java - 将 double 写入文件的问题，什么都不写

Question

在将 double 写入文本文件时，我似乎遗漏了一些东西，当我检查文件时，只存在空白。当我从文件中读取并使用 System.out.println() 打印时；它什么都不打印...这里出了什么问题？我需要做一些转换吗？

import java.io.*;
import javax.swing.JOptionPane;

public class ReadCalcAveragePrint  {

    double firstNum;
    double secondNum;
    double average;

    public void readFile() {

        try {
            File f = new File("numbers.txt");
            BufferedReader br = new BufferedReader(new FileReader(f));
            String one = br.readLine();
            String two = br.readLine();
            firstNum = Double.parseDouble(one);
            secondNum = Double.parseDouble(two);

            average = (firstNum + secondNum) / 2;
            JOptionPane.showMessageDialog(null, average, "title", JOptionPane.PLAIN_MESSAGE);

        } catch (Exception e) {
            e.printStackTrace();
            System.out.println(e);
        }

    }

    public void writeFile() {
        try {
            File f = new File("result.txt");
            FileOutputStream fos = new FileOutputStream(f);
            DataOutputStream dos = new DataOutputStream(fos);
            dos.writeDouble(average);
            dos.flush();
            fos.close();
            System.out.println("Printed.");
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println(e);

        }
    }

    public void readResult() {

        try {
            File f = new File("result.txt");
            BufferedReader br = new BufferedReader(new FileReader(f));
            String one = br.readLine();
            System.out.println(one);

        } catch (Exception e) {
            e.printStackTrace();
            System.out.println(e);
        }

    }

    public static void main(String[] args) {

        new ReadCalcAveragePrint().readFile();
        new ReadCalcAveragePrint().writeFile();
        new ReadCalcAveragePrint().readResult();
    }
}

Answer 1

在 main 中，您创建了 3 个不同的对象，只有第一个对象包含您从文件中读取的数字。

您应该只创建并重用一个对象:

public static void main(String[] args) {
    ReadCalcAveragePrint obj = new ReadCalcAveragePrint();
    obj.readFile();
    obj.writeFile();
    obj.readResult();
}

您还使用 DataOutputStream 编写结果文件，这意味着以二进制形式写入数据。如果您只想将结果保存为文本，您应该改用 FileWriter:

File f = new File("result.txt");
FileWriter fw = new FileWriter(f);
fw.write(String.valueOf(average));
fw.close();