Question

If I have some binary data D And I convert it to string S. I expect than on converting it back to binary I will get D. But It’s wrong.

public class A {
    public static void main(String[] args) throws IOException {
        final byte[] bytes = new byte[]{-114, 104, -35};// In hex: 8E 68 DD
        System.out.println(bytes.length);               //prints 3
        System.out.println(new String(bytes, "UTF-8").getBytes("UTF-8").length); //prints 7
    }
}

Why does this happens?

Answer 1

Converting between a byte array to a String and back again is not a one-to-one mapping operation. Reading the docs, the String implmentation uses the CharsetDecoder to convert the incoming byte array into unicode. The first and last bytes in your input byte array must not map to a valid unicode character, thus it replaces it with some replacement string.