Welcome to Design Patterns in Java 👋

This repository is part of the Refactoring.Guru project.

It contains Java examples for all classic GoF design patterns.

Requirements

The examples were written in Java 8, but also tested in Java 9.

For the best experience, we recommend working with examples in IntelliJ IDEA. The Community Edition of IDE is available for free (https://www.jetbrains.com/idea/download/).

After downloading or cloning this repository to your computer, import its root directory into a New project:

• Either through start dialog: Select "Import Project" option and skip through the rest of the steps.

• Or via the main menu: File > New > Project from Existing Sources...

After importing the project, you will be able to run examples by right-clicking "Demo" files inside every example and selecting the "Run" command from the context menu.

Roadmap

• Add detailed comments all classes.
• Add structure-only examples.

Design Patterns Implemented

Structural

• UML – Class Adapter — allows classes with incompatible interfaces to work together by wrapping its own interface around that of an already existing class
• UML – Object Adapter
• UML – Facade — provides a simplified interface to a large body of code
• UML – Composite — composes zero-or-more similar objects so that they can be manipulated as one object
• UML – Decorator — dynamically adds/overrides behaviour in an existing method of an object
• UML – Proxy — provides a placeholder for another object to control access, reduce cost, and reduce complexity
• UML – Flyweight — reduces the cost of creating and manipulating a large number of similar objects
• UML – Bridge — decouples an abstraction from its implementation so that the two can vary independently

Creational

• UML – Factory Method — creates objects without specifying the exact class to create
• UML – Abstract Factory — groups object factories that have a common theme
• UML – Prototype — creates objects by cloning an existing object
• UML – Singleton — restricts object creation for a class to only one instance
• UML – Builder — constructs complex objects by separating construction and representation

Behavioral

• UML – Template Method — defines the skeleton of an algorithm as an abstract class, allowing its subclasses to provide concrete behavior
• UML – Strategy — allows one of a family of algorithms to be selected on-the-fly at runtime
• UML – State — allows an object to alter its behavior when its internal state changes
• UML – Command — creates objects which encapsulate actions and parameters
• UML – Observer — is a publish/subscribe pattern which allows a number of observer objects to see an event
• UML – Mediator — allows loose coupling between classes by being the only class that has detailed knowledge of their methods
• UML – Memento — provides the ability to restore an object to its previous state (undo)
• UML – Iterator — accesses the elements of an object sequentially without exposing its underlying representation
• UML – Visitor — separates an algorithm from an object structure by moving the hierarchy of methods into one object
• UML – Chain of Responsability — delegates commands to a chain of processing objects

Author

👤 HaYoung Ko

• Github: @edenko
• email: goodeden3@gmail.com

References

Licensed under MIT.