Question

Please see the code snippet below

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;

public class ReadFile {


    public static void main(String[] args)  {

        String str="";
        FileReader fileReader=null;

        try{


            // I am running on windows only  & hence the path :) 
            File file=new File("D:\\Users\\jenco\\Desktop\\readme.txt");
            fileReader=new FileReader(file);
            BufferedReader bufferedReader=new BufferedReader(fileReader);
            while((str=bufferedReader.readLine())!=null){
                System.err.println(str);
            }

        }catch(Exception exception){
            System.err.println("Error occured while reading the file : " + exception.getMessage());
            exception.printStackTrace();
        }
        finally {
            if (fileReader != null) {
                try {
                    fileReader.close();
                    System.out.println("Finally is executed.File stream is closed.");
                } catch (IOException ioException) {

                    ioException.printStackTrace();
                }
            }
        }

    }

}

When I execute the code multiple times , I get output randomly as below , sometimes the System.out statement gets printed first in the console , sometimes the System.err gets printed first. below are the random outputs that I get

Output 1

Finally is executed.File stream is closed.
this is a text file 
and a java program will read this file.

Output 2

this is a text file 
and a java program will read this file.
Finally is executed.File stream is closed.

Why is this so ?

Answer 1

I believe this is because you are writing to two different outputs (one is standard out and the other standard error). These are probably handled by two different threads at runtime to allow writing to both during java execution. Assuming this is the case, the cpu task scheduler is not going to execute the threads in the same order every time.

You should never get this functionality if all of your output is going to the same output stream (ie everything goes to standard out or everything goes to standard err). You will never be guaranteed execution order of standard error vs standard output.