[OS] Lab 01 - Problem 3

import java.io.*;
import java.nio.charset.StandardCharsets;

public class HW01_3 {
    public static void main(String[] args) {
        try {
            //Read text from command line and make a new text file with that input.
            File in = new File("source.txt"); //File will be named 'source.txt'
            String text;
            //If file manually created with text, skips the next block. If it was never created then :
            if(!in.exists()) { // - we create it. In the file we write whatever we read from command line.
                BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
                text = bf.readLine();

                PrintWriter pw = new PrintWriter("source.txt");
                pw.println(text);
                pw.close();
            } // Now we have a file created it it already didn't exist.


            //Actual code required by lab.
            //We don't declare the input file again as its delcared above as 'in' - we just use it from now on.
            File out = new File("destination.txt"); //Destination file where we print. :)
            BufferedReader br = new BufferedReader(new FileReader(in));
            BufferedWriter bw = new BufferedWriter(new FileWriter(out));

            String reversed = new StringBuilder(br.readLine()).reverse().toString();
            bw.write(reversed);

            br.close();
            bw.close();
        }
        catch (IOException e) {
            e.printStackTrace();
        }
        System.exit(0);
    }
}