Factory Method Pattern

Factory Pattern
Duck duck;
if (picnic) {
duck = new MallardDuck();
} else if (hunting) {
duck = new DecoyDuck();
} else if (inBathTub) {
duck = new RubberDuck();
}

Factory Pattern(Contd.)
Pizza orderPizza(String type) {
Pizza pizza;
if (type.equals(“cheese”)) {
pizza = new CheesePizza();
}
else if (type.equals(“greek”) {
pizza = new GreekPizza();
}
else if (type.equals(“pepperoni”)
{
pizza = new PepperoniPizza();
}
pizza.prepare();
pizza.bake();
pizza.cut();
pizza.box();
return pizza;
}

Factory Pattern (Contd.)
public class SimplePizzaFactory {
public Pizza createPizza(String type) {
Pizza pizza = null;
pizza = new CheesePizza();
} else if (type.equals(“pepperoni”)) {
pizza = new PepperoniPizza();
}
else if (type.equals(“clam”)) {
pizza = new ClamPizza();
}
else if (type.equals(“veggie”)) {
pizza = new VeggiePizza();
}
return pizza;
}
}

public class PizzaStore {
SimplePizzaFactory factory;
public PizzaStore(SimplePizzaFactory
factory) {
this.factory = factory;
}
public Pizza orderPizza(String type) {
Pizza pizza;
pizza = factory.createPizza(type);
pizza.prepare();
pizza.bake();
pizza.cut();
pizza.box();
return pizza;
}
// other methods here
}

NYPizzaFactory nyFactory = new NYPizzaFactory();
PizzaStore nyStore = new PizzaStore(nyFactory);
nyStore.order(“Veggie”);
ChicagoPizzaFactory chicagoFactory = new ChicagoPizzaFactory();
PizzaStore chicagoStore = new PizzaStore(chicagoFactory);
chicagoStore.order(“Veggie”);

public abstract class PizzaStore {
public Pizza orderPizza(String type) {
Pizza pizza;
pizza = createPizza(type);
pizza.prepare();
pizza.bake();
pizza.cut();
pizza.box();
return pizza;
}
protected abstract Pizza createPizza(String type);
}

public class NYStylePizzaStore extends PizzaStore {
public Pizza createPizza(type) {
pizza = new NYStyleCheesePizza();
} else if (type.equals(“pepperoni”) {
pizza = new NYStylePepperoniPizza();
} else if (type.equals(“clam”) {
pizza = new NYStyleClamPizza();
} else if (type.equals(“veggie”) {
pizza = new NYStyleVeggiePizza();
}
}
}

public class ChicagoStylePizzaStore extends PizzaStore {
public Pizza createPizza(type) {
pizza = new ChicagoStyleCheesePizza();
} else if (type.equals(“pepperoni”) {
pizza = new ChicagoStylePepperoniPizza();
} else if (type.equals(“clam”) {
pizza = new ChicagoStyleClamPizza();
} else if (type.equals(“veggie”) {
pizza = new ChicagoStyleVeggiePizza();
}
}
}

public abstract class Pizza {
String name;
String dough;
String sauce;
ArrayList<String> toppings = new
ArrayList<String>();
void prepare() {
System.out.println(name);
System.out.println(“dough...”);
System.out.println(“sauce...”);
System.out.println(“toppings:“);
for (int i = 0; i < toppings.size(); i++)
{
System.out.println(“ “ +
toppings.get(i));
}
}
void bake() {
System.out.println(“Bake”);
}
void cut() {
System.out.println(“Cutting slices”);
}
void box() {
System.out.println(“box”);
}
public String getName() {
return name;
}
}

public class NYStyleCheesePizza extends
Pizza {
public NYStyleCheesePizza() {
name = “NY Style SCheese Pizza”;
dough = “Thin Crust Dough”;
sauce = “Marinara Sauce”;
toppings.add(“Grated Reggiano
Cheese”);
}
}
public class ChicagoStyleCheesePizza
extends Pizza {
public ChicagoStyleCheesePizza() {
name = “Chicago Cheese Pizza”;
dough = “Extra Thick Crust Dough”;
sauce = “Plum Tomato Sauce”;
toppings.add(“Cheese”);
}
void cut() {
System.out.println(“Cutting slices”);
}
}

public class PizzaTestDrive {
public static void main(String[] args) {
PizzaStore nyStore = new NYPizzaStore();
PizzaStore chicagoStore = new ChicagoPizzaStore();
Pizza pizza = nyStore.orderPizza(“cheese”);
System.out.println(“Ethan ordered a “ + pizza.getName() + “n”);
pizza = chicagoStore.orderPizza(“cheese”);
System.out.println(“Joel ordered a “ + pizza.getName() + “n”);
}
}

● The Factory Method Pattern deﬁnes an interface for
creating an object, but lets subclasses decide which
class to instantiate. Factory Method lets a class
defer instantiation to subclasses.
● It also helps to relate to parallel class hierarchies
(the Product and the Creator).

Dependency Inversion Principle
● Depend upon abstractions. Do not depend upon
concrete classes.
● A successor of this principle is Inversion of Control,
also known as Hollywood Principle (IoC in short).
● A successor of IoC is Dependency Injection
Principle.

Dependency Inversion Guidelines
● No variable should hold a reference to a concrete
class.
● No class should derive from a concrete class.
● No method should override an implemented method
of any of its base classes.

Resources
● Head First Design Pattern

Factory Method Pattern

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