design-patterns

This repository contains a bunch of simple design patterns examples.

Mediator

Event-driven chat-room implementations Every user can send a message to the ChatBox, which then broadcasts it to the remaining users.

Chain Of Responsibility

Simulator of an ATM that accepts an amount in dollars and in cents and then prints out the minimum number of bills / coins and their respective values needed to match the given amount.

Builder

A scalable tool allowing the user to create reports of different types: XML reports and JSON reports. The user may also specify what information needs to be included in the report.

Composite

A program used to send notifications to customers. Each customer can either be "simple", meaning a physical person with an inbox, or "composite", that is, composed of a group of simple and/or composite customers. This program wraps each type of customer with a common interface and hides the implementation from the process of sending notifications.

Iterator

This application consists of User objects and ChatRoom objects. Each user can join a nubmer of ChatRooms. Also, users are able to set their global status: visible or hidden. One can only iterate through the users in a chatroom, using special Iterator objects for the specific ChatRoom. The Iterator only caters for visible users.

Singleton

This project consists of a singleton Logger class which caters for writing information to a file and a set of worker classes. The worker classess calculate a certain number of the harmonic series

H_n = 1 + 1/2 + 1/3 + 1/4 + ... + 1/n

and then write information about their execution to a file, using the previously mentioned logger.

NOTICE This implementation of Singleton is not thread safe.

Thread Safe Singleton

The ConsoleLogger is a singleton class, which stores a counter and can log its value, together with the hash of the current object instance, to the console. Multiple threads are fetching an instance of the logger and calling its method. Because of enhanced singleton constructor (prior to the previous example) only one instance is ever created.

Adapter

We have an existing interface ISquare which provides two methods: GetArea() and GetPerimeter(). We need to work with a legacy class StrangeSquare with one method: GetDiagonal(). An adapter is used to match the interface of the square with IShape.

Decorator

We have a class responsible of processing and displaying messages: MessageChannel. This example provides an interface for extending (decorating) the message preparation process. TrimmedMessageChannel and CensoredMessageChannel augment the way messages are processed. Because of applied layers of abstraction, it is easy to add more decorator implementations.

State

This application is a simulation of a simple ATM which can function in any of these states: NoCard, CardEntered. PINEnterd, NoMoney. Depending on the current state of the ATM object, its behavior changes respectively. Different operations are allowed and are implemented in a different way.

Command

A simple GUI application written in WPF. The application features a label and two TextBoxes. The user can interfere with the way that the text is displayed as in the label in question by altering the TextBoxes and clicking their respective buttons. Each action is implemented using the Command design pattern. That way, different request may be passed to different buttons under the same interface: ICommand. This means that the high level module needs no knowledge of implementation details. What is more, every action can be undone, as well as redone.

eryktr/design-patterns