Generate a 6 digit code in Java (case-insensitive)

Java 6 digit unique code generator

    private static String getUniquedId(BloomFilter<String> filter) {
        String uid = getStringUid();
        while(filter.contains(uid)) {
            uid = getStringUid();
        }
        filter.add(uid);
        return uid;
    }

    private static String getStringUid() {
        UUID uid2 = UUID.randomUUID();
        return uid2.toString().substring(0, 6);
    }