Design Patterns
A Design Pattern is a set of repeatedly verified reusable solutions used to solve common problems in software design.
Simply put, a design pattern is acode-writing pattern。
Design patterns are not specific code, but rather tell you what structure to use to organize code in certain situations, making the system more flexible and easier to maintain.
The Essence of Design Patterns
Imagine blueprints in the construction industry: architects don't design houses from scratch every time, but instead refer to proven architectural patterns. Similarly, in software development, design patterns provide us with proven "software blueprints," helping us avoid reinventing the wheel.
Why Do We Need Design Patterns
1. Higher Maintainability
- Design patterns make code easier to modify.
- When requirements change, you only need to modify specific modules rather than making large-scale global changes.
2. Strong Reusability
Abstract design allows you to reuse the same structure across multiple projects.
3. Team Collaboration Language
"Implement this feature using the Decorator pattern" — team members immediately understand the intent, saving communication costs.
4. Improve Architectural Thinking
Learning design patterns is not about memorizing code, but about learning how to abstract problems and how to design extension points.
Classification of Design Patterns
Design patterns are usually divided into three major categories, each solving design problems at a different level:
Creational Patterns
These patterns focus on the object creation mechanism, making object creation more flexible and aligned with requirements.
The main patterns include:
- Singleton Pattern: ensures a class has only one instance
- Factory Pattern: provides an interface for creating objects, letting subclasses decide which class to instantiate
- Builder Pattern: separates the construction of a complex object from its representation
Structural Patterns
These patterns focus on how classes and objects are composed to form larger structures.
The main patterns include:
- Adapter Pattern: enables incompatible interfaces to work together
- Decorator Pattern: dynamically adds new functionality to objects
- Proxy Pattern: provides a proxy for another object to control access to it
Behavioral Patterns
These patterns focus on responsibility distribution and communication between objects.
The main patterns include:
- Observer Pattern: defines a one-to-many dependency relationship between objects
- Strategy Pattern: defines a family of algorithms that can be substituted for each other
- Command Pattern: encapsulates requests as objects
Common Design Pattern Application Scenarios
Let's quickly understand the application scenarios of several common design patterns through a table:
| Design Pattern | Problem Solved | Typical Application Scenarios |
|---|---|---|
| Singleton Pattern | Ensure a globally unique instance | Database connections, configuration management, logging systems |
| Factory Pattern | Complex object creation logic | Create different types of objects based on different conditions |
| Observer Pattern | Dynamic notification between objects | Event handling systems, message subscription |
| Decorator Pattern | Dynamically extend functionality | IO stream processing, middleware chains |