Dear Dan, besides listing the patterns, could you in these years try to define them? I would really like to see whatever you or other did. Thank you in advance for any hint, riccardo. Your email address will not be published. The OpenScience Project. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently. Click to zoom News Publisher Example. Observer - Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
Click to zoom Robot Example. Strategy - Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it. Click to zoom Travel Example. Click to zoom Customers Example. Null Object - Provide an object as a surrogate for the lack of an object of a given type.
Adapter - Convert the interface of a class into another interface clients expect. Click to zoom Click to zoom. Bridge - Compose objects into tree structures to represent part-whole hierarchies. Click to zoom Shapes Example. Composite - Compose objects into tree structures to represent part-whole hierarchies. Click to zoom GUI Example. Decorator - add additional responsibilities dynamically to an object.
Click to zoom Wargame Example. Flyweight - use sharing to support a large number of objects that have part of their internal state in common where the other part of state can vary. Click to zoom Calculator Example. Memento - capture the internal state of an object without violating encapsulation and thus providing a mean for restoring the object into initial state when needed. Click to zoom Image Viewer.
Design Pattern Books. What Design Pattern To Choose? Design Principles and Patterns. Home Home. Arrows in the above read as "dependent-on" show high-level code directly dependent on details of low-level code it needs their names to create them via new This picture shows how the depenencies get inverted whan a factory method is used, meaning PizzaStore only deals with Pizza abstraction, not all the low-level details.
The dependencies were inverted - D-I-P! Abstract Factory Refactoring. It probably doesn't deserve to be a design pattern, its just one of many variations possible on factories. Proxy Refactoring. Proxy is a special case of delegation where nearly all methods of one object delegate to the same method in another object.
Virtual Proxy : maybe actual object hasn't been created or loaded yet -- for example when browsing thumbnails you don't need the full Picture object, a PictureProxy in the middle may only have the thumbnail loaded and can itself load the Picture into memory if needed Proxies can be used for access control: e.
ReadOnlyGoober could be a proxy class for a Goober which does not forward setter messages to Goober , but forwards all others.
Java RMI uses remote proxies for remote objects, and Hibernate uses proxies for database-stored objects.
Template Method Refactoring. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure. Generic diagram Template method is needed if subclasses have methods that are similar violating DRY but also have different bits so it cannot be directly lifted to superclass.
The template is an algorithm with code in the superclass but which has "holes" steps not yet known at the superclass level in it. The subclasses implement the "holes" The steps in the algorithm common to all implementations can be in the superclass notice how this avoids code duplication the subclasses provide the missing bits by instantiating some methods that were abstract in the superclass. Example code for coffee or tea brewing; diagram of this example See also the Form Template Method refactoring Design principle: the hollywood principle Don't call us, we'll call you Translation: Context: a high-level component is talking to a low-level component.
Iterator Refactoring. Generic diagram You know this one well: the Java collections all implement an Iterator interface. Key benefit: it hides the underling kind of collection since its irrelevant to users just iterating over it. Iterators need to hold the state of progress of one iteration through the object, so you make a new one of these guys for each iteration through the collection.
The take-home message here is you can implement Iterator on your own classes which you may need to iterate through -- e. Composite Refactoring.
Composite lets clients treat individual objects and compositions of objects uniformly. Generic diagram If you needed a recursive union type in C, use the composite pattern in an OO language -- Composite is important! HFDPS Example: restaurant menus with submenus and the solution using a Composite The key advantage of this pattern is how print can be implemented: an individual item just prints itself, and the composite prints all of its components.
Notice how the common superclass MenuComponent has all the methods of an individual MenuItem as well as of a composite Menu.
MenuItem 's add and Menu 's isVegetarian but is needed for the useful uniformity. Swing implements a variation on Composite: JComponent is a subclass of Container , and so JComponent and all its subclasses i. State Refactoring. The object will appear to change its class. Generic diagram Book example is a gumball machine The actions of inserting a coin, turning crank, etc vary depending on the state of the machine coin previously inserted etc aside: behind every state pattern is a finite-state automaton The smelly way to do it -- a bunch of switch or if-then-else statements.
Another Example: in Fowler Refactoring Chapter 1, the state pattern was used for movies because their classification could dynamically change a new class Price was introduced which is the State above, and it had subclasses RegularPrice , etc; Movie is the Context above, holding the Price state: See this Figure.
State is great: the underlying states of the design now have clear reifications as class names. Strategy Refactoring. Strategy lets the algorithm vary independently from clients that use it. This is very similar to State , it supports dynamic changing of some aspects of a class--in this case an algorithm. The class diagram is identical as well. Singleton Refactoring. Generic diagram For a class with only one member, something quite common in practice. Code it so that multiple instances can't be created.
Active 8 years, 5 months ago. Viewed 5k times. Thanks and regards! Improve this question. Tim Tim 1. Add a comment. Active Oldest Votes. Improve this answer. Robert Harvey Robert Harvey k 44 44 gold badges silver badges bronze badges. Wow - that's denser than the GoF. Both links are dead. These are not: arxiv. As can be seen by the other answers to this question, design patterns exist outside of OOP Community Bot 1 1 1 silver badge.
Oded Oded k 96 96 gold badges silver badges bronze badges. Gant Gant Absolutely not. It doesn't have to be tied to object-orientation OOP.
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