为什么这段代码写/打印所有 0.0 而不是不同的随机数？

Question

I'm trying to generate random numbers and write them to a file, then print them. Instead all zeros such as this 0.0 are printed by line in the console and in the file its written in ASCII code.

I have already tied using different java input classes and using the random number generator.

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;
import java.util.Random;


    public static void main(String[] args) throws IOException {
        makefile(10, "inputHW02.txt");

        double[] sizearray0 = new double[10];
        int i = 0;
        Scanner inFile;

        inFile = new Scanner(new File("inputHW02.txt"));

        while (inFile.hasNextDouble()) {
            sizearray0[i] = inFile.nextDouble();
            i++;
        }

        for (int r = 0; r < sizearray0.length; r++)
            System.out.println(sizearray0[r]);

        inFile.close();
    }

    public static void makefile(double n, String filename) throws IOException {

        FileOutputStream writer = new FileOutputStream(filename);
        DataOutputStream dos = new DataOutputStream(writer);
        Random rand = new Random();

        for (int i = 0; i < n; i++) {
            dos.writeInt((int) 60);
            ;

        }
        if (writer != null) {
            writer.flush();
            writer.close();
        }
    }

I expect the file and output console should have random numbers separated on a new line such as 10.0 23.0 1.0 and so forth.

Answer 1

The reason we use PrintWriter over DataOutputStream for writing to a file is better explained here .

public static void makefile(double n, String fileName) throws IOException {
    FileWriter fileWriter = new FileWriter(fileName);
    PrintWriter printWriter = new PrintWriter(fileWriter);
    Random rand = new Random();

    for (int i = 0; i < n; i++) {
        printWriter.println(rand.nextDouble());  // <--- observe this
    }
    if (printWriter != null) {
        printWriter.flush();
        printWriter.close();
    }
}

Also,

1. You were not using rand .
2. Use printWriter.println() that will take care of adding a newline character after each line is written to the file.

Answer 2

The DataInputStream / DataOutputStream classes read / write data in binary format. Whereas the Scanner reads the data in text format.

Which means you are writing the binary equivalent of integer 60 to the file, and while reading, you are trying to read the character string "60".

In short:

• Use DataInputStream if you are reading data written using DataOutputStream .
• Use Scanner or FileReader if you have used FileWriter for writing file.

Answer 3

Your code is not using rand. If I was in your situation, I would use a PrintWriter or BufferedWriter, it makes it simpler