Implement a function to check if a string/byte array follows utf-8 format

Question

I am trying to solve this interview question.

After given clearly definition of UTF-8 format. ex: 1-byte : 0b0xxxxxxx 2- bytes:.... Asked to wri

Answer 1

public static boolean validUTF8(byte[] input) {
    int i = 0;
    // Check for BOM
    if (input.length >= 3 && (input[0] & 0xFF) == 0xEF
            && (input[1] & 0xFF) == 0xBB & (input[2] & 0xFF) == 0xBF) {
        i = 3;
    }

    int end;
    for (int j = input.length; i < j; ++i) {
        int octet = input[i];
        if ((octet & 0x80) == 0) {
            continue; // ASCII
        }

        // Check for UTF-8 leading byte
        if ((octet & 0xE0) == 0xC0) {
            end = i + 1;
        } else if ((octet & 0xF0) == 0xE0) {
            end = i + 2;
        } else if ((octet & 0xF8) == 0xF0) {
            end = i + 3;
        } else {
            // Java only supports BMP so 3 is max
            return false;
        }

        while (i < end) {
            i++;
            octet = input[i];
            if ((octet & 0xC0) != 0x80) {
                // Not a valid trailing byte
                return false;
            }
        }
    }
    return true;
}