iluwatar / java-design-patterns

Design patterns implemented in Java

Design patterns implemented in Java

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Introduction

Design patterns are the best, formalized practices a programmer can use to solve common problems when designing an application or system.

Design patterns can speed up the development process by providing tested, proven development paradigms.

Reusing design patterns helps prevent subtle issues that cause major problems, and it also improves code readability for coders and architects who are familiar with the patterns.

Getting started

This site showcases Java Design Patterns. The solutions have been developed by experienced programmers and architects from the open-source community. The patterns can be browsed by their high-level descriptions or by looking at their source code. The source code examples are well commented and can be thought of as programming tutorials on how to implement a specific pattern. We use the most popular battle-proven open-source Java technologies.

Before you dive into the material, you should be familiar with various Software Design Principles.

All designs should be as simple as possible. You should start with KISS, YAGNI, and Do The Simplest Thing That Could Possibly Work principles. Complexity and patterns should only be introduced when they are needed for practical extensibility.

Once you are familiar with these concepts you can start drilling down into the available design patterns by any of the following approaches

• Search for a specific pattern by name. Can't find one? Please report a new pattern here.
• Using tags such as Performance, Gang of Four or Data access.
• Using pattern categories, Creational, Behavioral, and others.

Hopefully, you find the object-oriented solutions presented on this site useful in your architectures and have as much fun learning them as we had while developing them.

How to contribute

If you are willing to contribute to the project you will find the relevant information in our developer wiki. We will help you and answer your questions in the Gitter chatroom.

License

This project is licensed under the terms of the MIT license.

