouble();
        if (grade >= average)
            prGood.println(id + "\t" + grade);
        else if (grade < average)
            prPoor.println(id + "\t" + grade);
        else System.out.println("test");
    }
    stringScanner.close();
}
prGood.close();
prPoor.close();
fis.close();
fosGood.close();
fosPoor.close();
read.close();
System.out.println("Files have been created...");

此外，您不应该从main方法中抛出任何异常，而应将代码置于try/catch/finally块中。在这种情况下，关于关闭文件的所有代码都会进入finally。您可以选择使用try-with-resources statement。

Java：读取数据并比较然后写入

1 个答案: