Design Pattern Example: Applying To A Real Project

Hey everyone! In this article, we're diving into how to apply design patterns in a real-world project. We'll cover the importance of choosing the right pattern and justify our design decisions. Drawing inspiration from teams F and C's 2022 projects and the detailed technical designs of 2023, let’s get started!

Introduction to Design Patterns

Design patterns are like pre-made blueprints for solving common design problems. They offer proven solutions, making our code more maintainable, flexible, and easier to understand. By using design patterns, we avoid reinventing the wheel and leverage the collective wisdom of experienced developers. It’s about writing code that not only works but is also elegant and scalable.

The Importance of Justification

Choosing a design pattern isn't just about picking one at random. It's crucial to justify why a particular pattern is the best fit for the problem at hand. A good justification shows that you've considered the trade-offs and understand the context of your application. It also helps others understand your design decisions, making collaboration smoother. Without a solid justification, you risk applying a pattern that doesn't quite fit, leading to unnecessary complexity and potential problems down the road.

Example: Applying the Strategy Pattern

Let's consider a scenario where we're building an e-commerce platform. One of the key features is calculating shipping costs. The shipping cost calculation varies depending on factors like destination, weight, and shipping method (e.g., standard, expedited, overnight). Without a design pattern, we might end up with a complex, hard-to-maintain conditional statement that handles all the different shipping calculation logic.

This is where the Strategy pattern comes in handy. The Strategy pattern allows us to define a family of algorithms (in this case, shipping cost calculation algorithms), encapsulate each one, and make them interchangeable. This enables us to vary the algorithm independently of the clients that use it. This is incredibly useful because it means we can easily add new shipping methods or modify existing ones without affecting the core logic of our e-commerce platform. You might ask, how exactly does this benefit our application?

Class Diagram

Here’s a simplified class diagram to illustrate the Strategy pattern:

[Context] -- [Strategy]
[ConcreteStrategyA] --|> [Strategy]
[ConcreteStrategyB] --|> [Strategy]

• Context: The ShippingCalculator class, which maintains a reference to a ShippingStrategy object.
• Strategy: An interface or abstract class defining the shipping cost calculation algorithm (e.g., ShippingStrategy).
• Concrete Strategies: Concrete classes that implement the ShippingStrategy interface, each representing a different shipping calculation algorithm (e.g., StandardShipping, ExpeditedShipping).

Implementation

Here's how we can implement the Strategy pattern in code (using a conceptual example):

// Strategy Interface
interface ShippingStrategy {
    double calculateCost(Order order);
}

// Concrete Strategies
class StandardShipping implements ShippingStrategy {
    @Override
    public double calculateCost(Order order) {
        // Calculate standard shipping cost based on order details
        return order.getWeight() * 0.10 + 5.0;
    }
}

class ExpeditedShipping implements ShippingStrategy {
    @Override
    public double calculateCost(Order order) {
        // Calculate expedited shipping cost based on order details
        return order.getWeight() * 0.25 + 10.0;
    }
    }

class OvernightShipping implements ShippingStrategy {
    @Override
    public double calculateCost(Order order) {
        // Calculate overnight shipping cost based on order details
        return order.getWeight() * 0.50 + 20.0;
    }
}

// Context
class ShippingCalculator {
    private ShippingStrategy strategy;

    public ShippingCalculator(ShippingStrategy strategy) {
        this.strategy = strategy;
    }

    public void setStrategy(ShippingStrategy strategy) {
        this.strategy = strategy;
    }

    public double calculateShippingCost(Order order) {
        return strategy.calculateCost(order);
    }
}

// Client Code
public class Main {
    public static void main(String[] args) {
        Order myOrder = new Order(10.0); // Order with 10.0 kg weight

        // Calculate shipping cost using standard shipping
        ShippingCalculator calculator = new ShippingCalculator(new StandardShipping());
        double standardCost = calculator.calculateShippingCost(myOrder);
        System.out.println("Standard Shipping Cost: " + standardCost);

        // Change the shipping strategy to expedited shipping
        calculator.setStrategy(new ExpeditedShipping());
        double expeditedCost = calculator.calculateShippingCost(myOrder);
        System.out.println("Expedited Shipping Cost: " + expeditedCost);

         // Change the shipping strategy to overnight shipping
        calculator.setStrategy(new OvernightShipping());
        double overnightCost = calculator.calculateShippingCost(myOrder);
        System.out.println("Overnight Shipping Cost: " + overnightCost);
    }
}

class Order {
    private double weight;

    public Order(double weight) {
        this.weight = weight;
    }

    public double getWeight() {
        return weight;
    }
}

Justification

Why did we choose the Strategy pattern? Here's the justification:

• Flexibility: The Strategy pattern allows us to easily add new shipping methods without modifying the ShippingCalculator class. This is crucial for accommodating future business requirements and integrations with different shipping providers.
• Maintainability: Each shipping calculation algorithm is encapsulated in its own class, making the code more modular and easier to maintain. Changes to one algorithm don't affect the others.
• Testability: Each strategy can be tested independently, ensuring the correctness of each shipping calculation algorithm.
• Open/Closed Principle: The Strategy pattern adheres to the Open/Closed Principle, which states that a class should be open for extension but closed for modification. We can add new strategies without modifying the existing ShippingCalculator class.

Without the Strategy pattern, we would likely end up with a large, complex conditional statement within the ShippingCalculator class. This would make the code harder to read, understand, and maintain. Adding new shipping methods would require modifying the existing code, potentially introducing bugs and increasing the risk of breaking existing functionality. The Strategy pattern provides a more elegant and scalable solution.

Specific Application to Our E-Commerce Platform

In our e-commerce platform, we anticipate integrating with multiple shipping providers, each with its own API and calculation methods. The Strategy pattern allows us to easily adapt to these different APIs by creating a separate strategy for each provider. We can also use the Strategy pattern to implement different pricing tiers based on customer loyalty or order volume. The flexibility of the Strategy pattern makes it a perfect fit for our evolving business needs.

Moreover, imagine offering promotions like free shipping on orders over a certain amount. With the Strategy pattern, implementing this promotion becomes straightforward. We can create a new strategy that applies a discount to the shipping cost based on the order total. This keeps our code clean and manageable, even as we add more promotional offers.

Benefits of Using Design Patterns

The Strategy pattern is just one example of how design patterns can improve the quality of our code. By using design patterns, we can:

• Improve Code Readability: Design patterns provide a common vocabulary for developers, making it easier to understand the structure and intent of the code.
• Reduce Code Complexity: Design patterns break down complex problems into smaller, more manageable parts.
• Increase Code Reusability: Design patterns can be reused across multiple projects, saving time and effort.
• Enhance Code Maintainability: Design patterns make it easier to modify and extend the code, reducing the risk of introducing bugs.

Conclusion

In conclusion, applying design patterns requires careful consideration and justification. The Strategy pattern is a powerful tool for managing different algorithms or behaviors in a flexible and maintainable way. By understanding the benefits of design patterns and justifying our design decisions, we can build robust, scalable, and maintainable applications. Remember, it’s not just about using a pattern; it’s about using the right pattern for the job and understanding why it’s the right choice. Keep coding, guys!