Design patterns

Design patterns

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 patterns

Patterns are a toolkit of solutions to common problems in software design. They define a common language that helps your team communicate more efficiently.

Classification of patterns

In addition, all patterns can be categorized by their intent, or purpose. This book covers three main groups of patterns:

• Creational patterns provide object creation mechanisms that increase flexibility and reuse of existing code.

• Structural patterns explain how to assemble objects and classes into larger structures, while keeping these structures flexible and efficient.

• Behavioral patterns take care of effective communication and the assignment of responsibilities between objects.

Creational patterns

These patterns provide various object creation mechanisms, which increase flexibility and reuse of existing code.

Structural patterns

These patterns explain how to assemble objects and classes into larger structures while keeping these structures flexible and efficient.

Behavioral patterns

These patterns are concerned with algorithms and the assignment of responsibilities between objects.

Factory Method

is a creational design pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

Factory Method

Abstract Factory

is a creational design pattern that lets you produce families of related objects without specifying their concrete classes.

Abstract Factory

Builder

is a creational design pattern that lets you construct complex objects step by step. The pattern allows you to produce different types and representations of an object using the same construction code.

Builder

Prototype

is a creational design pattern that lets you copy existing objects without making your code dependent on their classes.

Prototype

Singleton

is a creational design pattern that lets you ensure that a class has only one instance, while providing a global access point to this instance.

Singleton

Adapter

is a structural design pattern that allows objects with incompatible interfaces to collaborate.

Adapter

Bridge

is a structural design pattern that 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.

Bridge

Composite

is a structural design pattern that lets you compose objects into tree structures and then work with these structures as if they were individual objects.

Composite

Decorator

is a structural design pattern that lets you attach new behaviors to objects by placing these objects inside special wrapper objects that contain the behaviors.

Decorator

Facade

is a structural design pattern that provides a simplified interface to a library, a framework, or any other complex set of classes.

Facade

Flyweight

is a structural design pattern that 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.

Flyweight

Proxy

is a structural design pattern that 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.

Proxy

Chain of Responsibility

is a behavioral design pattern that 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.

Chain of Responsibility

Command

is a behavioral design pattern that turns a request into a stand-alone object that contains all information about the request. This transformation lets you pass requests as a method arguments, delay or queue a request’s execution, and support undoable operations.

Command

Iterator

is a behavioral design pattern that lets you traverse elements of a collection without exposing its underlying representation (list, stack, tree, etc.).

Iterator

Mediator

is a behavioral design pattern that 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.

Mediator

Memento

is a behavioral design pattern that lets you save and restore the previous state of an object without revealing the details of its implementation.

Memento

Memento Interface

Observer

is a behavioral design pattern that lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.

Observer

State

is a behavioral design pattern that lets an object alter its behavior when its internal state changes. It appears as if the object changed its class.

State

Strategy

is a behavioral design pattern that lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.

Strategy

Template Method

is a behavioral design pattern that defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.

Template Method

Visitor

is a behavioral design pattern that lets you separate algorithms from the objects on which they operate.

Visitor