GSM 7bit (part of PDU) pack/encoding algorithm in Java

GSM 7bit (part of PDU) pack/encoding algorithm in Java. This can be used for SMS/USSD writing.

public static String stringTo7bit(String string) {
        String hex = "";
        byte[] bytes = string.getBytes();
        int f = 0;
        while (f < bytes.length - 1) {
            int t = (f % 8) + 1;
            if (t < 8) {
                byte b = (byte) (((bytes[f] >>> (t - 1)) |
                    (bytes[f + 1] << (8 - t))) & 0x000000FF);
                hex += intToHex(b & 0x000000FF).toUpperCase();
            }
            f++;
        }
        if ((f % 8) + 1 < 8)
            hex += intToHex((bytes[f] >>> (f % 8)) & 0x000000FF).toUpperCase();
        return hex;
    }

public static String intToHex(int i) {
        String hex = Integer.toHexString(i);
        if (hex.length() % 2 != 0) hex = 0 + hex;
        return hex;
    }

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