ubb.dp.1819

UBB Design Patterns repository for university year 2018-2019

Grading criteria

1. Course presentations during the semster: 50% of final grade

2. Lab presentations at the end of the semester:

2.1. Identify from open-source project ( https://github.com/trending?since=daily ) OR use in B.A. Thesis, 2 patterns from each category (60% of lab grade):

• Creational (except Singleton)

• Structural

• Behavioral

2.2. Question from 1-2 basic patterns (Creational, Structural or Behavioral) (40% of lab grade)

2.3. Bonus max 1p: Question from 1 Arhitectural or Enterprise pattern

2.4. Bonus max 1p: All lab assignments done and merge requests made for each

Git commands to update from remote repo

git remote add upstream https://github.com/lzrmihnea/ubb.dp.1819

git fetch upstream

git pull upstream master

Lecture Notes

Introduction to Course

http://www.cs.ubbcluj.ro/~arthur/dp2018/00.Introduction%20to%20Course.pdf

OOP Recap. SOLID Principles

http://www.cs.ubbcluj.ro/~arthur/dp2018/01.Recap.%20SOLID%20Principles.pdf

Creational Patterns

http://www.cs.ubbcluj.ro/~arthur/dp2018/02.Creational%20Patterns.pdf

Structural Patterns

http://www.cs.ubbcluj.ro/~arthur/dp2018/03.Structural%20Patterns.pdf

Behavioural Patterns

http://www.cs.ubbcluj.ro/~arthur/dp2018/04.Behavioural%20Patterns.pdf

Architectural Patterns

http://www.cs.ubbcluj.ro/~arthur/dp2018/05.Architectural%20Patterns.pdf

Laboratories

Lab 1. Creational Patterns

• Singleton
• Factory
• Builder
• Prototype

Ex. 1.1. Encapsulation

We will want to read information from a file and interpret this information via a Service. Using the Single-Responsibility principle from SOLID, please create 2 Services:

• The first Service reads a file and returns all lines in the file in a List of Strings

• The second Service interprets this data as coffee ingredients

-- a line containing only 3 or 4 words is a valid ingredients line. Fewer or more words are invalid.

-- of the 3 or 4 words:

--- one should be a quantity (200)

--- one should be a unit (ml)

--- one should be an ingredient (milk)

--- the last one is optional and should be an adjective (boiled, steamed, roasted, etc.)

Ex. 1.2. Coffee Factory

Create a Coffee Service implementation to return an identified coffee type depending on the ingredients given as input

The list of possible coffee types:

• espresso: 2 cups water + 0.25 cups coffee-beans roasted
• cappuccino: 2 cups water + 0.25 cups coffee-beans roasted + 100ml foamed milk
• americano: 4 cups water + 0.25 cups coffee-beans roasted
• add a coffee of your choosing with name and ingredients

Ex. 1.3. Coffee Builder

Encapsulate the creation of the coffee with each line of ingredients with a builder.

Lab 2. Structural Patterns

• Adapter
• Bridge
• Composite
• Decorator
• Facade

Ex 2.1. Adapter
Adapt the Service which reads coffee ingredients from a file to read Car Parts

• 4 summer wheels (can be summer or winter)
• 1 titanium chassis (can be titanium, aluminium, vibranium or adamantium)
• 1 electric engine (can be electric, diesel or GPL)
• 1 red paint (can be red, white, black, blue, pink, green, yellow)

Ex 2.2. Bridge Create a Service which, depending on the given car parts, creates a car with the given components

• use the classes given in the Examples package (to be added on 15.03.2019-18.03.2019)
• print to the output how that car would look like

Ex 2.3. Composite Create a basic PriceComposite, which has as leaves basic components. Define in the Component if the Leaf has a Fixed Price or a calculated Price. All basic car parts will have Fixed prices. Only the Car root element will have a Computed Price. This will be calculated on request via a method invocation on the Composite root, which, if the Price is fixed, returns the direct Price of the Component, if the Price should be computed, sums up the Prices of the Leaves.

