OOP Design (Head First Design Patterns) 学习笔记--05 The factory Pattern

When you see "new", think "concrete"!

1. Identify what varies

2. Encapsulate object creation

Factories handles the details of object creation.

3. Pizza franchise

4. Let the subclasses decide

A factory method handles object creation and encapsulates it in a subclass. This decouples the client code in the superclass from the object creation in the subclass.

abstract Product factoryMethod(String type)

5. Ordering a pizza

import java.util.ArrayList;

public abstract class Pizza {
String name;
String dough;
String sauce;
ArrayList<String> toppings = new ArrayList<String>();

void prepare() {
System.out.println("Preparing " + name);
System.out.println("Tossing dough...");
System.out.println("Adding sauce...");
System.out.println("Adding toppings: ");
for (int i = 0; i < toppings.size(); i++) {
System.out.println(" " + toppings.get(i));
}
}

void bake() {
System.out.println("Bake for 25 minutes at 350");
}
void cut() {
System.out.println("Cutting the pizza into diagonal slices");
}
void box() {
System.out.println("Place pizza in official PizzaStore box");
}

public String getName() {
return name;
}
}

public class ChicagoStyleCheesePizza extends Pizza {
public ChicagoStyleCheesePizza() {
name = "Chicago Style Deep Dish Cheese Pizza";
dough = "Extra Thick Crust Dough";
sauce = "Plum Tomato Sauce";

toppings.add("Shredded Mozzarella Cheese");
}

void cut() {
System.out.println("Cutting the pizza into square slices");
}
}

public class NYStyleCheesePizza extends Pizza {
public NYStyleCheesePizza() {
name = "NY Style Sauce and Cheese Pizza";
dough = "Thin Crust Dough";
sauce = "Marinara Sauce";

toppings.add("Grated Reggiano Cheese");
}
}

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 ChicagoPizzaStore extends PizzaStore {
protected Pizza createPizza(String item) {
if (item.equals("Cheese")) {
return new ChicagoStyleCheesePizza();
} else return null;
}
}

public class NYPizzaStore extends PizzaStore {
protected Pizza createPizza(String item) {
if (item.equals("Cheese")) {
return new NYStyleCheesePizza();
} else return null;
}
}

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 orderded a " + pizza.getName() + "\n");
}
}