Design patterns can be broadly categorized into three groups: creational, structural, and behavioral patterns. Each group serves a different purpose and addresses different aspects of software design.
1. Creational Patterns:
Creational patterns focus on object creation mechanisms, providing flexible ways to create objects without directly specifying their classes or constructors. These patterns enable decoupling of the client code from the concrete classes being instantiated, making the system more flexible and easier to maintain. Some common creational patterns include:
– Singleton Pattern: Ensures that only one instance of a class is created and provides a global point of access to it.
– Factory Pattern: Defines an interface for creating objects but allows subclasses to decide which class to instantiate.
– Abstract Factory Pattern: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
– Builder Pattern: Separates the construction of complex objects from their representation, allowing the same construction process to create different representations.
2. Structural Patterns:
Structural patterns deal with the composition of classes and objects to form larger structures and provide solutions for object composition without affecting the individual objects. These patterns help in defining relationships between classes and simplify the design by identifying simple ways of realizing relationships. Some common structural patterns include:
– Adapter Pattern: Converts the interface of a class into another interface that clients expect, allowing classes with incompatible interfaces to work together.
– Decorator Pattern: Allows adding new behaviors or responsibilities to objects dynamically without modifying their structure.
– Facade Pattern: Provides a simplified interface to a complex subsystem, making it easier to use and understand.
– Composite Pattern: Composes objects into tree structures to represent part-whole hierarchies, treating individual objects and compositions uniformly.
3. Behavioral Patterns:
Behavioral patterns focus on communication between objects, defining how they interact and distribute responsibilities. These patterns capture the interaction patterns between objects, making the system more flexible by providing loose coupling. Some common behavioral patterns include:
– Observer Pattern: Defines a one-to-many dependency between objects, so that when one object changes state, all its dependents are notified and updated automatically.
– Strategy Pattern: Defines a family of algorithms, encapsulates each one, and makes them interchangeable at runtime.
– Command Pattern: Encapsulates a request as an object, allowing parameterization of clients with different requests, queue or log requests, and support undoable operations.
– Template Method Pattern: Defines the skeleton of an algorithm in a base class, allowing subclasses to provide specific implementations of certain steps.
Creational patterns focus on object creation, structural patterns deal with object composition, and behavioral patterns address object interaction and communication. Each group of patterns provides solutions to different aspects of software design, contributing to modularity, flexibility, and reusability.