What are software design patterns

Software design patterns are general, reusable solutions to common problems that occur during software design and development. They represent best practices and proven solutions to specific design problems and help developers create more maintainable, flexible, and scalable software systems. Design patterns are not actual pieces of code but rather templates or blueprints that can be applied to different situations.

Key parts of software design patterns:

• Reusability: Design patterns promote reusability by providing tested and proven solutions to common problems. Instead of starting from scratch, developers can use these patterns to solve recurring design issues.

• Abstraction: Abstract the complexities of a problem, making it easier for developers to understand and communicate about design concepts. They provide a common vocabulary for discussing design decisions.

• Flexibility: By using design patterns, software systems become more flexible and adaptable to changes. Patterns help in creating designs that are easy to modify and extend without causing major disruptions to the existing code.

• Scalability: Design patterns contribute to scalable software architectures by providing guidelines on how to structure and organize code. This makes it easier to scale a system by adding new features or components.

• Maintainability: Patterns improve the maintainability of code by promoting a modular and organized structure. Changes or updates to one part of the system are less likely to affect other parts, reducing the risk of introducing bugs.

Some common categories of design patterns include:

• Creational Patterns: Concerned with the process of object creation.
  • Examples: Singleton, Factory Method, Abstract Factory, Builder, Prototype.

• Structural Patterns: Focus on the composition of classes or objects.
  • Examples: Adapter, Bridge, Composite, Decorator, Facade, Proxy.

• Behavioral Patterns: Deal with the interaction and communication between objects.
  • Examples: Observer, Strategy, Command, State, Template Method, Visitor.

Understanding and applying design patterns can significantly improve the quality and maintainability of software. You need to use them judiciously and not apply them blindly, as each pattern has its own strengths and weaknesses, and their suitability depends on the specific context and requirements of a given project.

Categories of design patterns

• Creational Patterns:
  • These patterns are focused on the process of object creation. They provide mechanisms for creating instances of classes or objects in a way that is flexible, efficient, and decoupled from the system.
  • Examples include:
    • Singleton Pattern: Ensures a class has only one instance and provides a global point of access to it.
    • Factory Method Pattern: Defines an interface for creating an object but leaves the choice of its type to the subclasses, creating instances without specifying the exact class.
    • 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, known as the prototype.

• Structural Patterns:
  • These patterns deal with the composition of classes or objects, focusing on how classes and objects are organized to form larger structures.
  • Examples include:
    • Adapter Pattern: Allows the interface of an existing class to be used as another interface.
    • Bridge Pattern: Separates an abstraction from its implementation so that both can vary independently.
    • Composite Pattern: Composes objects into tree structures to represent part-whole hierarchies.
    • Decorator Pattern: Attaches additional responsibilities to an object dynamically.
    • Facade Pattern: Provides a simplified interface to a set of interfaces in a subsystem.
    • Proxy Pattern: Controls access to an object by acting as a surrogate or placeholder.

• Behavioral Patterns:
  • These patterns focus on the interaction and communication between objects, defining how they collaborate and share responsibility.
  • Examples 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 algorithm, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
    • Command Pattern: Encapsulates a request as an object, thereby allowing for parameterization of clients with different requests, queuing of requests, and logging of the requests.
    • State Pattern: Allows an object to alter its behavior when its internal state changes, the object appears to change its class.
    • Template Method Pattern: Defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.
    • Visitor Pattern: Represents an operation to be performed on the elements of an object structure, and allows the definition of new operations without changing the classes of the elements.