Design pattern are typical solutions to common problems in software design.
Each pattern is like a blueprint that you can customize to solve a particular design problem in your code.
Benefits of Using Design Patterns
It's solution to common problems that software design.
They also define common language for developers, making it easier to communicate ideas and solutions.
Classification of Design Patterns
All patterns can be categorized by their purpose. The three main categories are:
Creational Patterns: provide object creation mechanisms that increase flexibility and reuse of existing code. Examples include Singleton, Factory Method, and Abstract Factory.
Structural Patterns: explain how to assemble objects and classes into larger structures. While keeping these structure flexible and efficient. Examples include Adapter, Composite, and Decorator.
Behavioral Patterns: takes care of effective communication and the assignment of responsibilities between objects. Examples include Observer, Strategy, and Command.
Creational Patterns
Factory Method : Provide an interface for creating objects in a superclass, but allow subclasses to alter the type of objects that will be created.
Abstract Factory : Lets you produce families of related objects without specifying their concrete classes.
Builder : Lets you construct complex objects step by step. The construction process can create different representations and provides a high level of control over the construction process.
Prototype : Lets you copy existing objects without making your code dependent on their classes.
Singleton : Lets you ensure that a class has only one instance, while providing a global access point to this instance.
Structural Patterns
Adapter : Provide a unified interface that allows objects with incompatible interfaces to work together.
Bridge : Lets you split a large class or a set of closely related classes into two separate hierarchies—abstraction and implementation—which can be developed independently of each other.
Composite : Lets you compose objects into tree structures and then work with these structures as if they were individual objects.
Decorator : Lets you attach new behaviors to objects by placing them inside special wrapper objects that contain the behaviors.
Facade : Provides a simplified interface to a larger body of code, such as a class library.
Flyweight : Lets you fit more objects into the available amount of RAM by sharing common parts of state between multiple objects instead of keeping all of the data in each object.
Proxy : Lets you provide a substitute or placeholder for another object. A proxy controls access to the original object, allowing you to perform something either before or after the request gets through to the original object.
Behavioral Patterns
Chain of Responsibility : Lets you pass requests along a chain of handlers. Upon receiving a request, each handler decides either to process the request or to pass it to the next handler in the chain.
Command : Turns a request into a stand-alone object that contains all information about the request. This transformation lets you parameterize methods with different requests, delay or queue a request’s execution, and support undoable operations.
Iterator : Let you transverse elements of a collection without exposing its underlying representation (list, stack, tree, etc.).
Mediator : Lets you reduce chaotic dependencies between objects. The pattern restricts direct communications between the objects and forces them to collaborate only via a mediator object.
Memento : Lets you save and restore the previous state of an object without revealing the details of its implementation.
Observer : Lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.
State : Lets an object alter its behavior when its internal state changes. It appears as if the object changed its class.
Strategy : Lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
Template Method : Defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.
Visitor : Lets you separate algorithms from the objects on which they operate.