Easiest
        Scanner in = new Scanner(new File("Files_entrada.txt"));
        System.out.println(line + ": " + in.nextLine());
        in.close();

        PrintWriter out = new PrintWriter("Files_salida.txt");
        out.println(line + ": " + Math.random());
        out.close();

Byte Streams

        in = new FileInputStream("input.txt");
        while ((c = in.read()) != -1) {

        out = new FileOutputStream("output.txt");
        out.write(c);

Character Streams	(most used)

         in = new FileReader("input.txt");
         while ((c = in.read()) != -1)
         
         out = new FileWriter("output.txt");
         out.write(c);

Character Streams	(POO)
         br = new BufferedReader(new FileReader("input.txt"));
         String contentLine = br.readLine();

         PrintWriter pw = new PrintWriter(new File("PrintWriterData.txt"));
         pw.print(i); // Escribe Strings
         pw.write(i); // Escribe tipos primitivos (int, etc)

