我正在看Apache Commons库中的一段代码，想知道这些条件到底能做什么。

public static byte[] decodeHex(final char[] data) throws DecoderException {

        final int len = data.length;

        if ((len & 0x01) != 0) { // what does this condition do
            throw new DecoderException("Odd number of characters.");
        }

        final byte[] out = new byte[len >> 1];

        // two characters form the hex value.
        for (int i = 0, j = 0; j < len; i++) {
            int f = toDigit(data[j], j) << 4;
            j++;
            f = f | toDigit(data[j], j);
            j++;
            out[i] = (byte) (f & 0xFF); // what is happening here.
        }

        return out;
    }

提前致谢。