Contributors

Ilkka Seppälä 📆 🚧 🖋	Subhrodip Mohanta 💻 👀 🚧	amit1307 💻	Narendra Pathai 💻 🤔 👀	Jeroen Meulemeester 💻	Joseph McCarthy 💻	Thomas 💻
Anurag Agarwal 💻	Markus Moser 🎨 💻 🤔	Sabiq Ihab 💻	Amit Dixit 💻	Piyush Kailash Chaudhari 💻	joshzambales 💻	Kamil Pietruszka 💻
Zafar Khaydarov 💻 📖	Paul Campbell 💻	Argyro Sioziou 💻	TylerMcConville 💻	saksham93 💻	nikhilbarar 💻	Colin But 💻
Ruslan 💻	Juho Kang 💻	Dheeraj Mummareddy 💻	Bernardo Sulzbach 💻	Aleksandar Dudukovic 💻	Yusuf Aytaş 💻	Mihály Kuprivecz 💻
Stanislav Kapinus 💻	GVSharma 💻	Srđan Paunović 💻	Petros G. Sideris 💻	Pramod Gupta 👀	Amarnath Chandana 💻	Anurag870 💻 📖
Wes Gilleland 💻	Harshraj Thakor 💻	Martin Vandenbussche 💻	Alexandru Somai 💻	Artur Mogozov 💻	anthony 💻	Christian Cygnus 💻
Dima Gubin 💻	Joshua Jimenez 💻	Kai Winter 💻	lbroman 💻	Przemek 💻	Prafful Agarwal 🖋	Sanket Panhale 🖋
staillebois 💻	Krisztián Nagy 💻	Alexander Ivanov 💻	Yosfik Alqadri 💻	Agustí Becerra Milà 💻	Juan Manuel Suárez 💻	Luigi Cortese 💻
Katarzyna Rzepecka 💻	adamski.pro 💻	Shengli Bai 💻	Boris 💻	Dmitry Avershin 💻	靳阳 💻	hoangnam2261 💻
Arpit Jain 💻	Jón Ingi Sveinbjörnsson 💻	Kirill Vlasov 💻	Mitchell Irvin 💻	Ranjeet 💻	PhoenixYip 💻	M Saif Asif 💻
kanwarpreet25 💻	Leon Mak 💻	Per Wramdemark 💻	Evan Sia Wai Suan 💻	AnaghaSasikumar 💻	Christoffer Hamberg 💻	Dominik Gruntz 💻
Hannes 💻	Leo Gutiérrez Ramírez 💻	Zhang WH 💻	Christopher O'Connell 💻	George Mavroeidis 💻	Hemant Bothra 💻 🎨	Kevin Peters 💻
George Aristy 💻	Mahendran Mookkiah 💻	Azureyjt 💻	gans 💻	Matt 🖋	Gopinath Langote 💻	Hoswey 💻
Amit Pandey 💻	gwildor28 🖋	田浩 🖋	Stamatis Pitsios 💻	qza 💻	Rodolfo Forte 🖋	Ankur Kaushal 💻
Ovidijus Okinskas 💻	Robert Kasperczyk 💻	Tapio Rautonen 💻	Yuri Orlov 💻	Varun Upadhyay 💻	Aditya Pal 💻	grzesiekkedzior 💻 👀
Sivasubramani M 💻	Sami Airaksinen 💻	Janne Sinivirta 💻	Boris-Chengbiao Zhou 🖋	Jacob Hein 🖋	Richard Jones 🖋	Rachel M. Carmena 🖋
Zaerald Denze Lungos 🖋	Lars Kappert 🖋	Mike Liu 🌍	Matt Dolan 💻 👀	Manan 👀	Nishant Arora 💻	Peeyush 💻
Rakesh 💻 👀	Wei Seng 💻	Ashish Trivedi 💻	洪月阳 💻	xdvrx1 👀 🤔	Bethan Palmer 💻	Toxic Dreamz 💻
Edy Cu Tjong 📖	Michał Krzywański 💻	Stefan Birkner 💻	Fedor Skvorcov 💻	samilAyoub 💻	Vladislav Golubinov 💻	Swaraj 💻
Christoph Flick 📖	Ascênio 👀	Domenico Sibilio 📖	Akash Chandwani 👀	Pavlo Manannikov 💻	Eiman 💻	Rocky 📖
Ibrahim ali abdelghany 👀	Girish Kulkarni 📖	Omar Karazoun 💻	Jeff Evans 💻	Vivek Singh 💻	siavash 💻	ruchpeanuts 📖
warp125 🌍	KHADIR Tayeb 🌍	ignite1771 💻	Halil Demir 🌍	Rohit Singh 💻	byoungju94 💻	Moustafa Farhat 🌍
Martel Richard 💻	va1m 💻	Noam Greenshtain 💻	yonghong Xu 📖	jinishavora 👀 💻	Elvys Soares 💻	zWeBrain 💻
余林颖 🌍	Alain 🌍	VR 📖	JackieNim 💻	EdisonE3 💻	Tao 💻	Juan Manuel Abate 🌍
Xenilo137 💻	Samuel Souza 💻	Marlo Henrique 🌍	AndriyPyzh 💻	karthikbhat13 💻	Morteza Adigozalpour 💻	Nagaraj Tantri 💻
Francesco Scuccimarri 💻	Conny Hansson 📖	Muklas Rahmanto 🌍	Vadim 🌍	Simran Keshri 💻	JCarlos 🌍	Ali Ghasemi 💻
Carl Dea 💻	Mozartus 🌍	Manvi Goel 📖	Anum Amin 📖	Reo Uehara 🌍	Fiordy 📖	Harshal 💻
Abhinav Vashisth 📖	Kevin 👀 💻	Shrirang 👀 💻	interactwithankush 💻	CharlieYu 💻	Leisterbecker 💻	DragonDreamer 💻
ShivanshCharak 💻	HattoriHenzo 💻	Arnab Sen 💻	MohanaRao SV 💻	Yonatan Karp-Rudin 💻 👀	Oliani 💻	Renjie LIU 💻
perfect guy 📖	xyllq999 💻	Mohamed Bilal 📖	Karshil sheth 💻	kongleong86 💻	Aitor Fidalgo Sánchez 🌍 📖 👀	Victor He 💻
Minh Nguyen 🌍 📖	Victor He 📖	yiichan 📖	Pan Sem 📖	zhoumengyks 💻	you 🌍	Thanks 🌍
LazyProgrammer 📖	Mohammed Faizan Ahmed 📖	Bruno Fernandes 💻	SammanPali 📖	Qixiang Chen 📖	Shourya Manekar 🌍	Alan 🌍
JanFidor 💻 📖	Anton Yakutovich 💻	steph88ss 📖	Yujan Ranjitkar 🌍	yusha-g 🌍	Robert Volkmann 💻 👀	Bipin Kumar Chaurasia 📖
KyleSong30 📖	u7281975 📖	harshalkhachane 💻	Tejas Singh 📖 🌍	Sudarsan Balaji 💻	Vaibhav Agrawal 📖	u7275858 💻
prasad-333 📖	JurenXu 💻	murphShaw 📖	XianWu99 📖	JoshuaSinglaANU 💻	Ricardo Ramos 🌍	Farid Zouheir 🌍
Vinícius A. B. 🌍	Stefanel Stan 💻	Prince bhati 🌍	WuLang 📖	Hugo Kat 💻	Shivanagouda Agasimani 💻	Aparna 💻
Girolamo Giordano 🌍	Chak-C 💻	Nakul Nambiar 💻	KarmaTashiCat 🌍	marikattt 💻	Hashvardhan Parmar 🌍	YongHwan 📖 🌍
Shogo Hida 🌍	Eugene 💻	Piyush 📖	Rahul Raj 💻	Bharath Kalyan S 💻	Saiteja Reddy 🌍	Enrique Clerici 🌍
Ramil Sayetov 🌍	东方未白 💻	Fredrik Sejr 🌍	akshatarora0013 💻	Mughees Qasim 💻	behappyleee 🌍	Ayush Thakur 🌍
Anthony Bosch 💻	trananso 📖	Giammaria Biffi 🌍	Saiful Haque 💻	JabezBrew 💻	konstantin-goldman 📖	Tien Nguyen Minh 💻 🌍
Vladimir 🌍	Surjendu 🌍 💻	bakazhou 💻	Owen Leung 💻	Stavros Barousis 📖	Syyed Ibrahim Abdullah 🌍	JiaDi Zhang 🌍
Sanchit Bansal 📖	Md Saiful Islam 📖	Antonio Addeo 📖 💻	Allagadda Sai Upendranath 📖	Matheus Braga 🌍 📖	Appari Satya Barghav 📖	Marcel Ribeiro-Dantas 📖
Muhammad Hanif Amrullah 🌍	JackH408 📖	Shubham 🌍	Nishant Jain 📖	Rhitam Chaudhury 📖	JerryZhao275 📖	Leonardo Lisanti 🌍
Yennifer Herrera 🌍 👀	jnniu-n 🌍 📖	Miguel Angel Perez Garcia 👀 🌍	Suwan Sankaja 🌍	alok 📖	Daniel Lisboa 🌍	Sam Powell 📖
João Fernandes 🌍	Hong Geon-ui 🌍	Doksanbir 💻 📖 👀	Chant3ll3 📖 🌍	YongHwan Kwon 💻	Jakub Klimek 💻	believe 🌍
egg0102030405 🌍 📖	Ved Asole 💻	NewMorning 🌍	资深老萌新 🌍	Seunghwan Jeon 🌍	sugavanesh 💻	FinnS-F 💻
jerryyummy 🌍	Manoj Chowdary 💻	Aditya 📖 💻	nooynayr 📖	CYBERCRUX2 📖	Luis Mateo Hincapié Martinez 🌍 👀	guqing 💻
Sashir Estela 💻	omahs 📖	leif e. 💻	Jun Kang 💻	Kishalay Pandey 💻	drishtii7 💻	David Medina Orozco 🌍 👀
Roman Leontev 💻	Riley 💻

