Top 10 Software Design Principles Every Developer Should Know

Introduction:

Introduce the importance of foundational software design principles. Explain that these principles help ensure that software remains maintainable, scalable, and user-friendly, even as it grows in complexity. Acknowledge the challenges developers face when managing complex codebases and explain how these principles are timeless guidelines for overcoming those challenges.

[1] KISS (Keep It Simple, Stupid)

- Explanation: KISS encourages simplicity. Complex code is difficult to maintain, understand, and extend.

- Key Takeaways:

- Write clear and concise code.

- Avoid over-engineering and unnecessary complexity.

- Example: Instead of writing a highly complex, nested function, aim for simpler, modular functions that each accomplish a specific task. For instance, if writing a search function, keep it focused on searching rather than handling unrelated tasks.

[2] DRY (Don’t Repeat Yourself)

- Explanation: DRY is all about avoiding redundancy by abstracting out repeated code into reusable components.

- Key Takeaways:

- Use functions, classes, and variables to store commonly used logic or values.

- Prevent code duplication to ease maintenance.

- Example: If you have a calculation that appears in multiple places, create a function for it instead of repeating the calculation throughout the codebase.

[3] YAGNI (You Ain't Gonna Need It)

- Explanation: YAGNI advises against coding features you don't currently need. Adding unnecessary features adds complexity and often leads to code bloat.

- Key Takeaways:

- Implement only what is essential.

- Avoid adding features based on potential future needs.

- Example: Instead of adding multiple sorting options to a search feature because "they might be useful later," start with just the basics. Add more options if and when they are required.

[4] SOLID Principles

Single Responsibility Principle (SRP)

- Explanation: A class should have only one reason to change, i.e., one responsibility.

- Example: In an e-commerce application, a Product class should only handle product-related properties, not ordering or payment.

Open/Closed Principle (OCP)

- Explanation: Code should be open for extension but closed for modification.

- Example: Instead of modifying a class to add new functionality, use inheritance or interfaces to extend behavior.

Liskov Substitution Principle (LSP)

- Explanation: Subtypes should be substitutable for their base types without breaking functionality.

- Example: If a Rectangle class is used in place of a Shape class, the behavior should still meet the Shape expectations.

Interface Segregation Principle (ISP)

- Explanation: Clients should not be forced to depend on methods they do not use.

- Example: Instead of having a single interface with many unrelated methods, break it down into smaller, specific interfaces.

Dependency Inversion Principle (DIP)

- Explanation: High-level modules should not depend on low-level modules. Both should depend on abstractions.

- Example: Instead of a Payment class directly calling CreditCardPayment or PayPalPayment, use a PaymentProcessor interface that these specific classes can implement.

[5] Principle of Least Astonishment (or Surprise)

- Explanation: Design software in a way that aligns with user expectations. When the software behaves predictably, it reduces user frustration and enhances user experience.

- Key Takeaways:

- Use familiar patterns and terminology.

- Avoid unexpected or hidden behavior.

- Example: In an app, a “Save” button should save without prompting unless it’s critical; adding unexpected prompts can disrupt user flow.

[6] Principle of Modularity

- Explanation: Break down software into self-contained modules. This makes the software easier to test, maintain, and extend.

- Key Takeaways:

- Each module should have a well-defined purpose.

- Modules should be designed to work independently.

- Example: In a web application, keep the authentication, user profile, and payment features as separate modules.

[7] Principle of Abstraction

- Explanation: Hide the internal workings of a module or system behind a simple interface.

- Key Takeaways:

- Focus on what the code does, not how it does it.

- Simplify complex systems for the user.

- Example: Instead of exposing the details of a complex payment system, provide a processPayment() method that abstracts away the implementation.

[8] Principle of Encapsulation

- Explanation: Limit access to the internal state of an object. This helps in managing how data flows and is modified within the software.

- Key Takeaways:

- Use private fields and public methods to control access.

- Increase maintainability and reduce unintended side effects.

- Example: In a User class, make sensitive data like password private, accessible only through specific methods.

[9] Principle of Least Knowledge (Law of Demeter)

- Explanation: A module or class should not "know" more than it needs to about other parts of the system.

- Key Takeaways:

- Encourage independence between modules.

- Reduce interdependencies to avoid ripple effects.

- Example: Instead of a function calling multiple methods across various classes, it should interact only with closely related classes.

[10] Principle of Low Coupling & High Cohesion

- Low Coupling: Ensure components or modules are as independent as possible.

- High Cohesion: Ensure that each module has a single, well-defined purpose.

- Key Takeaways:

- Low coupling promotes easier modification.

- High cohesion makes modules more understandable and testable.

- Example: In a UserProfile module, only user-related functions should exist (high cohesion), and it should have minimal dependencies on other modules (low coupling).

Personal Insight Examples

1. KISS: “I’ve seen how teams can get caught up in creating overly complex solutions. A simple data retrieval service I worked on became much easier to maintain when we stripped it down to just handle core database interactions. Simplifying it also helped the new team members onboard faster.”
2. DRY: “Early in my career, I worked on a project with scattered calculations across multiple files. Any small change meant finding and updating each instance—a nightmare. Consolidating them into a reusable function saved us countless hours and improved our accuracy. I always emphasize DRY now!”
3. YAGNI: “During a recent project, we were tempted to add some ‘nice-to-have’ features. In hindsight, avoiding these extras saved us time and kept the project on track. My advice is to stick to the essentials first; you can always add more later if necessary.”
4. SOLID: "In a microservices architecture project, we applied SOLID principles to ensure each service had a single responsibility and used dependency injection to manage interactions. This approach drastically reduced our testing and debugging time."
5. Principle of Least Surprise: "I worked on a dashboard feature where users were frustrated because the 'Save' button asked for confirmation every time, which they found unnecessary. Simplifying it to save automatically when changes are detected and aligned with user expectations improves their experience.”
6. Modularity: “I learned the value of modularity when collaborating on a healthcare app where we kept separate features like scheduling, billing, and patient records. This made it easier to test and allowed other teams to work on specific modules independently, speeding up development.”
7. Encapsulation: "I once led a team refactoring project where we encapsulated sensitive data into private variables. This improved security and reduced the risk of unintended data modifications, enhancing our overall data integrity.”
8. Least Knowledge: “One of my projects involved reducing dependencies between modules. By designing the components to communicate only when necessary, we made updates far less error-prone. This is now a guiding principle in my architecture designs.”
9. Low Coupling & High Cohesion: "I worked on a finance system where we divided functionality into modules like reporting, transaction processing, and user management. Each module served a clear purpose, and minimal dependencies kept the codebase flexible and easy to expand.”

Conclusion:

These principles form the foundation of solid, sustainable software design. While it may not always be possible to follow every principle strictly, striving for them can lead to better code quality and easier maintenance. Encourage readers to incorporate these principles into their daily coding practices to enhance both their development process and final products.