Getting Ready: Online Blackjack Game

Problem definition

Blackjack is a popular casino card game where multiple players compete individually against a dealer. The main objective is to have a hand value closer to 21 than the dealer without exceeding it (“busting”). The game uses one or more standard decks of cards. Each card has a specific value: number cards (2-10) are worth their face value, face cards (Jack, Queen, King) are worth 10 points, and the Ace can count as either 1 or 11, whichever benefits the hand most. The best possible hand, a “Blackjack,” consists of an Ace and a 10-point card (10, Jack, Queen, or King).

At the beginning of each round, players place bets, and players and the dealer deals two cards to each. Players’ cards are face up, while the dealer has one face up and one face down card. Players can choose to “hit” (draw an additional card) or “stand” (end their turn) in an attempt to get closer to 21 without busting. If a player’s total exceeds 21, they lose immediately. After all players have finished, the dealer reveals their hidden card and draws according to predefined rules. Winners are determined by comparing hand values: the player wins if their total is higher than the dealer’s without busting.

In this LLD interview case study, you’ll focus on:

• Modeling the core game mechanics of Blackjack, including card values, player and dealer actions (hit, stand), betting, and win/loss conditions.

• Designing an interactive flow for multiple players playing concurrently against the dealer, properly handling card dealing, turns, and bet outcomes.

• Ensuring the system can reliably manage hands, bets, and game state, while enforcing all Blackjack rules (such as Blackjacks, busts, ties, and dealer drawing rules).

• Building a foundation that can be extended for features like multiple tables, different deck sizes, or online multiplayer support.

Note: This system model is adaptable for online casinos, learning simulators, or any platform looking to provide a scalable Blackjack game experience.

The following slide represents how to play Blackjack:

Expectations from the interviewee

There are several components in a Blackjack game, each with specific constraints and requirements. The following provides an overview of some of the main expectations that the interviewer will want to hear you discuss in more detail during the interview.

Players in the game

To get a better understanding of the game and the players of the game, you may ask the interviewer the following set of questions:

1. How many players can play Blackjack?

2. Can players play the game against each other?

Point dynamics

The rules related to the number of points also need to be clarified by the interviewer; therefore, you may ask the questions listed below:

1. How many points can the player or the dealer hit the card?

2. What will happen if the dealer and the player get the same points?

Card limit

The interviewer would expect you to ask about the maximum number of cards the player can have. Therefore, you may ask a question listed below:

1. Is there a limit on the number of cards the player takes?

Design approach

We will design this online Blackjack game using a bottom-up design approach. To achieve this, we will follow these steps:

• First, we’ll identify and design the smallest, core entities such as Card, Hand, and Player (including the dealer as a special player), clarifying their responsibilities and interactions.

• Next, we’ll model the Deck, GameTable, and GameController to coordinate the game flow—dealing, betting, player actions, dealer logic, and determining results.

• We will incorporate game rules (card values, Blackjacks, busts, and win conditions) into these entities’ behaviors, ensuring correctness and clarity.

• We’ll ensure that the design allows for scalability, supporting multiple tables and concurrent games, and enforcing a clear separation of concerns for easy maintenance and extension.

• We’ll highlight how SOLID principles and relevant design patterns can help us achieve a clean, maintainable system.

Design pattern 

During an interview, discussing the design patterns that an online Blackjack game falls under is always a good practice. Stating the design patterns gives the interviewer a positive impression and shows that the interviewee is well-versed in the advanced concepts of object-oriented design.

Let’s explore the requirements of the online Blackjack game in the next lesson.