GoF Design Patterns
Simple implementations of GoF Design Patterns.
Intention of the current repository is to collect the implementations of the patterns presented in the Gang of Four book through easy (dummy) examples.
Patterns are not miexed to work together as it would be in a real life situation like Strategy is commonly used with Factory and so on. The intention is to understand the key ideas behind the scenes. That is the reason why Generics, Collections, Reflection API or the other powerful Java tools and language features are tried to be avoided to let focus on the structure of the patterns themselves.
Eclipse is used for implementation hence DesignPatterns direcory can be imported to an Eclipse workspace. EGit can be used however it is not necessary at all.
In the default package DesignPatterns/src/ there will be Main*.java named files (so called wrappers for each
of the patterns) and in Eclips pick one, right-click on it and Run As > Java Application will execute it
(and check out the Console tab for output).
The language is used: Java
The UML diagram collection is available here: GoF Design Pattern UMLs.
List of GoF patterns by types
Creational
Creational patterns are ones that create objects for you, rather than having you instantiate objects directly. This gives your program more flexibility in deciding which objects need to be created for a given case.
- Abstract Factory groups object factories that have a common theme.
- Builder constructs complex objects by separating construction and representation.
- Factory Method creates objects without specifying the exact class to create.
- Prototype creates objects by cloning an existing object.
- Singleton restricts object creation for a class to only one instance.
Structural
These concern class and object composition. They use inheritance to compose interfaces and define ways to compose objects to obtain new functionality.
- Adapter allows classes with incompatible interfaces to work together by wrapping its own interface around that of an already existing class.
- Bridge decouples an abstraction from its implementation so that the two can vary independently.
- Composite composes zero-or-more similar objects so that they can be manipulated as one object.
- Decorator dynamically adds/overrides behaviour in an existing method of an object.
- Facade provides a simplified interface to a large body of code.
- Flyweight reduces the cost of creating and manipulating a large number of similar objects.
- Proxy provides a placeholder for another object to control access, reduce cost, and reduce complexity.
Behavioral
Most of these design patterns are specifically concerned with communication between objects.
- 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 (undo).
- 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 runtime.
- Template Method defines the skeleton of an algorithm as an abstract class, allowing its subclasses to provide concrete behavior.
- Visitor separates an algorithm from an object structure by moving the hierarchy of methods into one object.
Further Plans
Non-GoF Patterns
Non- Gang of Four patterns will be implemented later.
Analysis and Application of Patterns
Analysis, use case studies will be available later with pros and cons about application of Design Patterns to cooperate with each other and hints on how to use them to create a coherent and reusable implementations.
Ideas are welcomed of course!