Design Patterns
A Design Pattern is a set of repeatedly verified, reusable solutions used to solve common problems in software design.
In simple terms, a design pattern is acoding convention/approach。
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 major changes globally.
2. Strong Reusability
Abstract design allows you to reuse the same structures across multiple projects.
3. Team Collaboration Language
"Implement this feature using the decorator pattern" — team members immediately understand the intent, saving communication costs.
4. Improved 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 different levels:
Creational Patterns
These patterns focus on object creation mechanisms, making object creation more flexible and better suited to requirements.
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 the composition of classes and objects to form larger structures.
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 other objects to control access to that object
Behavioral Patterns
These patterns focus on the allocation of responsibilities and communication between objects.
Main patterns include:
- Observer Pattern: Defines a one-to-many dependency relationship between objects
- Strategy Pattern: Defines a family of algorithms, making them interchangeable
- 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 Scenario |
|---|---|---|
| Singleton Pattern | Ensures a globally unique instance | Database connections, configuration management, logging systems |
| Factory Pattern | Complex object creation logic | Creating different types of objects based on different conditions |
| Observer Pattern | Dynamic notification between objects | Event handling systems, message subscription |
| Decorator Pattern | Dynamically extending functionality | IO stream processing, middleware chains |