java-design-patterns's Issues

Async Method Invocation pattern

https://en.wikipedia.org/wiki/Asynchronous_method_invocation

Practical explanations

First, I'd like to thank you for providing the examples, really great job! However, I'd like more practical explanations since currently they are rather theoretical and hard to understand, don't you think?

For example the Builder pattern, I've read the explanation and honestly do not know when to use in my daily work. Wouldn't it be better just to write that you use it if you have few required and many optional construction parameters?

DAO Design Pattern

Hi @iluwatar ,

First of all, thank you for this comprehensive repo! I haven't seen the dao design pattern among the rest. So, I am just wondering whether it is actually part of the design solutions or not.

Readers-writer lock

https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock

Bug introduced by #11

@llitfkitfk You made ALL the diagrams link to files from your FORK. The BASE readme is pointing to files from a FORK.

commit hash is 97431a62af9881fa046b69b690e72d4fb4777209

StarMemento would expose the internal state of Star object in memento patterns

How about making startMemento an inner class of Start class?

Parallel Change pattern

http://martinfowler.com/bliki/ParallelChange.html

Messaging (EIP)

https://en.wikipedia.org/wiki/Messaging_pattern

Balking pattern

https://en.wikipedia.org/wiki/Balking_pattern

Monostate pattern

http://www.objectmentor.com/resources/articles/SingletonAndMonostate.pdf
http://c2.com/cgi/wiki?MonostatePattern

Data Mapper Pattern

Hi, I'm a new user to github and I would like to help to this project. I've been researching about a few patterns and the work you've done and I think it's so cool.

In my college I've developed an application which comunicates with a MySQL Database and I had to build a pattern to make that communication work. I'm talking about the Abstract Mapper.

I have an example here: https://github.com/jesusvazquez/java_examples/tree/master/AdvancedDatabaseSystems/src/modelo/DBMapper

I'm wondering if it would be a good idea to add this pattern to your project.

Best Regards.

Model View ViewModel (MVVM) pattern

https://en.wikipedia.org/wiki/Model_View_ViewModel

Guarded suspension pattern

https://en.wikipedia.org/wiki/Guarded_suspension

Layers architectural pattern

https://en.wikipedia.org/wiki/Multilayered_architecture

Not have private constructor in the thread-safe Singleton class ?

hello iluwatar

when I read the Singleton pattern ,the ThreadSafeLazyLoadedIvoryTower class use the default constructor method ,you don't specify it ，should it right ?
I think must add a private constructor as the IvoryTower class.
is it right?

