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A design pattern
goes to the supermarket
Kaya Weers
Kaya Weers | Ordina
First, an important question..
Kaya Weers | Ordina
So… Design Patterns?
Design patterns don’t give you code.
They provide general, reusable solutions for the common
problems in software design
Blueprints that you can customize.
Kaya Weers | Ordina
A bit of history
• Book by the Gang of Four (1994)
• 23 patterns, in 3 categories
• Ways to solve problems
• Same vocabulary
Kaya Weers | Ordina
Let me introduce you:
Bobby
Billie
Kaya Weers | Ordina
On a Saturday afternoon..
Kaya Weers | Ordina
When..
Kaya Weers | Ordina
She said:
Kaya Weers | Ordina
So, what’s the pattern?
• Mom wants groceries
• She writes her request on a note: what needs to be
done by who.
• Little sister’s tasks is to bring the note to the table
• Bobby knows how to handle the request on the note
Kaya Weers | Ordina
Command pattern
• Encapsulates request as a stand-alone object
• Decouple trigger from the content request
• Invoker doesn’t need to know content of request
Kaya Weers | Ordina
Command pattern
(client) (invoker) (Command)
(receiver)
Mom Little Sister Note
DoGroceries
Note
Bobby
interface
setCommand(note) execute()
execute()
doGroceries()
Kaya Weers | Ordina
* constructors omitted for readability *
Kaya Weers | Ordina
10 minutes later..
Kaya Weers | Ordina
They cannot find the coffee
Kaya Weers | Ordina
“Sigh…“
Kaya Weers | Ordina
So, what’s the pattern?
• Bobby asks employee when the coffee will be back in
stock
• Employee doesn’t know at that moment
• Employee doesn’t want customers to ask him again
• Customers can sign up to be notified as soon as the
product is available
Kaya Weers | Ordina
Observer pattern
• One-to-many relationship
• When the state from an object changes,
all dependencies are notified
• Loose coupling
Kaya Weers | Ordina
Observer pattern
(subject)
(Observers)
StockUpdate
Bobby
Customer 1
Customer 2
register(observer)
Kaya Weers | Ordina
Observer pattern (Observers)
StockUpdate
Bobby
Customer 1
Customer 2
notifyObservers()
update()
update()
update()
(subject)
Kaya Weers | Ordina
* constructors omitted for readability *
Kaya Weers | Ordina
The next product..
.. is also a challenge
Kaya Weers | Ordina
But, the text is in..
Spanish!
Kaya Weers | Ordina
Luckily, it’s 2024
Kaya Weers | Ordina
So, what’s the pattern?
• Billie wants to read the ingredients
• But Billie can’t read Spanish
• Translation app converts the Spanish words to
English words
• Billie can read English
Kaya Weers | Ordina
Adapter pattern
• Lets classes work together that couldn’t otherwise,
because of incompatible interfaces
• The adapter converts an interface into an interface
that the client expects
• More generic interface
Kaya Weers | Ordina
Adapter pattern
(client) (client interface)
(adapter)
Billie Product
Spanish
Product
Product
Translator
getIngredients()
getIngredients
InSpanish()
getIngredients()
(service)
interface
Kaya Weers | Ordina
* constructors omitted for readability *
Kaya Weers | Ordina
Last on their list..
Kaya Weers | Ordina
They go to the bakery
Kaya Weers | Ordina
They enter the French bakery
Kaya Weers | Ordina
So, what’s the pattern?
• Order supermarket bakery: ‘bread’
• Order French bakery: ‘bread’
• Different result: different variants of bread
• Creation differs per location
Kaya Weers | Ordina
Factory method pattern
• Interface for creating objects in superclass
• Object creation in subclass, can alter the type of
objects
• Easy to extend: add new creator subclasses
Kaya Weers | Ordina
Factory method pattern
Bread
WholeGrain
SlicedBread
interface
Baguette
Bakery
Supermarket
Bakery
createBread()
createBread()
abstract class
French
Bakery
createBread()
factory method
Kaya Weers | Ordina
* constructors omitted for readability *
Kaya Weers | Ordina
The smell of the bakery
.. made them hungry.
