FileWriter problem with 80 to 9F

Question

When writing ints to a file, whenever they are 80 to 9F (128 to 159 in decimal) then the FileWriter writes them as 3F (decimal 63). Does anyone know why this happens and how to fix it? Here's some test code I used
import java.io.*;
public class MyWriter
     public static void main(String args[])
          try
               FileWriter out = new FileWriter("temp");
               for (Integer i = 0; i < 256; i++)
                    out.write(i);
               out.close();
          catch(Exception e)
And the temp file's hex data was this:
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
Thanks
Krimson Eagl

Answer 1

if you want to know the reason for this behaviour, it is because "writers" and "readers"
work with Unicode characters instead of bytes. But because files on disks consist
of bytes rather than unicode characters, characters have to be mapped to bytes in
some way.
Mappings between characters and bytes are called "character encodings" and there are
several of them. For example the encoding used by MS Windows in western locales is called windows-1252.
You can see what it looks like in wikipedia
http://en.wikipedia.org/wiki/Windows-1252
One feature of Windows-1252 is that it lacks the characters in the range \u0080 -
\u009F. Because there is no mapping for these characters, you cannot write them
to disk. They get substituted by a "conversion error" byte 0x3F (the ASCII code of the question
mark). This is what you see in the output of your program.
On the other hand, if you use an outputstream rather than a writer, you are already
writing bytes disk and there is no need for a conversion from Unicode characters
to bytes.