Intercepting Filter example needs some improvement

• FilterChain executes the filters sequentially using an array. This should be changed so that the filters form a chain and call each other instead. Like in Chain of Responsibility.
• At the same time the feedback mechanism from the filters should be improved. This should be implemented with Collecting Parameter idiom. It should be possible to return multiple errors from the filter chain. The current implementation can handle only one.
• The data passed to the filters should be transformed into value object from string array. This way we can get rid of magic numbers (array index) in filters.

Hexagonal architecture

http://www.dossier-andreas.net/software_architecture/ports_and_adapters.html

Idea.

Add the "real" project(or link to good project) where the most of patterns will be represented.And fully documented.To see how they used in real life.For example text editor.Or something else.

Add virtual field pattern

There's a new (I think) pattern called the Virtual field pattern, introduced in Java 8. https://kerflyn.wordpress.com/2012/07/09/java-8-now-you-have-mixins/ Scroll half way through till you find "Another Approach".

Microservices patterns

http://microservices.io/patterns/index.html

Active Object concurrency pattern

https://en.wikipedia.org/wiki/Active_object

Front Controller pattern

https://en.wikipedia.org/wiki/Front_Controller_pattern

Twin design pattern

http://www.ssw.uni-linz.ac.at/Research/Papers/Moe99/Paper.pdf

Scheduler pattern

https://en.wikipedia.org/wiki/Scheduler_pattern

not a issue,just want to know

hey,I see a file ends with ucls in some package,I open it and find it is an xml format file
and my question is what kind of soft you draw it
Thanks!

Blackboard architectural pattern

Better View/Navigation ?

Heya there,
first of all, i love this resource and use it quite often. the only thing slightly annoying is the layout. Would be really awesome to view this resource in bootstrap with categories or something like that.

If something like that is done "hardcoded" the project will probably loose on contributions, so a converter of sorts should be used.

One last point, i found this Site that looks pretty good, but i dont know if it would be suitable. I also have no idea if it even works, because here everything is one single markdown document, while those at the site are multiple.
http://phpmyadmin.readthedocs.org/en/QA_4_4/
(topic is not important)

Just an idea C:

~Markus

Pipes And Filters (EIP)

https://code.google.com/p/pipelinepattern/

Module pattern

https://en.wikipedia.org/wiki/Module_pattern

Proactor pattern

https://en.wikipedia.org/wiki/Proactor_pattern

Monitor pattern

https://en.wikipedia.org/wiki/Monitor_(synchronization)

What is the use of UML drawing software

Can you tell me the UML diagram is used what software to draw?

Facet pattern

http://www.hillside.net/plop/plop2002/final/plop2002_ecrahen0_0.pdf

Lock pattern

https://en.wikipedia.org/wiki/Lock_(computer_science)

HeroBuilder NullPointerException

I was reading the code and then I wondered why was used the NullPointerException in that case, won't be more readable throw a custom exception? I mean create something like BuilderException and then this can be treated in the caller method ...
*Line 97,98 from HeroBuilder.java for reference

Binding Properties pattern

http://c2.com/cgi/wiki?BindingProperties

Active Record pattern

https://en.wikipedia.org/wiki/Active_record_pattern

Repository

Great job.
How about repository?
Reference: http://martinfowler.com/eaaCatalog/repository.html

Join pattern

https://en.wikipedia.org/wiki/Join-pattern

Null object as a singleton

It is recommended to implement null object as a singleton.

In the example, NullNode (https://github.com/iluwatar/java-design-patterns/blob/master/null-object/src/main/java/com/iluwatar/NullNode.java) is not a singleton.

Thread local storage pattern

https://en.wikipedia.org/wiki/Thread-local_storage

Cloud design patterns

http://download.microsoft.com/download/B/B/6/BB69622C-AB5D-4D5F-9A12-B81B952C1169/CloudDesignPatternsBook-PDF.pdf

Documentation change in DAO pattern

Removed a redundant word and added an Acronym.

Add code coverage analysis

We could use this: https://github.com/trautonen/coveralls-maven-plugin

Business Delegate pattern

http://www.oracle.com/technetwork/java/businessdelegate-137562.html

please help me , thanks !

Hello, may I ask you what software tool to draw a class diagram?

I want to get it.

Can you send it to my email ? Or tell me what its name . Thank you very much!

My email : [email protected]

New patterns

Is it possible that we add web application and database patterns here as well? By web application patterns, I mean

1. Single Thread pattern
2. Synchronization pattern in MVC
3. Double checked locking
4. Service locator
5. Facade
   ..... (any more that we can think of)

and the database patterns I had the data access (DAO) pattern in mind.

Clean architecture

http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html

Add static code analysis

Reactor pattern

https://en.wikipedia.org/wiki/Reactor_pattern