Design patterns in software development

Design patterns in software development

Published on Dec 31, 2019

Reading time: 6 minutes.


Design patterns are reusable solutions to commonly occurring software design problems. They provide a common vocabulary for developers to use when discussing design concepts and can help simplify complex design decisions.

There are many different design patterns, but here are some of the most commonly used:

Creational Patterns: These patterns provide a way to create objects while hiding the creation logic from the client. Some examples include the Singleton, Factory, and Abstract Factory patterns.

Structural Patterns: These patterns help organize classes and objects into larger structures. Some examples include the Adapter, Bridge, and Decorator patterns.

Behavioral Patterns: These patterns define how objects interact with one another. Some examples include the Observer, Command, and Strategy patterns.

Architectural Patterns: These patterns are larger scale patterns that define the overall structure of a system. Some examples include the Model-View-Controller (MVC), Layered Architecture, and Microservices patterns.

When applying design patterns, it’s important to keep in mind that they are not a one-size-fits-all solution. You should always consider the specific needs of your project and choose the patterns that will best solve your particular problems.

Also, design patterns should not be seen as a rigid set of rules that must be followed at all times. They are merely guidelines that can be adapted and modified as needed to fit the requirements of your project.

Here are some more details about each type of design pattern and some examples of patterns within each type:

Creational Patterns: These patterns are used to create objects in a way that is flexible and decoupled from the code that uses them. Examples include:

Singleton Pattern: This pattern ensures that only one instance of a class is created, and provides a global point of access to that instance.
Factory Pattern: This pattern provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.
Abstract Factory Pattern: This pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes.

Structural Patterns: These patterns are used to organize classes and objects in a way that makes them easier to understand and work with. Examples include:

Adapter Pattern: This pattern allows two incompatible interfaces to work together by wrapping one interface in a compatible adapter.
Bridge Pattern: This pattern separates an abstraction from its implementation, allowing them to vary independently of each other.
Decorator Pattern: This pattern allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class.

Behavioral Patterns: These patterns are used to manage interactions between objects and the control flow of a program. Examples include:

Observer Pattern: This pattern defines a one-to-many relationship between objects so that when one object changes state, all of its dependents are notified and updated automatically.
Command Pattern: This pattern encapsulates a request as an object, allowing it to be treated as a first-class citizen and giving clients the ability to parameterize and queue requests.
Strategy Pattern: This pattern allows interchangeable algorithms to be selected at runtime, without affecting the client that uses them.

Architectural Patterns: These patterns are used to define the overall structure of a software system. Examples include:

Model-View-Controller (MVC) Pattern: This pattern separates an application into three interconnected components: the model (data), the view (user interface), and the controller (logic).
Layered Architecture Pattern: This pattern divides an application into layers, with each layer responsible for a specific set of tasks, such as data storage or user interface.
Microservices Pattern: This pattern structures an application as a set of small, independently deployable services that communicate with each other through APIs.

Here’s a deeper explanation of each of the design patterns mentioned before, along with some examples:

Creational Patterns:

Singleton Pattern: This pattern ensures that only one instance of a class is created, and provides a global point of access to that instance. This can be useful for situations where you only want one instance of an object to exist throughout the lifetime of an application, such as a logger or a database connection.

Example: A logging class that writes messages to a file could be implemented as a singleton, so that all parts of the application share the same logging instance and write to the same log file.

Factory Pattern: This pattern provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created. This can be useful for situations where you want to delegate object creation to subclasses, or when you need to create objects dynamically based on some input or condition.

Example: A GUI framework might use a factory pattern to create different types of UI elements (such as buttons or text boxes) depending on the user’s platform or preferences.

Abstract Factory Pattern: This pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes. This can be useful for situations where you need to create objects that are part of a larger system or subsystem, and where the details of object creation need to be abstracted away.

Example: A car manufacturing system might use an abstract factory pattern to create different types of components (such as engines or wheels) depending on the type of car being produced.

Structural Patterns:

Adapter Pattern: This pattern allows two incompatible interfaces to work together by wrapping one interface in a compatible adapter. This can be useful for situations where you need to integrate existing code or systems that use different interfaces or data formats.

Example: A legacy system might use a proprietary data format that is incompatible with newer systems. An adapter could be used to translate between the two formats, allowing the systems to communicate with each other.

Bridge Pattern: This pattern separates an abstraction from its implementation, allowing them to vary independently of each other. This can be useful for situations where you need to decouple different parts of a system that might change independently of each other.

Example: A drawing application might use a bridge pattern to separate the high-level abstraction of a shape (such as a circle or square) from its low-level implementation (such as its drawing method or color).

Decorator Pattern: This pattern allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class. This can be useful for situations where you need to add functionality to an object in a flexible or modular way.

Example: A text editor might use a decorator pattern to add formatting or other special features to individual words or phrases within a document.

Behavioral Patterns:

Observer Pattern: This pattern defines a one-to-many relationship between objects so that when one object changes state, all of its dependents are notified and updated automatically. This can be useful for situations where you need to keep different parts of a system synchronized with each other.

Example: A stock market application might use an observer pattern to notify different users or systems when a stock’s price changes.

Command Pattern: This pattern encapsulates a request as an object, allowing it to be treated as a first-class citizen and giving clients the ability to parameterize and queue requests. This can be useful for situations where you need to decouple the requester of an action from the object that performs the action.

Example: A text editor might use a command pattern to allow users to undo or redo a series of changes made to a document.

Strategy Pattern: This pattern allows interchangeable algorithms to be selected at runtime, without affecting the client that uses them.