Choose a pattern for a problem
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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.
Choose a pattern for a problem
- 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