[PDF] Lecture: Design Patterns - UZH





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96 Part III • Design Patterns The Facade Pattern: Key Features Intent You want to simplify how to use an existing system You need to define your own interface Problem You need to use only a subset of a complex system Or you need to in-teract with the system in a particular way

Who are the key participants in the design pattern?

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What are the elements of a design pattern?

In general, a pattern has four essential elements: Design Patterns: Elements of Reusable Object-Oriented Software 13 1. The pattern nameis a handle we can use to describe a design problem, its solutions, and consequences in a word or two.

What is within participant designs?

Within participant designs Module: Research Methods in Psychology (PS1813) ??Within participant designs oEach does both conditions - allows you to have fewer participants, more powerful for given sample size oPeople act as own control group but there may be order, practice and fatigue effects

How many participants are followed in a design?

2 In a design one group of participants is followed and assessed as the group from PSY 101 at Ateneo de Manila University Study Resources Main Menu by School by Literature Title by Subject by Study Guides Textbook SolutionsExpert TutorsEarn Main Menu Earn Free Access Upload Documents Refer Your Friends Earn Money Become a Tutor Scholarships

Software Engineering

Lecture: Design Patterns

Thomas Fritz & Martin Glinz

Many thanks to Philippe Beaudoin, Gail

Murphy, David Shepherd, Neil Ernst and

Meghan Allen

Reading!

For this lecture: (all required)

"Composite Design Pattern "Mediator Design Pattern "Facade Design Pattern 2 3

Design Patterns Overview

"Introduction to design patterns "How to use design patterns "Components of a pattern "Various patterns

‰Creational

‰Structural

‰Behavioral

"Integrating Patterns

Learning Goals

By the end of this unit, you will be able to:

"Explain why design patterns are useful and some caveats to consider when using design patterns "Clearly and concisely describe, give examples the key benefit of, and drawbacks or special considerations for the following patterns: abstract factory, singleton, façade, composite, decorator and observer 4

Software Updates

5

Design Challenges

"Designing software with good modularity is hard! "Designs often emerge from a lot of trial and error

Are there solutions to common recurring

problems? 6

Design Patterns

In software engineering, a design pattern is a

general repeatable solution to a commonly occurring problem in software design. "A design pattern is a description or template for how to solve a problem "Not a finished design "Patterns capture design expertise and allow that expertise to be transferred and reused "Patterns provide common design vocabulary, improve communication, ease implementation & documentation 7 8

Real World Pattern Examples

"Problem: sink stinks "Pattern:

S-trap

"Problem: highway crossing "Pattern: clover leaf 9

Updates ² Observer Design Pattern

Name: Observer

Intent: Ensure that, when an object changes state, all its dependents are notified and updated automatically.

Participants & Structure:

Updates ² Observer Design Pattern

10

Software

(subject)

Client A

Client B

Client C

Clients

(Observers)

Attach()

Updates ² Observer Design Pattern

11

Software

(subject)

Client A

Client B

Client C

Clients

(Observers)

Update()

Updates ² Observer Design Pattern

12

Software

(subject)

Client A

Client B

Client C

Clients

(Observers)

Update()

O B S E R V E R

Use common

Observer interface

13

2NVHUYHU G3 ŃRQP·G

"I need the professor to be notified when a student joins his/her class "I want the display to update when the size of a window is changed "I need the schedule view to update when the database is changed

Design patterns are reusable!

Real world example

Newspaper subscriptions

"The newspaper company publishes newspapers. "You subscribe to a particular paper, and every "At some point in the future, you can unsubscribe "While the newspaper company is in business, people, hotels and other businesses constantly subscribe and unsubscribe to the newspaper. example from Head First Design Patterns 14 In this example, who is the Observer and who is the Subject? 15

How to use Design Patterns?

‰Know the patterns

‰Know the problem they can solve

‰Recognize when a problem is solvable by a pattern

‰Look up the pattern

‰Correctly integrate it into your code

16

Knowing the patterns helps

understanding code "The pattern sometimes convey a lot of information "Try understanding this code: "Key is to know the Abstract Factory and Decorator patterns!

Design patterns also provide a shared

vocabulary. of all of its listeners and anytime it has new data it sends a message to each listener. The listeners can join the Broadcast at any time or really dynamic and loosely- example from Head First Design Patterns 17 18

Components of a pattern

"Pattern Name "Intent

‰What problem does it solve?

"Participants

‰What classes participate

"These classes usually have very general names, the pattern is meant to be used in many situations! "Structure

‰How are the classes organized?

‰How do they collaborate?

19

A Menagerie of Patterns!

20

Pattern Classifications

Creational Patterns

‰Makes a system independent of how its object are created ‰Useful as system evolve: the classes that will be used in the future may not be known now

Structural Patterns

‰Techniques to compose objects to form larger

structures

Behavioral Patterns

‰Concerned with communication between objects

‰Describe complex control flow

21

Discussion Question

"What is the Classification of the Observer pattern?

‰Creational, Structural, Behavioural?

Observer Pattern

"Consider your projects. What classes could be an observer or a subject? 22
23

Behavioral Patterns

"Mediator "Observer "Chain of Responsibility "Command "Interpreter "Iterator "Memento "State "Strategy "Template Method "Visitor 24

Creational Patterns

"Abstract Factory "Singleton "Builder "Factory Method "Prototype

Design problem

"Build a maze for a computer game "A maze is a set of rooms "A room knows its neighbours: room, door, wall "Ignore players, movement, etc. 25

MazeGame

CreateMaze()

26

Exercise

1.Implement the function

MazeGame:CreateMaze() to design a maze

with 2 rooms and a connecting door.

2.Update that function to make a Maze

containing a Room with a bomb in it. 27

Example

// in the class MazeGame public Maze createMaze() {quotesdbs_dbs4.pdfusesText_7
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