Question

i can’t figure out about working with I/O.

I am using this code to read from file:

if (file.length() > Integer.MAX_VALUE) {
    throw new IllegalArgumentException("File is too large: " + file.length());
}

int len = (int) file.length();
System.out.println("failo dydis yra = "+len);
FileInputStream inputStream = new FileInputStream(file);

try {
    byte[] fileBits = new byte[len];
    for (int pos = 0; pos < len;) {
        int n = inputStream.read(fileBits, pos, len - pos);

        if (n < 0) {
            throw new EOFException();
        }
        pos += n;

    }
    for(int q=0; q<len; q++){
        char ch = (char)fileBits[q];
        int sk = (int)ch;
        System.out.println("symbol = "+fileBits[q]+" - "+ch+" - "+sk);
    }

When i read txt file then everything is nice but when i read not txt for example image i get similar result:

symbol = -78 - ﾲ - 65458
symbol = 52 - 4 - 52
symbol = -91 - ﾥ - 65445
symbol = 80 - P - 80
symbol = -118 - ﾊ - 65418
symbol = 76 - L - 76
symbol = 122 - z - 122
symbol = 78 - N - 78
symbol = 112 - p - 112
symbol = 97 - a - 97
symbol = 56 - 8 - 56
symbol = -112 - ﾐ - 65424

So i can’t figure why there are minus ? And why when i want to convert back i get this 65***.

Maybe i have to read different if i want to convert these bytes to chars, work with them and write again to file.

Thanks.

Answer 1

So i can’t figure why there are minus ?

In Java, a byte can have values between -128 and 127. Therefore, you’re seeing negative values. You can use 0xff & fileBits[q] to convert that to an integer value between 0 and 256.

And why when i want to convert back i get this 65***

Converting a byte into a char is meaningless unless the byte happens to be part of a string of ASCII characters in an ASCII-compatible encoding. What happens is that Java extends the byte’s first bit to a 16bit value. If the first bit happens to be set (i.e. the number is negative), the result will be a high 16 bit number, typically in the form of 65xxx.

Everything is working fine, just give the bytes to an image processing/display function. Note that your function is error-prone since it will needlessly fail if the file size changes while you’re reading the file. If you want to read a string, use a Reader object, for example an InputStreamReader.