Is below code a valid Singleton design pattern for Mongodb in Java?

Please suggest any improvements.

```
public class Mongo extends MongoClient {

    private static Mongo mongoClient = null;
    private static MongoDatabase mogoDB = null;

    private Mongo(ServerAddress server, List<MongoCredential> mongoCredentialList) {
        super(server, mongoCredentialList);
    }

    public static Mongo getMongoClient() {
        return getMongoClient("userName", "password", "127.0.0.1", 27017, "SampleDB");
    }

    public static Mongo getMongoClient(String userName, String pwd, String ip, int port, String dbName) {

        if (mongoClient == null) {

            logger.debug("******* Trying to connect to Mongo Server *******");

            ServerAddress server = new ServerAddress(ip, port);
            List<MongoCredential> mongoCredentialList = new ArrayList();
            char[] password = pwd.toCharArray();
            mongoCredentialList.add(MongoCredential.createCredential(userName, dbName, password));

            mongoClient = new Mongo(server, mongoCredentialList);

            logger.debug("******* Connected to the Mongo server Successfully *******");
        } else {
            logger.debug("Already connected to Mongo server...");
        }
        return mongoClient;
    }

    public static MongoDatabase getMongoDatabase() {

        if (mogoDB == null) {    
            logger.debug("******* Trying to get Mongo DB - SampleDB - connection. *******");
            mogoDB = getMongoClient().getDatabase("SampleDB");
            logger.debug("******* Successfully Connected to - SampleDB - Mongo DB *******");
        }
        return mogoDB;

    }

    public static MongoDatabase getMongoDatabase(String dbName) {

        if (mogoDB == null) {    
            logger.debug("******* Trying to get Mongo DB - " + dbName + " - connection. *******");
            mogoDB = getMongoClient().getDatabase(dbName);
            logger.debug("******* Successfully Connected to - " + dbName + " - Mongo DB *******");
        }
        return mogoDB;

    }
}

```