What Are Design Patterns?

Design patterns are proven, reusable solutions to common problems that arise in software design. They represent best practices evolved over time by experienced software developers. Rather than being finished code that you can copy and paste, design patterns are templates or blueprints that describe how to solve a problem in various situations.

Think of design patterns as the architectural blueprints of software development. Just as architects use established patterns for building structures (like how to design a doorway or window), software developers use design patterns to solve recurring design problems in a standardized way.

Why Design Patterns Matter

Design patterns offer several key benefits:

• Reusability: Patterns provide solutions that have been tested and proven in real-world scenarios
• Communication: They create a common vocabulary for developers to discuss design solutions
• Best Practices: They encapsulate years of collective programming wisdom
• Maintainability: Code following patterns is typically easier to understand and modify
• Scalability: Patterns help structure code in ways that accommodate growth

The Three Categories of Design Patterns

Design patterns are typically organized into three fundamental categories based on their purpose:

1. Creational Patterns

Creational patterns deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. They help make a system independent of how its objects are created, composed, and represented.

Common Creational Patterns:

• Factory Pattern: Creates objects without specifying the exact class of object that will be created
• Singleton Pattern: Ensures a class has only one instance and provides global access to it
• Builder Pattern: Constructs complex objects step by step
• Prototype Pattern: Creates new objects by copying existing ones
• Abstract Factory Pattern: Provides an interface for creating families of related objects

2. Structural Patterns

Structural patterns explain how to assemble objects and classes into larger structures while keeping these structures flexible and efficient. They focus on how classes and objects are composed to form larger structures.

Common Structural Patterns:

• Adapter Pattern: Allows incompatible interfaces to work together
• Decorator Pattern: Adds new functionality to objects dynamically
• Facade Pattern: Provides a simplified interface to a complex subsystem
• Proxy Pattern: Provides a placeholder or surrogate for another object
• Bridge Pattern: Separates an object’s interface from its implementation

3. Behavioral Patterns

Behavioral patterns are concerned with algorithms and the assignment of responsibilities between objects. They describe not just patterns of objects or classes but also the patterns of communication between them.

Common Behavioral Patterns:

• Observer Pattern: Defines a one-to-many dependency between objects
• Strategy Pattern: Defines a family of algorithms and makes them interchangeable
• Command Pattern: Encapsulates a request as an object
• State Pattern: Allows an object to alter its behavior when its internal state changes
• Template Method Pattern: Defines the skeleton of an algorithm in a method

Deep Dive: Key Design Patterns

The Singleton Pattern

The Singleton pattern ensures that a class has only one instance and provides a global point of access to it. This is useful when exactly one object is needed to coordinate actions across the system.

When to Use:

• When you need exactly one instance of a class (database connections, logging, configuration)
• When you need global access to that instance
• When the instance should be lazy-initialized

Example Implementation:

class Database {
  private static instance: Database | null = null;
  
  private constructor() {
    // Private constructor prevents direct instantiation
  }
  
  public static getInstance(): Database {
    if (!Database.instance) {
      Database.instance = new Database();
    }
    return Database.instance;
  }
  
  public query(sql: string): void {
    console.log(`Executing: ${sql}`);
  }
}

// Usage
const db1 = Database.getInstance();
const db2 = Database.getInstance();
console.log(db1 === db2); // true - same instance

Considerations: While Singleton is useful, it can make testing difficult and can hide dependencies. Use it judiciously.

The Factory Pattern

The Factory pattern provides an interface for creating objects without specifying their exact classes. It encapsulates object creation and provides flexibility in deciding which class to instantiate.

When to Use:

• When you don’t know beforehand the exact types of objects your code will work with
• When you want to provide a library of products and expose only their interfaces
• When you want to extend your code to work with new types without modifying existing code

Example Implementation:

interface Animal {
  makeSound(): void;
}

class Dog implements Animal {
  makeSound(): void {
    console.log('Woof!');
  }
}

class Cat implements Animal {
  makeSound(): void {
    console.log('Meow!');
  }
}

class AnimalFactory {
  static createAnimal(type: string): Animal {
    switch (type) {
      case 'dog':
        return new Dog();
      case 'cat':
        return new Cat();
      default:
        throw new Error(`Unknown animal type: ${type}`);
    }
  }
}

// Usage
const dog = AnimalFactory.createAnimal('dog');
dog.makeSound(); // Woof!

