writing to and reading from binary file java

Question

I am compressing a text file using Huffman code I generated then I converted all characters to string of 0's and 1's. Wrote them in file using following code. (Input was 1011001110010011 )

public static void writeToFile(String binaryString, BufferedWriter writer) throws IOException{
    int pos = 0;
    while(pos < binaryString.length()){
        byte nextByte = 0x00;
        for(int i=0;i<8 && pos+i < binaryString.length(); i++){
            nextByte = (byte) (nextByte << 1);
            nextByte += binaryString.charAt(pos+i)=='0'?0x0:0x1;
        }
        writer.write(nextByte);
        pos+=8;
    }
}

Then I tried to regenerate previous binary string 1011001110010011 from the file I just created, using following code

data = Files.readAllBytes(path);
for(int i=0;i<data.length;i++){
    byte nextByte = data[i];
    String tempString = "";
    for(int j=0;j<8; j++){
        byte temp = (byte) (0x1 & nextByte);
        if(temp==0x1){
            tempString="1".concat(tempString);
        }else if(temp==0x0){
            tempString="0".concat(tempString);
        }
        nextByte = (byte) (nextByte >> 1);
    }
    binary=binary.concat(tempString);  
}

But I got 111011111011111010110011111011111011111010010011 in output, I was just expecting some attached 0's.

Edit: made change in from string to binary code, now its adding 0's at end to complete byte.

public static void writeToFile(String binaryString, BufferedWriter writer) throws IOException{
    int pos = 0;
    while(pos < binaryString.length()){
        byte nextByte = 0x00;
        for(int i=0;i<8; i++){
            nextByte = (byte) (nextByte << 1);
            if(pos+i < binaryString.length())
                nextByte += binaryString.charAt(pos+i)=='0'?0x0:0x1;
        }
        writer.write(nextByte);
        pos+=8;
    }
}

Answer 1

The problem is that BufferedWriter.write() writes a char , not a byte . Whenever you're writing to the file, you're writing a variable-sized unicode character, not a single byte , so you're ending up with much more stored in your file than you were expecting.

You want to use

new BufferedOutputStream(new FileOutputStream("filename"))

instead, and change the signature of your method to take an OutputStream .

(You might notice that OutputStream.write() takes an int rather than a byte , but that is just there to confuse you... it actually writes only the low-order byte, rather than the whole int , so it does what you want.)