Kaya Weers | Ordina
The baker prepares the sandwiches
Kaya Weers | Ordina
The baker follows steps
Kaya Weers | Ordina
So, what’s the pattern?
• Bobby and Billie order two different sandwiches
• The baker creates them with different ingredients
• Most of the steps are the same, easy for baker
• Some steps are optional, like the topping
Kaya Weers | Ordina
Template method pattern
• Superclass defines a skeleton
• Subclasses have specific implementation for steps
• Superclass can contain (default) implementation
Kaya Weers | Ordina
Template method pattern
Sandwich
Chicken
Sandwich
prepare()
addFirstLayer()
addFirstLayer()
abstract class
Vegetable
Sandwich
addFirstLayer()
template method
Kaya Weers | Ordina
* constructors omitted for readability *
Kaya Weers | Ordina
With both their shopping bags and
bellies full..
they go home
Kaya Weers | Ordina
They drop the bag at the floor
Kaya Weers | Ordina
5 min later..
Kaya Weers | Ordina
So, what’s the pattern?
• Mom gives 1 instruction: “put away groceries”
• Bobby and Billie put everything in the right place
• Mom gives no specific instructions
• Mom doesn’t need to know about steps taken
Kaya Weers | Ordina
Facade pattern
• Simplified interface for client
• Client doesn’t need to know about subsystem
• Removes complexity from the interface
Kaya Weers | Ordina
Facade pattern
Bobby
Freezer
putAwayGroceries()
Cabinet Refrigerator Pantry
(client)
Mom
(facade)
Kaya Weers | Ordina
* constructors omitted for readability *
Kaya Weers | Ordina
Summary
Command Observer Adapter
Facade
Template method
Factory method
Kaya Weers | Ordina
Going to the supermarket..
will never be the same again
Kaya Weers | Ordina
THANK YOU
@KayaWeers
/KayaWeers

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Design pattern talk by Kaya Weers - 2024

  • 1. A design pattern goes to the supermarket Kaya Weers
  • 2. Kaya Weers | Ordina First, an important question..
  • 3. Kaya Weers | Ordina So… Design Patterns? Design patterns don’t give you code. They provide general, reusable solutions for the common problems in software design Blueprints that you can customize.
  • 4. Kaya Weers | Ordina A bit of history • Book by the Gang of Four (1994) • 23 patterns, in 3 categories • Ways to solve problems • Same vocabulary
  • 5. Kaya Weers | Ordina Let me introduce you: Bobby Billie
  • 6. Kaya Weers | Ordina On a Saturday afternoon..
  • 7. Kaya Weers | Ordina When..
  • 8. Kaya Weers | Ordina She said:
  • 9. Kaya Weers | Ordina So, what’s the pattern? • Mom wants groceries • She writes her request on a note: what needs to be done by who. • Little sister’s tasks is to bring the note to the table • Bobby knows how to handle the request on the note
  • 10. Kaya Weers | Ordina Command pattern • Encapsulates request as a stand-alone object • Decouple trigger from the content request • Invoker doesn’t need to know content of request
  • 11. Kaya Weers | Ordina Command pattern (client) (invoker) (Command) (receiver) Mom Little Sister Note DoGroceries Note Bobby interface setCommand(note) execute() execute() doGroceries()
  • 12. Kaya Weers | Ordina * constructors omitted for readability *
  • 13. Kaya Weers | Ordina 10 minutes later..
  • 14. Kaya Weers | Ordina They cannot find the coffee
  • 15. Kaya Weers | Ordina “Sigh…“
  • 16. Kaya Weers | Ordina So, what’s the pattern? • Bobby asks employee when the coffee will be back in stock • Employee doesn’t know at that moment • Employee doesn’t want customers to ask him again • Customers can sign up to be notified as soon as the product is available
  • 17. Kaya Weers | Ordina Observer pattern • One-to-many relationship • When the state from an object changes, all dependencies are notified • Loose coupling
  • 18. Kaya Weers | Ordina Observer pattern (subject) (Observers) StockUpdate Bobby Customer 1 Customer 2 register(observer)
  • 19. Kaya Weers | Ordina Observer pattern (Observers) StockUpdate Bobby Customer 1 Customer 2 notifyObservers() update() update() update() (subject)
  • 20. Kaya Weers | Ordina * constructors omitted for readability *
  • 21. Kaya Weers | Ordina The next product.. .. is also a challenge
  • 22. Kaya Weers | Ordina But, the text is in.. Spanish!
