A design pattern is a reusable solution to a commonly occurring problem in software design. They are not finished, ready-to-use pieces of code but rather templates or blueprints that can be adapted for a specific situation. Developers use these formalized best practices to write more structured, efficient, and maintainable code.

Analogy: A cooking recipe

• A recipe for making a cake isn’t the final cake itself; it’s a guide to creating one.
• The recipe lists the ingredients (objects and classes) and describes the steps to follow to achieve a desired outcome (a well-designed piece of software).
• Just as you can adapt a recipe for different tastes, a developer can customize a design pattern to fit the specific needs of their project.

Why design patterns are important

• Encapsulate best practices: They represent tried-and-tested solutions that have evolved through the collective experience of many developers.
• Improve communication: Patterns create a standard vocabulary for developers to discuss complex concepts. Instead of explaining a detailed approach, a developer can simply say, “We’ll use the Singleton pattern,” and the team will understand the overall structure.
• Speed up development: By providing a proven starting point, patterns save developers from having to reinvent the wheel every time they encounter a similar problem.
• Enhance code quality: Utilizing design patterns results in code that is more flexible, reusable, and easier to maintain, particularly as a project evolves.
• Prevent subtle issues: Experienced developers know the potential pitfalls of certain coding approaches. Patterns help prevent these issues by guiding you toward more robust solutions. 

Categories of design patterns

Design patterns are most famously categorized by the “Gang of Four” book, Design Patterns: Elements of Reusable Object-Oriented Software, into three main groups based on their purpose: 

• Creational patterns: Deal with object creation in a flexible way.
• Structural patterns: Concern how classes and objects are composed to form larger, more complex structures.
• Behavioral patterns: Focus on how objects communicate and assign responsibilities. 

Creational patterns

These patterns are all about creating objects flexibly and efficiently. Instead of simply using a new command, they hide the logic of creating objects, which gives you more control and flexibility. 

Analogy: A food-truck service

• If you wanted a burrito, you wouldn’t need to know how the server prepares all the individual ingredients.
• You just ask for a “burrito,” and the food truck’s system (the pattern) handles all the steps of assembling it for you. 

Structural patterns

These patterns focus on how classes and objects are put together to form larger, more complex structures. They help ensure that a change to one part of the system doesn’t require a change to the entire system. 

Analogy: The parts of a computer

• Your computer is made up of many different parts—like the hard drive, monitor, and keyboard—that need to work together.
• An adapter pattern, for example, is like a USB port that allows many different devices to “plug in” and work with your computer, even if they were made by different companies. 

Behavioral patterns

These patterns are concerned with how objects communicate and interact with each other. They help you manage complex processes and responsibilities by defining clear and organized communication between different parts of the system. 

Analogy: The workflow at a restaurant

• When a customer’s order comes in, it doesn’t go directly to every single kitchen employee.
• Instead, the order is passed along a “chain of responsibility.” The server takes it, the line cook prepares it, and the runner delivers it. Each person in the chain handles their specific task without having to know about all the other steps.

Did this post help you better understand the concept? Let me know your thoughts in the comments below! Don’t forget to follow us on Instagram @coderz.py for more OODP tips and solutions to ace your coding interviews.