public/subjects/java/piscine/Decorator

Decorator

Instructions

Now let's implement the Decorator Design Pattern

classDiagram
class Raclette {
    <<interface>>
    +getCalories()* int
    +getIngredients()* String 
}
class BaseRaclette {
    +getCalories() int
    +getIngredients() String
}
class RacletteDecorator {
    <<abstract>>
    -Raclette raclette
    +RacletteDecorator(Raclette raclette)
    +getCalories() int
    +getIngredients() String
}
class WithPickles {
    -Raclette raclette
    +RacletteDecorator(Raclette raclette)
    +getCalories() int
    +getIngredients() String
}
class WithColdMeats {
    -Raclette decoratedRaclette
    +RacletteDecorator(Raclette raclette)
    +getCalories() int
    +getIngredients() String
}

Raclette <|.. BaseRaclette
Raclette <|.. RacletteDecorator
RacletteDecorator <|-- WithPickles
RacletteDecorator <|-- WithColdMeats

Here is the matching class diagram. Create the matching classes in the matching files.

Here is the description :

• BaseRaclette :
  • getCalories should return 1000
  • getIngredients should return "Patate, fromage à raclette"
• RacletteDecorator :
  • getCalories should return the getCalories of the decoratedRaclette attribute
  • getIngredients should return the getIngredients of the decoratedRaclette attribute
• WithPickles :
  • getCalories should return the addition of 50 and the getCalories of the decoratedRaclette attribute
  • getIngredients should return the concatenation of getIngredients of the decoratedRaclette attribute and ", cornichons"
• WithColdMeats :
  • getCalories should return the addition of 350 and the getCalories of the decoratedRaclette attribute
  • getIngredients should return the concatenation of getIngredients of the decoratedRaclette attribute and ", charcuterie"

For each class, implement the toString method to return "getIngredients() pour getCalories() calories".

Usage

Here is a possible ExerciseRunner.java to test your function :

public class ExerciseRunner {

    public static void main(String[] args)  {
        Raclette r = new BaseRaclette();
        System.out.println(r);
        r = new WithPickles(r);
        System.out.println(r);
        r = new WithColdMeats(r);
        System.out.println(r);
    }
}

and its output :

$ javac *.java -d build
$ java -cp build ExerciseRunner 
Patate, fromage à raclette pour 1000 calories
Patate, fromage à raclette, cornichons pour 1050 calories
Patate, fromage à raclette, cornichons, charcuterie pour 1400 calories
$

Notions

Class diagram