What are the main categories of Design Patterns?

Design patterns are typically categorized into three main categories:

  1. Creational Patterns: Creational patterns focus on object creation mechanisms, providing ways to create objects in a manner that is flexible, decoupled, and reusable. Some common creational patterns include:
    • Singleton: Ensures that only one instance of a class is created and provides a global point of access to it.
    • Factory Method: Defines an interface for creating objects, 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 complex objects from their representation, allowing the same construction process to create different representations.
    • Prototype: Creates new objects by cloning existing ones, thus avoiding the need for explicit class instantiation.
  2. Structural Patterns: Structural patterns deal with the composition of classes and objects, focusing on how they are organized to form larger structures while keeping them flexible and efficient. Some common structural patterns include:
    • Adapter: Converts the interface of a class into another interface that clients expect, allowing classes with incompatible interfaces to work together.
    • Composite: Represents objects in a tree-like structure, allowing clients to treat individual objects and compositions uniformly.
    • Decorator: Dynamically adds behavior to objects by wrapping them in an object of a decorator class, providing a flexible alternative to subclassing.
    • Facade: Provides a simplified interface to a complex system, acting as a high-level interface that makes the system easier to use.
    • Proxy: Provides a surrogate or placeholder for another object to control its access, add additional functionality, or defer expensive operations.
  3. Behavioral Patterns: Behavioral patterns focus on the interaction and communication between objects, defining patterns for the effective communication and coordination among classes and objects. Some common behavioral patterns include:
    • Observer: Defines a one-to-many dependency between objects, so that when one object changes its state, all its dependents are notified and updated automatically.
    • Strategy: Defines a family of interchangeable algorithms and encapsulates each one, allowing them to be used interchangeably based on specific requirements.
    • Command: Encapsulates a request as an object, allowing clients to parameterize clients with different requests, queue or log requests, and support undoable operations.
    • Iterator: Provides a way to access the elements of an aggregate object sequentially, without exposing its underlying representation.
    • State: Allows an object to alter its behavior when its internal state changes, effectively changing its class dynamically.

These categories provide a high-level classification of design patterns based on their primary focus. However, some patterns may not fit neatly into a single category, and there are other pattern classification schemes as well. It’s important to understand the characteristics and intent of each pattern to effectively apply them in software design.

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