The Observer Pattern

The Observer pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.

When to Use:

• When changes to one object require changing other objects, and you don’t know how many objects need to be changed
• When an object should notify other objects without making assumptions about who those objects are
• In event-driven systems, MVC architectures, and reactive programming

Example Implementation:

interface Observer {
  update(data: any): void;
}

class Subject {
  private observers: Observer[] = [];
  
  attach(observer: Observer): void {
    this.observers.push(observer);
  }
  
  notify(data: any): void {
    this.observers.forEach(observer => observer.update(data));
  }
}

class EmailObserver implements Observer {
  update(data: any): void {
    console.log(`Email sent: ${data}`);
  }
}

// Usage
const subject = new Subject();
subject.attach(new EmailObserver());
subject.notify('Order placed');

The Strategy Pattern

The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It lets the algorithm vary independently from clients that use it.

When to Use:

• When you have multiple ways to perform a task
• When you want to avoid exposing complex, algorithm-specific data structures
• When you want to switch algorithms at runtime

Example Implementation:

interface PaymentStrategy {
  pay(amount: number): void;
}

class CreditCardPayment implements PaymentStrategy {
  pay(amount: number): void {
    console.log(`Paid ${amount} using Credit Card`);
  }
}

class PayPalPayment implements PaymentStrategy {
  pay(amount: number): void {
    console.log(`Paid ${amount} using PayPal`);
  }
}

class PaymentProcessor {
  private strategy: PaymentStrategy;
  
  constructor(strategy: PaymentStrategy) {
    this.strategy = strategy;
  }
  
  setStrategy(strategy: PaymentStrategy): void {
    this.strategy = strategy;
  }
  
  processPayment(amount: number): void {
    this.strategy.pay(amount);
  }
}

// Usage
const processor = new PaymentProcessor(new CreditCardPayment());
processor.processPayment(100);
processor.setStrategy(new PayPalPayment());
processor.processPayment(200);

Design Patterns in Modern Development

Many modern frameworks and libraries implement design patterns under the hood. Understanding these patterns helps you:

• React: Uses Observer pattern for state management, Factory pattern for component creation
• Express.js: Uses Middleware pattern (a variant of Chain of Responsibility)
• Redux: Implements Observer pattern for state subscriptions
• Node.js EventEmitter: Classic implementation of Observer pattern

Common Pitfalls and Best Practices

Pitfalls to Avoid:

• Over-engineering: Don’t use patterns where simple code would suffice
• Pattern obsession: Not every problem needs a design pattern
• Misapplication: Using the wrong pattern for a problem
• Complexity: Some patterns add complexity—ensure the benefit outweighs the cost

Best Practices:

• Start Simple: Begin with straightforward code, refactor to patterns when needed
• Understand the Problem: Make sure you understand the problem before applying a pattern
• Know Your Patterns: Study the Gang of Four patterns and modern variations
• Practice: Implement patterns in your projects to gain experience
• Read Code: Study how popular frameworks use patterns

Learning Path for Design Patterns

1. Start with the Basics: Understand Singleton, Factory, and Observer patterns
2. Study Real Examples: Look at how patterns are used in popular frameworks
3. Practice Implementation: Build small projects using different patterns
4. Read the Gang of Four: Study the original “Design Patterns” book
5. Explore Modern Patterns: Learn about patterns specific to your technology stack

Conclusion

Design patterns are powerful tools in a developer’s arsenal, but they’re not silver bullets. They provide proven solutions to common problems and create a shared vocabulary for developers. However, the key is understanding when and how to apply them appropriately.

Remember: patterns should serve your code, not the other way around. Start with clear, simple code, and introduce patterns when they genuinely solve a problem or improve maintainability. As you gain experience, you’ll develop an intuition for when patterns are appropriate and when they’re overkill.

The journey to mastering design patterns is ongoing. Each pattern you learn adds another tool to your toolkit, making you a more versatile and effective developer. Keep practicing, keep learning, and most importantly, keep building.

From the blog BforBuild by BforBuild and used with permission of the author. All other rights reserved by the author.

