Design Patterns
Design patterns are general solutions to common problems that frequently occur in software design and development. They serve as blueprints or templates that guide developers in structuring code to achieve specific goals and improve software design. There are 23 well-known design patterns, which are categorized into three groups: Creational, Structural, and Behavioral patterns.
Table of Contents
Creational Design Patterns:
Creational design patterns focus on object creation mechanisms, providing flexible ways to create objects without exposing the creation logic. They hide the complexity of object instantiation and ensure that a class has only one instance or that a family of related objects is created together.
- Singleton Pattern: Ensures a class has only one instance and provides a global point of access to that instance.
- Factory Method Pattern: Provides 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 a complex object from its representation, allowing the same construction process to create different representations.
- Prototype Pattern: Creates new objects by copying an existing object, thereby avoiding the need for costly instantiation.
Structural Design Patterns:
Structural design patterns deal with class and object composition, defining how objects are connected and forming larger structures. They focus on ensuring that classes and objects work together effectively to provide new functionalities.
- Adapter Pattern: Allows incompatible interfaces to work together by providing a wrapper that converts one interface into another.
- Bridge Pattern: Separates an object’s abstraction from its implementation, allowing them to vary independently.
- Composite Pattern: Composes objects into tree-like structures to represent part-whole hierarchies, allowing clients to treat individual objects and compositions uniformly.
- Decorator Pattern: Dynamically adds new behavior to objects without modifying their code, providing a flexible alternative to subclassing.
- Facade Pattern: Provides a unified interface to a set of interfaces in a subsystem, simplifying complex systems and reducing dependencies.
- Flyweight Pattern: Shares objects to reduce memory usage when many similar objects are needed.
Behavioral Design Patterns:
Behavioral design patterns focus on how objects interact and communicate with each other, managing the flow of control and responsibilities in an application.
- Chain of Responsibility Pattern: Passes a request along a chain of handlers until one of them handles the request.
- Command Pattern: Encapsulates a request as an object, allowing parameterization of clients with different requests, queuing of requests, and logging of their execution.
- Interpreter Pattern: Provides a way to evaluate language grammar or expressions, often used for interpreting DSLs (Domain-Specific Languages).
- Iterator Pattern: Provides a way to access elements of a collection sequentially without exposing its underlying representation.
- Mediator Pattern: Defines an object that encapsulates communication between objects in a system, reducing their direct interactions and dependencies.
- Memento Pattern: Allows an object’s state to be captured and restored later without exposing its internal structure.
- Observer Pattern: Defines a one-to-many dependency between objects, so when one object changes state, its dependents (observers) are notified and updated automatically.
- State Pattern: Allows an object to change its behavior when its internal state changes, encapsulating state-specific logic in separate classes.
- Strategy Pattern: Defines a family of algorithms and makes them interchangeable, allowing clients to choose the algorithm they need.
- Template Method Pattern: Defines the structure of an algorithm in a method but allows its subclasses to override certain steps of the algorithm.
- Visitor Pattern: Lets you add further operations to objects without having to modify them by separating the operations into visitor objects.
Design patterns are essential tools for software developers, providing proven solutions to common design problems. They promote code reusability, maintainability, and scalability by encouraging a structured and standardized approach to software design. By understanding and applying design patterns correctly, developers can write more robust and flexible code, leading to better software development practices.