Design Patterns Overview

Design patterns

Design Patterns: Elements of Reusable Object-Oriented Software as we know “the Gang Of Four” are the four authors of the book. They are:

described twenty three design pattern for object-oriented programming that categorized in this article. In this Design patterns series, we will provide

What are Design Patterns?

Design patterns provide solutions to common software design problems. In the case of object-oriented programming, design patterns are generally aimed at solving the problems of object generation and interaction, rather than the larger scale problems of overall software architecture. They give generalized solutions in the form of templates that may be applied to real-world problems.
The most important thing when we learn about design patterns is to understand the concepts that design patterns describe, rather than memorizing their exact class, methods and properties. Then we can apply patterns appropriately.

Gang of Four Design Patterns

We will list all twenty three design patterns described by the Gang of Four with the appropriate category.

Creational Patterns

The first type of design pattern is the creational pattern. Creational patterns provide ways to instantiate single objects or groups of related objects. There are five such patterns:

  • Factory: The Factory pattern is used to provide a client with a set of related or dependant objects. The “family” of objects created by the factory are determined at run-time. Go to Factory Design Pattern Example for more detail.
  • Builder: The builder pattern is used to create complex objects with constituent parts that must be created in the same order or using a specific algorithm. An external class controls the construction algorithm.
  • Factory Method: The factory pattern is used to replace class constructors, abstracting the process of object generation so that the type of the object instantiated can be determined at run-time.
  • Prototype: The prototype pattern is used to instantiate a new object by copying all of the properties of an existing object, creating an independent clone. This practise is particularly useful when the construction of a new object is inefficient.
  • Singleton: The singleton pattern ensures that only one object of a particular class is ever created. All further references to objects of the singleton class refer to the same underlying instance. Let’s check Post to Post Links II error: No post found with slug "singletons-pattern-overview" for more detail.

Structural Patterns

The second type of design pattern is the structural pattern. Structural patterns provide a manner to define relationships between classes or objects.

  • Adapter: The adapter pattern is used to provide a link between two otherwise incompatible types by wrapping the “adaptee” with a class that supports the interface required by the client. Let’s check Adapter Pattern: The right way for more detail.
  • Bridge: The bridge pattern is used to separate the abstract elements of a class from the implementation details, providing the means to replace the implementation details without modifying the abstraction.
  • Composite: The composite pattern is used to create hierarchical, recursive tree structures of related objects where any element of the structure may be accessed and utilised in a standard manner.
  • Decorator: The decorator pattern is used to extend or alter the functionality of objects at run-time by wrapping them in an object of a decorator class. This provides a flexible alternative to using inheritance to modify behaviour.
  • Facade: The facade pattern is used to define a simplified interface to a more complex subsystem. You can check Design Pattern: Facade Pattern in PHP for more detail.
  • Flyweight: The flyweight pattern is used to reduce the memory and resource usage for complex models containing many hundreds, thousands or hundreds of thousands of similar objects.
  • Proxy: The proxy pattern is used to provide a surrogate or placeholder object, which references an underlying object. The proxy provides the same public interface as the underlying subject class, adding a level of indirection by accepting requests from a client object and passing these to the real subject object as necessary.

Behavioural Patterns

The final type of design pattern is the behavioural pattern. Behavioural patterns define manners of communication between classes and objects.

  • Chain of Responsibility: The chain of responsibility pattern is used to process varied requests, each of which may be dealt with by a different handler parameters, in a command object. The command may then be executed immediately or held for later use.
  • Interpreter: The interpreter pattern is used to define the grammar for instructions that form part of a language or notation, whilst allowing the grammar to be easily extended.
  • Iterator: The iterator pattern is used to provide a standard interface for traversing a collection of items in an aggregate object without the need to understand its underlying structure.
  • Mediator: The mediator pattern is used to reduce coupling between classes that communicate with each other. Instead of classes communicating directly, and thus requiring knowledge of their implementation, the classes send messages via a mediator object.
  • Memento: The memento pattern is used to capture the current state of an object and store it in such a manner that it can be restored at a later time without breaking the rules of encapsulation.
  • Observer: The observer pattern is used to allow an object to publish changes to its state. Other objects subscribe to be immediately notified of any changes.
  • State: The state pattern is used to alter the behaviour of an object as its internal state changes. The pattern allows the class for an object to apparently change at run-time.
  • Strategy: The strategy pattern is used to create an interchangeable family of algorithms from which the required process is chosen at run-time.
  • Template Method: The template method pattern is used to define the basic steps of an algorithm and allow the implementation of the individual steps to be changed.
  • Visitor: The visitor pattern is used to separate a relatively complex set of structured data classes from the functionality that may be performed upon the data that they hold.

The details of all design patterns above will be described in other articles.

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