Hello everyone, my name is Rick Djouwe, and this semester I am beginning CS 343: Software Construction, Design & Architecture. I am truly excited for this class because it represents the next step in strengthening my ability to think beyond coding and focus on building well-structured, scalable, and maintainable software systems.

What This Course is About

CS 343 covers a wide range of essential topics in modern software development, including:

• Design principles such as abstraction, encapsulation, inheritance, and polymorphism.
• Best practices like SOLID, DRY (“Don’t Repeat Yourself”), and YAGNI (“You Ain’t Gonna Need It”).
• Design patterns that provide reusable solutions to common problems.
• Software architectures and frameworks, including REST API design.
• Refactoring, code smells, and concurrency, which improve software quality and longevity.
• Modeling and documentation tools like UML, which ensure clear communication of design decisions.

In short, this course is not just about writing code, it’s about learning to think like a software engineer who can approach problems critically, design solutions thoughtfully, and work effectively with others.

Skills and Outcomes

Through CS 343, I will gain valuable experience in:

• Collaborating with stakeholders to design, test, and deliver software systems.
• Applying professional judgment and staying current with evolving tools and practices.
• Organizing projects using proven methodologies and team processes.
• Communicating complex technical concepts clearly, both in writing and orally.

These outcomes connect directly to the broader goals of my Computer Science major: analyzing problems, building solutions, and developing the professional skills needed to succeed in the field.

Why This Matters to Me

As someone pursuing a career as a software engineer specializing in artificial intelligence, this course will help me strengthen the foundations of software design and architecture that are critical in building intelligent, scalable systems. Beyond my academic goals, I also see a strong connection to my current role as an Automation Developer at The Hanover Insurance Group, where I contribute to projects that rely on thoughtful design, testing, and collaboration. The principles and practices I learn here will make me more effective in my work today while preparing me for even greater responsibilities in the future.

I am eager to reflect on my progress throughout the semester, connect this material with experiences across my other courses, and apply these lessons directly to both my professional role and long-term career.

For me, CS 343 is more than a class, it’s a bridge between where I am now and the kind of innovative, responsible, and skilled software engineer I strive to become. I am also excited to meet everyone in this course and learn from each other as we move forward together. Feel free to reach out if you’d like to connect, collaborate, or study together this semester!

From the blog Rick’s Software Journal by RickDjouwe1 and used with permission of the author. All other rights reserved by the author.

This week, I looked into the topic of something called microservice architecture. It’s a way of designing software systems that breaks them into smaller, independent services that work together. To better understand it, I read the article “MicroserviceArchitecture”, which gave me a beginner-friendly explanation of how it works, its benefits, and some challenges. Since I’m new to computer science, I thought this topic was interesting because it seems like something I might use if I ever work on big software projects.

The article explains that instead of building one big application (a monolith), microservices split the application into smaller pieces. Each piece, or “service,” can do a specific job, like managing user accounts or processing payments. These services talk to each other using APIs, and they’re independent, so you can change or fix one without messing up the others. The article also talks about the pros and cons. On the good side, microservices make apps easier to scale and maintain. But on the downside, they can get pretty complicated to set up and manage.

I picked this article because microservices came up during class discussions, and I didn’t really get it at first. I wanted to find a resource that explained the basics without assuming too much prior knowledge. This article seemed perfect for a beginner because it explains things step by step. I also chose it because I’ve always wondered how big companies like Netflix or Amazon manage their systems, and it turns out they use microservices.

The biggest thing I learned is how microservices make scaling easier. For example, if one part of an app is getting more traffic—like a checkout service for an online store—you can scale just that service without touching the rest of the app. I thought that was really cool because it makes so much sense for big companies. Another thing I learned is how microservices make it easier for teams to work on different parts of a project at the same time. On the flip side, I also realized that microservices can be tricky because you have to make sure all the services work together smoothly. This made me think about how important it is to plan ahead when designing software.

I think this knowledge will be useful later when I work on group projects. If we ever build something complex, I might suggest using microservices to keep things organized. I also want to learn more about tools like Docker, which the article mentioned, because they help manage microservices.

Resource:

microservices-architecture

From the blog Computer Science From a Basketball Fan by Brandon Njuguna and used with permission of the author. All other rights reserved by the author.