Question

Basically I’m trying to use a BufferedWriter to write to a file using Java. The problem is, I’m actually doing some compression so I generate ints between 0 and 255, and I want to write the character who’s ASCII value is equal to that int. When I try writing to the file, it writes many ? characters, so when I read the file back in, it reads those as 63, which is clearly not what I want. Any ideas how I can fix this?

Example code:

int a = generateCode(character); //a now has an int between 0 and 255
bw.write((char) a);

a is always between 0 and 255, but it sometimes writes ‘?’

Answer 1

You are really trying to write / read bytes to / from a file.
When you are processing byte-oriented data (as distinct from character-oriented data), you should be using InputStream and OutputStream classes and not Reader and Writer classes.

In this case, you should use FileInputStream / FileOutputStream, and wrap with a BufferedInputStream / BufferedOutputStream if you are doing byte-at-a-time reads and writes.

Those pesky ‘?’ characters are due to issues the encoding/decoding process that happens when Java converts between characters and the default text encoding for your platform. The conversion from bytes to characters and back is often “lossy” … depending on the encoding scheme used. You can avoid this by using the byte-oriented stream classes.

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(And the answers that point out that ASCII is a 7-bit not 8-bit character set are 100% correct. You are really trying to read / write binary octets, not characters.)