Why when I open the output.txt file, is strange code there, not 3.1

Question

i almost copy the example from "think in java book" chapter 11
however, the result "output.txt file" when opened by notepad of windows xp, always only very strange code inside, not what i want
do i need open the file, before i want to write?
or i use a wrong api again?
or the java code norm is very difference from ms windows?
thanks
import java.util.Random;
import java.io.*;
class CreatRandomFile
     public static void main(String args[])throws IOException
          File fileOutput=new File("output.txt");
          DataOutputStream out2=
               new DataOutputStream(
                    new BufferedOutputStream(
                         new FileOutputStream(fileOutput)));
          out2.writeDouble(3.1);
          out2.close();
     }//end main
}//end class

Answer 1

There are basically two ways of IO:
a) human readable format;
b) machine readable format;
What you've just done is writing a double value in machine readable
format to a file. Some folks call it 'binary format'. I bet your file is eight
byes long. A DataOutputStream writes data in machine readable
format. You need a PrintStream instead if you (a being human I suppose)
want to be able to read the contents of that file.
kind regards,
Jos