Design Patterns Classification

Design Patterns Classification

Design patterns are mature solutions to common problems in software development. Based on their scope of influence, they can be categorized into three major classes: Creational Patterns, Structural Patterns, and Behavioral Patterns. These patterns focus respectively on object creation, structural organization, and behavioral interaction, serving as the core foundation for software architecture design.
Creational patterns concern the process of object creation, aiming to abstract creation logic to enhance code flexibility and maintainability.
1. Singleton Pattern
Ensures that a class has only one instance and provides a unified access interface. It is suitable for scenarios requiring global state management, such as database connection pools.
2. Factory Pattern
Encapsulates object creation logic within factory classes to decouple clients from implementation details. For example, calling new CarFactory().createVehicle() avoids direct instantiation of objects.
3. Builder Pattern
Constructs an object step-by-step, supporting flexible configuration. It is suitable for creating complex objects, such as building a complex GUI interface.

Structural Patterns

Structural patterns concern the interaction and organization methods between objects, achieving functional extension through composition rather than inheritance.
1. Adapter Pattern
Integrates classes with incompatible interfaces to achieve unified interfaces. For example, adapting an old API to fit the interface of a new framework.
2. Decorator Pattern
Dynamically adds functionality to objects; for instance, adding watermarking or encryption features to PDF documents without modifying the original code.
3. Proxy Pattern
Controls access to real objects through proxy objects to implement permission control or logging. For example, using a proxy pattern to add transaction management to database access operations.

Behavioral Patterns

Behavioral patterns concern behavioral control and responsibility allocation between objects, improving code flexibility by encapsulating interaction logic.
1. Observer Pattern
Implements a one-to-many dependency relationship; for instance, the subscription mechanism in news client applications.
2. Strategy Pattern
Defines a family of algorithms, encloses them within classes to facilitate algorithm replacement and extension. For example, adjusting payment methods (credit card/cash) based on exchange rates.
3. State Pattern
Encapsulates object states to enable dynamic switching of behavior; for instance, an e-commerce system switching recommendation algorithms according to user levels.

The classification of design patterns is not fixed; in practical applications, the choice should be flexible based on specific scenarios. For example, the Singleton pattern is suitable for resource-constrained environments, while the Strategy pattern fits business logic requiring dynamic algorithm switching. Understanding pattern classifications aids in building software systems with high cohesion and low coupling.