BUILDER, MEDIATOR, AND DECORATOR Team 2 (Eli.SE).

BUILDER, MEDIATOR, AND DECORATOR

Team 2 (Eli.SE)

BUILDER

Builder Pattern

Multiple objects can be constructed with the same interface

Similar to Factory Pattern Focuses on building items step-by-step

Class Diagram

Pizza

Multiple different types, same process Build dough Build sauce Build toppings

PizzaBuilder

abstract class PizzaBuilder {

protected Pizza pizza // has 3 attributes: dough, sauce, toppings

public Pizza getPizza() {

return pizza;

}

public void createNewPizzaProduct() {

pizza = new Pizza();

}

abstract public void buildDough();

abstract public void buildSauce();

abstract public void buildToppings();

}

HawaiianPizzaBuilder

class HawaiianPizzaBuilder extends PizzaBuilder {

public void buildDough() {

pizza.setDough("cross");

}

public void buildSauce() {

pizza.setSauce("mild");

}

public void buildToppings() {

pizza.setToppings("ham+pineapple");

}

}

Cook

class Cook {

private PizzaBuilder pizzaBuilder;

public void setPizzaBuilder(PizzaBuilder pb) {

pizzaBuilder = pb;

}

public Pizza getPizza() {

return pizzaBuilder.getPizza();

}

public void constructPizza() {

pizzaBuilder.createNewPizzaProduct();

pizzaBuilder.buildDough();

pizzaBuilder.buildSauce();

pizzaBuilder.buildToppings();

}

}

BuilderExample

class BuilderExample {

public static void main(String[] args) {

Cook cook = Cook.new();

HawaiianPizzaBuilder hawaiianBuilder = new HawaiianPizzaBuilder();

SpicyPizzaBuilder spicyBuilder = new SpicyPizzaBuilder();

Pizza hawaiianPizza;

Pizza spicyPizza;

cook.setPizzaBuilder(hawaiianBuilder);

cook.constructPizza();

hawaiianPizza = cook.getPizza();

cook.setPizzaBuilder(spicyBuilder);

cook.constructPizza();

spicyPizza = cook.getPizza();

}

}

Why this over factory pattern? Individual steps may not be used

Hold the pickles, extra mustard

Sources

http://en.wikipedia.org/wiki/Builder_pattern

http://sourcemaking.com/design_patterns/builder

MEDIATOR DESIGN PATTERN

Overview of Mediator

Defines an object that manages how a set of objects interact

Objects interact with the mediator object rather than with each other

Real World Example

Diagram

Advantages

Reduces coupling in situations when many objects need to communicate

Minimizes “spaghetti code” by localizing the communication process to just one class

Disadvantages

Easy for mediators to become complex in practice

DECORATOR PATTERN

Raul Aragonez

Intent

Attach additional responsibilities to an object dynamically.

Decorators provide a flexible alternative to subclassing for extending functionality.

Client-specified embellishment of a core object by recursively wrapping it.

UML Diagram

Participants

Component: defines the interface for objects that can have responsibilities added to them dynamically.

Concrete Component: is the object that can be decorated. It is defined so that zero or more responsibilities can be attached to it.

Decorator: maintains a reference to a Component object an interface that conforms to Component's interface.

Concrete Decorator: wraps around the Concrete Component and adds functionality to it.

Pizza Example

Class Explosion

Instead…

Advantages

Responsibilities can be added to one object without affecting the rest of the objects in the class.

Contents of the object are not affected and Responsibilities can be removed as easily as they are added.

Lots of Features = slow system performance = unnecessary code we need to support. We are paying for features that we don't need!

Therefore, Decorator lets us add features and responsibilities as we need them at run-time.

Pizza example Renovation

Lets try it!

Disadvantages

Lots of little objects  As a system gets larger it would become

composed of many little objects that look the same, decorator objects. This makes it hard to learn the system and debug the code.

Maintenance of the Decorator code when adding functionality to an object, there is no

need to know the interface of the Decorator class. The Decorator must conform to the interface of the object. This means that there's always the need to maintain the interface to keep it synchronized with the object interface.

Sources

http://www.giantflyingsaucer.com/blog/?p=1084

http://sourcemaking.com/design_patterns/decorator

http://oreilly.com/catalog/hfdesignpat/chapter/ch03.pdf

http://pages.cpsc.ucalgary.ca/~jadalow/seng60904/decorator_paper.html#intent