CODEWITHSUNDEEP
java
Rohan
Rohan

Reputation: 1657

How do you write any ASCII character to a file in Java?

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 '?'

Upvotes: 2

Views: 7958

Answers (3)

Stephen C
Stephen C

Reputation: 718886

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.

(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.)

Upvotes: 3

RedComet
RedComet

Reputation: 1202

Java strings are based on 16 bit wide characters, it tries to perform conversions around that assumption if there is no clear specifications.

The following sample code, write and reads data directly as bytes, meaning 8-bit numbers which have an ASCII meaning associated with them.

import java.io.*;
public class RWBytes{
    public static void main(String[] args)throws IOException{
        String filename = "MiTestFile.txt";
        byte[] bArray1 =new byte[5];
        byte[] bArray2 =new byte[5];
        bArray1[0]=65;//A
        bArray1[1]=66;//B
        bArray1[2]=67;//C
        bArray1[3]=68;//D
        bArray1[4]=69;//E
        FileOutputStream  fos = new FileOutputStream(filename);
        fos.write(bArray1);
        fos.close();
        FileInputStream fis = new FileInputStream(filename);
        fis.read(bArray2);
        ByteArrayInputStream bais = new ByteArrayInputStream(bArray2);
        for(int i =0; i< bArray2.length ; i++){
            System.out.println("As the bytem value: "+ bArray2[i]);//as the numeric byte value
            System.out.println("Converted as char to printiong to the screen: "+ String.valueOf((char)bArray2[i]));
        }   
    }
}

A fixed subset of the 7 bit ASCII code is printable, A=65 for example, the 10 corresponds to the "new line" character which steps down one line on screen when found and "printed". Many other codes exist which manipulate a character oriented screen, these are invisible and manipulated the screen representation like tabs, spaces, etc. There are also other control characters which had the purpose of ringing a bell for example.

The higher 8 bit end above 127 is defined as whatever the implementer wanted, only the lower half have standard meanings associated.

For general binary byte handling there are no such qualm, they are number which represent the data. Only when trying to print to the screen the become meaningful in all kind of ways.

Upvotes: 1

Luis Casillas
Luis Casillas

Reputation: 30227

You need to make up your mind what are you really doing. Are you trying to write some bytes to a file, or are you trying to write encoded text? Because these are different concepts in Java; byte I/O is handled by subclasses of InputStream and OutputStream, while character I/O is handled by subclasses of Reader and Writer. If what you really want to write is bytes to a file (which I'm guessing from your mention of compression), use an OutputStream, not a Writer.

Then there's another confusion you have, which is evident from your mention of "ASCII characters from 0-255." There are no ASCII characters above 127. Please take 15 minutes to read this: "The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)" (by Joel Spolsky). Pay particular attention to the parts where he explains the difference between a character set and an encoding, because it's critical for understanding Java I/O. (To review whether you understood, here's what you need to learn: Java Writers are classes that translate character output to byte output by applying a client-specified encoding to the text, and sending the bytes to an OutputStream.)

Upvotes: 1

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