Software Design Patterns

List of All Software Design Patterns

Software design patterns are categorized into three main types based on their primary function: Creational, Structural, and Behavioral patterns. Each design pattern provides a generalized solution to common software design problems. Below is a comprehensive list of design patterns with a brief description for each category.

1. Creational Design Patterns

Creational patterns are concerned with the process of object creation, making it more flexible and efficient.

  1. Singleton Pattern
  • Ensures a class has only one instance and provides a global point of access to it.
  • Use case: Managing shared resources like logging, database connections, etc.
  1. Factory Method Pattern
  • Defines an interface for creating an object, but allows subclasses to alter the type of objects that will be created.
  • Use case: When the exact type of object to create is not known until runtime.
  1. Abstract Factory Pattern
  • Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
  • Use case: When a system needs to create multiple families of related objects.
  1. Builder Pattern
  • Separates the construction of a complex object from its representation, allowing the same construction process to create different representations.
  • Use case: When an object needs to be created with many optional components.
  1. Prototype Pattern
  • Allows creating new objects by copying an existing object, known as the prototype.
  • Use case: When creating an object is costly or complex and cloning an existing object is more efficient.

2. Structural Design Patterns

Structural patterns deal with the composition of classes or objects and how they can be structured to form larger systems.

  1. Adapter Pattern
  • Converts the interface of a class into another interface that the client expects.
  • Use case: Integrating two incompatible interfaces.
  1. Bridge Pattern
  • Decouples an abstraction from its implementation so that the two can vary independently.
  • Use case: When you want to separate abstraction and implementation.
  1. Composite Pattern
  • Composes objects into tree-like structures to represent part-whole hierarchies.
  • Use case: When you need to represent hierarchies of objects, like files and directories.
  1. Decorator Pattern
  • Attaches additional responsibilities to an object dynamically.
  • Use case: When you want to add features to individual objects without altering the structure.
  1. Facade Pattern
  • Provides a simplified interface to a complex subsystem.
  • Use case: When you want to provide a simpler interface to a system with many classes.
  1. Flyweight Pattern
  • Reduces the memory usage by sharing common data among similar objects.
  • Use case: When a large number of objects are needed, but many of them share the same state.
  1. Proxy Pattern
  • Provides a surrogate or placeholder object to control access to another object.
  • Use case: When access control or lazy initialization is needed.

3. Behavioral Design Patterns

Behavioral patterns focus on improving or simplifying the communication between objects, their responsibilities, and how they interact.

  1. Chain of Responsibility Pattern
  • Allows a request to be passed along a chain of handlers. Each handler either processes the request or passes it on to the next handler.
  • Use case: When multiple objects can handle a request, and the handler is unknown until runtime.
  1. Command Pattern
  • Encapsulates a request as an object, thereby allowing parameterization of clients with queues, requests, and operations.
  • Use case: When you want to decouple sender and receiver of a request.
  1. Interpreter Pattern
  • Defines a representation for a language’s grammar and an interpreter to interpret the sentences in the language.
  • Use case: When you need to evaluate expressions or interpret languages (e.g., SQL query parsing).
  1. Iterator Pattern
  • Provides a way to access elements of an aggregate object sequentially without exposing its underlying representation.
  • Use case: When you need to traverse a collection of objects without exposing the internal structure.
  1. Mediator Pattern
  • Defines an object that encapsulates how a set of objects interact. Promotes loose coupling by keeping objects from referring to each other explicitly.
  • Use case: When you have many-to-many relationships between objects and want to centralize communication.
  1. Memento Pattern
  • Captures and externalizes an object’s internal state so that it can be restored later without violating encapsulation.
  • Use case: When you need to save the state of an object to undo/redo actions.
  1. Observer Pattern
  • Defines a one-to-many dependency between objects, so when one object changes state, all its dependents are notified.
  • Use case: When one object’s state change needs to notify others, like in event-driven systems.
  1. State Pattern
  • Allows an object to alter its behavior when its internal state changes, appearing as if it changed its class.
  • Use case: When an object needs to change behavior based on its state, like in a finite state machine.
  1. Strategy Pattern
  • Defines a family of algorithms, encapsulates each one, and makes them interchangeable.
  • Use case: When you want to choose an algorithm at runtime, like sorting strategies.
  1. Template Method Pattern
  • Defines the skeleton of an algorithm in a method, deferring some steps to subclasses.
  • Use case: When you have a general algorithm but want to allow customization in specific steps.
  1. Visitor Pattern
  • Allows you to define new operations on elements of an object structure without changing the classes of the elements.
  • Use case: When you want to add new functionality to an object structure without altering its classes.

4. Concurrency Design Patterns

Concurrency patterns deal with multi-threading and parallelism, allowing for better resource management and synchronization.

  1. Active Object Pattern
  • Decouples method execution from method invocation to ensure that a method can be executed asynchronously.
  • Use case: When you need to decouple task execution from the thread initiating the request.
  1. Future Pattern
  • Represents a result that will eventually be available, allowing the caller to continue executing other tasks while waiting for the result.
  • Use case: When you want to fetch a result asynchronously without blocking the caller.
  1. Thread Pool Pattern
  • Manages a pool of worker threads that can be reused to perform a number of tasks concurrently.
  • Use case: When you have multiple tasks to execute concurrently, and you want to minimize the cost of creating new threads.
  1. Reactor Pattern
  • An event-driven pattern that provides a mechanism for handling multiple I/O operations asynchronously.
  • Use case: When handling multiple input/output operations concurrently in non-blocking I/O systems.

5. Architectural Design Patterns

These are larger-scale patterns used to shape the overall structure of the system, often integrating several design patterns.

  1. Model-View-Controller (MVC)
  • Separates the application into three interconnected components: Model, View, and Controller.
  • Use case: When building user interfaces where you want to separate logic from display.
  1. Model-View-ViewModel (MVVM)
  • Similar to MVC, but with an additional ViewModel component to bind data between the View and Model.
  • Use case: When building complex user interfaces (often used in desktop applications).
  1. Client-Server Pattern
  • A distributed architecture pattern where one or more client devices communicate with a central server.
  • Use case: Common in networked applications where clients and servers interact via a request-response mechanism.
  1. Layered Pattern
  • Divides an application into layers (presentation, business logic, data access) to organize responsibilities.
  • Use case: When building applications with multiple levels of functionality.
  1. Microservices Pattern
  • Structures an application as a set of loosely coupled services that can be independently developed, deployed, and scaled.
  • Use case: When building large, scalable, and maintainable systems using a distributed architecture.
  1. Event-Driven Architecture
  • Systems are designed around the production, detection, and reaction to events.
  • Use case: In systems where many components must react to state changes or events asynchronously.

Conclusion

The design patterns listed above are fundamental solutions to common software design problems. Understanding when and how to apply these patterns can drastically improve the quality, maintainability, and scalability of your software projects. By familiarizing yourself with these patterns, you can select the right pattern for each situation and avoid reinventing the wheel.

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