This document summarizes an Agile Saturday event focused on design patterns. It introduces common pattern types and examples like Decorator, Strategy, and Factory. It then presents 8 problems that could benefit from patterns, such as allowing custom pizza orders or multi-volume file decompression. The document promotes extreme programming and invites attendees to consider jobs at Codeborne.

1. Agile Saturday VI
Choose a pattern
for a problem!
Anton Keks
anton@codeborne.com

2. The Increasing Complexity
Complexity of software systems
Time
New programming paradigms
Higher level of abstraction
HW Assembler Structural (objects+functions?)
CPUs Procedural <OOP> ...

3. What are design patterns?
●
Anywhere in the world you can find recurring
patterns
● Design patterns
– are building blocks of a system's
architecture
– are recurring solutions to design problems
that you see over
– identify and specify abstractions that are
above the level of single classes and
instances

4. Pattern classification
The GOF book defines 3 major types of patterns:
– Creational patterns – substitute the new keyword. This
gives your program more flexibility in deciding which
objects need to be created for a given case
– Structural patterns - compose groups of objects into
larger structures, such as complex user interfaces or
accounting data
– Behavioral patterns - define the communication
between objects and how the flow is controlled in a
complex program.

5. Decorator
Adapter
Composite Strategy
State
Observer
Factory
Iterator
Builder
Prototype

6. Software Design: The Good
●
Loose coupling
●
Immutability
●
Encapsulation
● Short code blocks
● Appropriate typing
●
Duplication avoidance
● Simplicity
●
Consistent terminology
● Clear naming

7. Bad, bad, bad!
●
Loose coupling Tight coupling
●
Immutability Mutable data structures
●
Encapsulation Tramp data
● Short code blocks Monster functions/methods
● Appropriate typing String/Integer overuse
●
Duplication avoidance Copy-Paste
● Simplicity Over-engineering
●
Consistent terminology Mixture of terms
● Clear naming Runtime surprises

8. Let's get to business!
● Next slides describe problems
– What is given
(existing code)
– What we want to achieve
(using a pattern)
●
As usual, the code is on github:
http://github.com/angryziber/patterns

9. Problem 1: Pizza
●
We have:
– A pizzeria
– Multitude of options for pizzas: name, toppings,
thickness, size, delivery address, etc
● We want:
– Allow users to “order” custom pizzas
– Disallow changing the order once the pizza is
already in the oven
– Keep the ordering code readable

10. Problem 2: Unzipper
●
We have:
– unzip() method
– It is able to decompress a single compressed
stream
● We need:
– Support multiple-volume archives
– Compressed data is split into multiple floppies

11. Problem 3: Maps
●
We have:
– Map data of entire Tallinn with all the streets,
buildings, etc
– The MapVisualizer class that can draw the full map
on the screen
●
We want:
– User to see only a section of the map at any given
time
– User to be able to move around the map

12. Problem 4: CD Player
●
We have:
– A CD player with buttons play, stop, next, eject
●
We want:
– Play to switch the player on
– Play again to pause playback, again to resume
– Stop to turn off the player
– Eject to open the disk tray (if no disk – no playback
possible)
– etc, etc, etc

13. Problem 5: Vending Machine
●
We have:
– A vending machine that can sell any small enough
items
●
We want:
– To deploy several such machines selling bottles of
pepsi, sushi boxes, and Hintai magazines
– Each machine to sell items of one type

14. Problem 6: Spreadsheet
●
We have:
– A spreadsheet-type program
– Containing a table for entering data and formulas
● We want:
– The program to support charts
– The charts to be updated automatically if user
changes the data in the table
– To sell the chart add-on separately for only $99.99

15. Problem 7: Battlefield
●
We have:
– A tank
– Several types of bullets
– Lots of enemies around, e.g. airplanes, other
tanks, guys with Molotov-coctails
●
We want:
– To survive
– To kill 'em all

16. Problem 8: TCP over DNS
●
We have:
– A paid Wi-Fi network (e.g. in an airport)
– Lots of spare time, but no credit card
● We want:
– To be able to read emails and surf Facebook
– (Most likely, during our next trip)
● Background info:
– Paid Wi-Fi usually resolves DNS just fine
– DNS packets can contain any payload

17. Thank you!
Codeborne is the only true extreme
programming company in the region.
Come and join us for an experience of
a lifetime you can't find elsewhere!
job@codeborne.com