Gang of Four Design Patterns

GoF Design Patterns

Over 20 years ago the iconic computer science book “Design Patterns: Elements of Reusable Object-Oriented Software” was first published. The four authors of the book: Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, have since been dubbed “The Gang of Four”. In technology circles, you’ll often see this nicknamed shorted to GoF. Even though the GoF Design Patterns book was published over 20 years ago, it still continues to be an Amazon best seller.

The GoF wrote the book in a C++ context but it still remains very relevant to Java programming. C++ and Java are both object-oriented languages. The GoF authors, through their experience in coding large scale enterprise systems using C++, saw common patterns emerge. These design patterns are not unique to C++. The design patterns can be applied in any object oriented language.

As a Java developer using the Spring Framework to develop enterprise class applications, you will encounter the GoF Design Patterns on a daily basis.

The GoF Design Patterns are broken into three categories: Creational Patterns for the creation of objects; Structural Patterns to provide relationship between objects; and finally, Behavioral Patterns to help define how objects interact.

Gang of Four Design Patterns

Creational Design Patterns

  • Abstract Factory. Allows the creation of objects without specifying their concrete type.
  • Builder. Uses to create complex objects.
  • Factory Method. Creates objects without specifying the exact class to create.
  • Prototype. Creates a new object from an existing object.
  • Singleton. Ensures only one instance of an object is created.

Structural Design Patterns

  • Adapter. Allows for two incompatible classes to work together by wrapping an interface around one of the existing classes.
  • Bridge. Decouples an abstraction so two classes can vary independently.
  • Composite. Takes a group of objects into a single object.
  • Decorator. Allows for an object’s behavior to be extended dynamically at run time.
  • Facade. Provides a simple interface to a more complex underlying object.
  • Flyweight. Reduces the cost of complex object models.
  • Proxy. Provides a placeholder interface to an underlying object to control access, reduce cost, or reduce complexity.

Behavior Design Patterns

  • Chain of Responsibility. Delegates commands to a chain of processing objects.
  • Command. Creates objects which encapsulate actions and parameters.
  • Interpreter. Implements a specialized language.
  • Iterator. Accesses the elements of an object sequentially without exposing its underlying representation.
  • Mediator. Allows loose coupling between classes by being the only class that has detailed knowledge of their methods.
  • Memento. Provides the ability to restore an object to its previous state.
  • Observer. Is a publish/subscribe pattern which allows a number of observer objects to see an event.
  • State. Allows an object to alter its behavior when its internal state changes.
  • Strategy. Allows one of a family of algorithms to be selected on-the-fly at run-time.
  • Template Method. Defines the skeleton of an algorithm as an abstract class, allowing its sub-classes to provide concrete behavior.
  • Visitor. Separates an algorithm from an object structure by moving the hierarchy of methods into one object.

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16 comments on “Gang of Four Design Patterns

  1. April 28, 2015 at 1:00 am

    When there are only 3 categories why call it GANG OF FOUR?

    Reply
    • April 28, 2015 at 5:14 am

      “Gang of Four” refers to the four authors of the book – Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides.

      Reply
  2. March 5, 2018 at 2:15 am

    John, appreciate your efforts in explaining GoF patterns in detail and also with great quality covering OO Design principles, etc.
    Your blog is one of the top best which covers these patterns.

    Thanks for sharing the knowledge.

    Reply
    • March 7, 2018 at 4:36 pm

      Thanks!

      Reply
  3. March 16, 2018 at 5:19 pm

    Thanks John, For explaining Design patterns with excellent examples.

    Reply
  4. March 27, 2018 at 7:54 am

    Give one more i to the visitor in your last line 😉

    Reply
  5. April 12, 2018 at 9:23 am

    Hi John,

    Could you please tell me exactly which patterns are being used in a simple spring application. (Basic CRUD functionality)

    Regards,

    Gavin

    Reply
  6. November 27, 2018 at 10:09 am

    This post keeps me coming back to refresh my knowledge. Thanks so much!

    Reply
  7. December 4, 2018 at 3:14 am

    It’s a great place to learn design patterns for people who want to start implementing scalable applications!!
    Thanks John, really appreciate your effort a lot!

    Reply
  8. December 21, 2018 at 11:41 am

    Finding a design pattern blog post that stitches together ideas has been challenging. This blog has become my go-to since I stumbled upon it. Really love your style of writing. If I’d to add one thing that could be improved, it would be adding pros/cons about the pattern.

    Reply
  9. January 15, 2019 at 5:53 pm

    I have an idea for a GoF Design Patterns spin-off. A good suggested name might be:

    Design Patterns II

    Elements of Reusable Object-Oriented and Functional Javascript
    (Spinoff greatly inspired by Gang-of-Four Design Patterns)

    Inspired by original GoF Design Patterns a 2nd edition would be published citing all 23 or so commonly used or most important design patterns employing only JavaScript or related web development languages where Javascript examples are not appropriate for example CSS variables or serverless databases. A pro edition would also be available for other patterns (perhaps 32 in all) not in the original Design Patterns by GoF. Abstract to concrete real world examples would all be written from Vanilla to Neapolitan flavored Javascript. New edition would make very limited use of jQuery. Examples of in-the-wild popular libraries/frameworks would cite instances where they did it right and where they went wrong. Not a single use of the non-words “foo” and “bar” are printed anywhere in the book as such abstractions are so bland and meaningless that novice programmers often have difficulty grasping the core lessons behind them — novice programmers like me.

    Several outstanding books have already been written for example Learning JavaScript Design Patterns (Volume 1.7.0 is completely free online) by Addy Osmani. But the examples are too bland for me. He should have kade use of more real-world examples especially from frameworks. There is also a great website called refactoring.guru giving one a taste of design patterns (also inspired by GoF) or the full book for a small price but he uses fucking cats and other dumb real-world objects to demonstrate use-cases in UML. UML is too much of an abstraction. Beginners to intermediate programmers need real-world example to really grasp the core ideas.

    My programming skills are far too low to write/co-write or technically review such a book. But if said book were to be published l would be near the top of a very long list to acquire an initial beta release. I just wanted to throw that out there to get your thoughts.

    What do you all think of this idea?

    Reply
  10. May 22, 2019 at 3:36 am

    Is there any architectural design pattern??

    Reply

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