NARESH ASKANI

What are Design Patterns? Think of design patterns as pre-designed blueprints for solving common software design problems. They are reusable solutions to recurring design challenges. They are not concrete implementations but rather general guidelines that can be adapted to different scenarios.

Categorizing Design Patterns

Design patterns are typically categorized into three main groups:

1. Creational Patterns: These patterns deal with object creation mechanisms, trying to create objects in a flexible way.
2. Structural Patterns: These patterns deal with how classes and objects are composed to form larger structures.
3. Behavioral Patterns: These patterns are concerned with the interaction and communication between objects.

Creational Design Patterns

Creational patterns are concerned with how objects are created. They provide different ways to instantiate objects, making the creation process more flexible and independent of the system’s concrete classes.This allows for more flexibility and maintainability in the code.

Creational Patterns

Here are some of the most commonly used creational patterns:

• Factory Method: Defines an interface for creating an object, but lets subclasses decide which class to instantiate.
• Abstract Factory: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
• Builder: Separates the construction of a complex object from its representation, allowing the same construction process to create different representations.  
• Prototype: Creates new objects by copying an existing object.
• Singleton: Ensures a class has only one instance and provides a global point of access to it.

We’ll delve into each pattern in detail, providing code examples and explanations

Structural Patterns:

Structural Patterns deal with composition of classes and objects to form larger structures. They focus on relationships between objects and how they can be combined to create more complex systems.

• Adapter – Converts an interface into another interface that clients expect (e.g., power plug adapter).
• Decorator – Dynamically adds behaviors to objects without modifying their structure (e.g., adding features to a UI component).
• Proxy – Provides a placeholder or surrogate to control access to another object (e.g., lazy loading, security proxy).
• Bridge – Separates abstraction from implementation so they can evolve independently (e.g., different rendering APIs for UI components).
• Composite – Composes objects into tree structures to treat individual and composite objects uniformly (e.g., file system).
• Flyweight – Reduces memory usage by sharing common object states (e.g., caching character glyphs in text rendering).
• Facade – Provides a simplified interface to a complex subsystem (e.g., using a single API for multiple internal services).

Behavioral Patterns:

These patterns focus on how objects interact with each other and distribute responsibilities efficiently.

• Strategy – Defines a family of algorithms and makes them interchangeable (e.g., sorting strategies).
• Observer – Allows one object to notify multiple subscribers when its state changes (e.g., event listeners).
• Command – Encapsulates a request as an object, allowing undo/redo functionality (e.g., remote control buttons).
• Mediator – Defines an object that centralizes communication between components (e.g., chatroom mediator).
• State – Allows an object to change its behavior when its internal state changes (e.g., vending machine states).
• Chain of Responsibility – Passes requests along a chain of handlers until one processes it (e.g., logging system).
• Template Method – Defines a skeleton of an algorithm, allowing subclasses to implement specific steps.