Ex 2.4 Proxy Around the Service which creates the car, create a Proxy service, which prints all car creations, along with their costs.

Ex 2.5 Decorator Add CarDecorations, extending the Car class. Adapt the CarPricingComposite to take a common (different) Interface, such as the CarPriceable, which can have in its leaves both Car Components and Car Decorations. The Car decorations do not add functionality, only cost (The Paint will remain a Component, despite not necessarily adding real-world functionality).

The classes are purposefully ambiguous and some Interfaces are purposefully not used in classes. See which are better suited for which uses of our exercises.

Ask your teachers if the instructions are unclear.

Lab 3. Behavioral patterns (Command, Mediator, Observer)

Chess pieces:

• peon ( 1 square forward movement )
• horse ( L movement )
• bishop ( diagonal movement )

each piece having

• a current position (vert, horiz)
• isAlive
• color (black, white)

Ex. 3.1. Command pattern

Create movement command classes for each movement

• peon basic move ( 1 forward )
• horse L movement
• bishop diagonal movement

Create attack command class:

• attack movement(fromPiece, toPiece)

Ex. 3.2. Mediator pattern

Create a Board (Mediator) with dimensions which takes a list of pieces, with positions along with their actions:

The Mediator has always the list of where each piece is

Each movement of a piece is checked to see if there is already a piece there.

• piece1 move => Mediator checks if there is another piece already there, invokes attack action if there is
• piece1 move => same thing
• piece2 move => same thing

Ex. 3.3. Observer pattern

Observer : interface

• KillCounterObserver - counts kills
• PrintObserver - simply prints

Add to the mediator a list of Observers (abstract)

Call the observer list each time an attack appears

Add a third Observer, to your choice

Lab 4. Behavioral patterns II (State, Chain of Responsibility, Strategy)

Ex. 4.1. State

Given a company with 3 types of Employees (Project Manager, Team Leader, Developer) and 3 possible billable day statuses (holiday, sick leave, working, home office, unpaid leave).

1. Using the State pattern implement the behavior for each type of day.
2. Take into consideration that based on billable day type the paycheck will differ
3. Add state attribute for billable amount information for employee (each employee has a different paycheck)

Ex. 4.2. Chain of responsibility

Given the following:

• employees can go on various leave types holiday, sick leave, home office, unpaid leave
• leave days need to be approved
• the Project Manager needs to approve first, if the Project Manager is missing the Team Leader can approve instead of the Project Manager

Using the Chain of Responsibility pattern implement the leave day approval system.

Ex. 4.3. Strategy

Given the fact that employees need to be notified about leave day approval or rejection and that there are 3 official ways of communication in the company (SMS, Push Notification and Email). Using the Strategy pattern implement the behavior required for a holiday approver to notify each Employee in the chosen communication way.

Lab 5. Enterprise integration patterns

Download RabbitMQ and run the service locally.

Tutorials - Code Samples

Ex. 5.1 Producer/Consumer

We have a mail client and we've noticed that sending emails is currently taking a long time (1sec). We need to decouple the sending of emails using a message broker (e.g. RabbitMQ) and ensure that we can process the messages asynchronously and with multiple consumers (workers) in parallel.

Ex. 5.2 Publish/Subscribe

Our current notification system has to send notifications via Email, PushNotifications and SMS Notifications. Currently each taken individually takes a long time to execute and we have to send the exact same message if the user has all of them configured.

Using a message broker implement a publish/subscribe mechanism that can receive messages and distribute them to all connected notification subscribers.

Ex. 5.3 Topic

We have an email sending service that is responsible for sending emails to customers across the world. Due to GDPR constraints we need to ensure that emails from each region are treated independently (e.g. USA, Europe etc.).

Using a topic based message broker write a client that can send emails to their corresponding topic and implement consumers for each topic.