  • 23. Kaya Weers | Ordina Luckily, it’s 2024
  • 24. Kaya Weers | Ordina So, what’s the pattern? • Billie wants to read the ingredients • But Billie can’t read Spanish • Translation app converts the Spanish words to English words • Billie can read English
  • 25. Kaya Weers | Ordina Adapter pattern • Lets classes work together that couldn’t otherwise, because of incompatible interfaces • The adapter converts an interface into an interface that the client expects • More generic interface
  • 26. Kaya Weers | Ordina Adapter pattern (client) (client interface) (adapter) Billie Product Spanish Product Product Translator getIngredients() getIngredients InSpanish() getIngredients() (service) interface
  • 27. Kaya Weers | Ordina * constructors omitted for readability *
  • 28. Kaya Weers | Ordina Last on their list..
  • 29. Kaya Weers | Ordina They go to the bakery
  • 30. Kaya Weers | Ordina They enter the French bakery
  • 31. Kaya Weers | Ordina So, what’s the pattern? • Order supermarket bakery: ‘bread’ • Order French bakery: ‘bread’ • Different result: different variants of bread • Creation differs per location
  • 32. Kaya Weers | Ordina Factory method pattern • Interface for creating objects in superclass • Object creation in subclass, can alter the type of objects • Easy to extend: add new creator subclasses
  • 33. Kaya Weers | Ordina Factory method pattern Bread WholeGrain SlicedBread interface Baguette Bakery Supermarket Bakery createBread() createBread() abstract class French Bakery createBread() factory method
  • 34. Kaya Weers | Ordina * constructors omitted for readability *
  • 35. Kaya Weers | Ordina The smell of the bakery .. made them hungry.
  • 36. Kaya Weers | Ordina The baker prepares the sandwiches
  • 37. Kaya Weers | Ordina The baker follows steps
  • 38. Kaya Weers | Ordina So, what’s the pattern? • Bobby and Billie order two different sandwiches • The baker creates them with different ingredients • Most of the steps are the same, easy for baker • Some steps are optional, like the topping
  • 39. Kaya Weers | Ordina Template method pattern • Superclass defines a skeleton • Subclasses have specific implementation for steps • Superclass can contain (default) implementation
  • 40. Kaya Weers | Ordina Template method pattern Sandwich Chicken Sandwich prepare() addFirstLayer() addFirstLayer() abstract class Vegetable Sandwich addFirstLayer() template method
  • 41. Kaya Weers | Ordina * constructors omitted for readability *
  • 42. Kaya Weers | Ordina With both their shopping bags and bellies full.. they go home
  • 43. Kaya Weers | Ordina They drop the bag at the floor
  • 44. Kaya Weers | Ordina 5 min later..
  • 45. Kaya Weers | Ordina So, what’s the pattern? • Mom gives 1 instruction: “put away groceries” • Bobby and Billie put everything in the right place • Mom gives no specific instructions • Mom doesn’t need to know about steps taken
  • 46. Kaya Weers | Ordina Facade pattern • Simplified interface for client • Client doesn’t need to know about subsystem • Removes complexity from the interface
  • 47. Kaya Weers | Ordina Facade pattern Bobby Freezer putAwayGroceries() Cabinet Refrigerator Pantry (client) Mom (facade)
  • 48. Kaya Weers | Ordina * constructors omitted for readability *
  • 49. Kaya Weers | Ordina Summary Command Observer Adapter Facade Template method Factory method
  • 50. Kaya Weers | Ordina Going to the supermarket.. will never be the same again
  • 51. Kaya Weers | Ordina THANK YOU @KayaWeers /KayaWeers