Java：将输出打印到文本文件

Question

I am a beginner in coding. I am in an Intro to Programming and Algorithms course in my college. My professor and I cannot figure out how to fix this code. I am trying to output to a file from another file. The new file is created, but remains empty. Any help or input would be greatly appreciated! Thanks!

import java.util.Scanner;
import java.io.PrintWriter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class Part3 {
public static void main(String[] args) throws IOException
{
    int i = 0;

    FileInputStream fileIn = null;
    Scanner file = null;
    double input = 0;

    FileOutputStream fileOut = null;
    PrintWriter file2 = null;

    System.out.println("Opening file LabInput.txt.");
    fileIn = new FileInputStream("LabInput.txt");
    file = new Scanner(fileIn);

    fileOut = new FileOutputStream("LabOutput.txt");
    file2 = new PrintWriter(fileOut);

    while (file.hasNext())
    {
        input = file.nextDouble();
        file2.println("test");

            if(i % 3== 0)
            {
                 file2.println("");
                 i++;
            }
        file2.printf("%10.3f", input);
   }

    file2.println("");
    file2.println("Closing file LabInput.txt.");
    fileIn.close();
    fileOut.close();

}}

Answer 1

Add file2.close(); at the end of your program. OutputStreams often write to a buffer instead of the actual destination (here the file). This buffer is flushed when its full. To ensure that everything is written to the file, you have to call close() .