设计模式：工厂

模拟不同披萨店制作不同口味的披萨的情景。

首先定义main方法，它需要各种各样的披萨。

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 + "\n");

pizza = chicagoStore.orderPizza("cheese");
System.out.println("Joel ordered a " + pizza + "\n");

pizza = nyStore.orderPizza("clam");
System.out.println("Ethan ordered a " + pizza + "\n");

pizza = chicagoStore.orderPizza("clam");
System.out.println("Joel ordered a " + pizza + "\n");

pizza = nyStore.orderPizza("pepperoni");
System.out.println("Ethan ordered a " + pizza + "\n");

pizza = chicagoStore.orderPizza("pepperoni");
System.out.println("Joel ordered a " + pizza + "\n");

pizza = nyStore.orderPizza("veggie");
System.out.println("Ethan ordered a " + pizza + "\n");

pizza = chicagoStore.orderPizza("veggie");
System.out.println("Joel ordered a " + pizza + "\n");
}
}

由上可知，它找到两个披萨店，然后定分别在两家店定了四分不同披萨。接下来我们看看这两家店是怎么做的。

public abstract class PizzaStore {

protected abstract Pizza createPizza(String item);

public Pizza orderPizza(String type) {
Pizza pizza = createPizza(type);
System.out.println("--- Making a " + pizza.getName() + " ---");
pizza.prepare();
pizza.bake();
pizza.cut();
pizza.box();
return pizza;
}
}

第一家店

public class NYPizzaStore extends PizzaStore {

protected Pizza createPizza(String item) {
Pizza pizza = null;
PizzaIngredientFactory ingredientFactory =
new NYPizzaIngredientFactory();

if (item.equals("cheese")) {

pizza = new CheesePizza(ingredientFactory);
pizza.setName("New York Style Cheese Pizza");

} else if (item.equals("veggie")) {

pizza = new VeggiePizza(ingredientFactory);
pizza.setName("New York Style Veggie Pizza");

} else if (item.equals("clam")) {

pizza = new ClamPizza(ingredientFactory);
pizza.setName("New York Style Clam Pizza");

} else if (item.equals("pepperoni")) {

pizza = new PepperoniPizza(ingredientFactory);
pizza.setName("New York Style Pepperoni Pizza");

}
return pizza;
}
}

第二家店

public class ChicagoPizzaStore extends PizzaStore {

protected Pizza createPizza(String item) {
Pizza pizza = null;
PizzaIngredientFactory ingredientFactory =
new ChicagoPizzaIngredientFactory();

if (item.equals("cheese")) {

pizza = new CheesePizza(ingredientFactory);
pizza.setName("Chicago Style Cheese Pizza");

} else if (item.equals("veggie")) {

pizza = new VeggiePizza(ingredientFactory);
pizza.setName("Chicago Style Veggie Pizza");

} else if (item.equals("clam")) {

pizza = new ClamPizza(ingredientFactory);
pizza.setName("Chicago Style Clam Pizza");

} else if (item.equals("pepperoni")) {

pizza = new PepperoniPizza(ingredientFactory);
pizza.setName("Chicago Style Pepperoni Pizza");

}
return pizza;
}
}

注意这两家店的原料原料供应商来自不同的工厂。

先看作为供应商需要提供什么东西。

public interface PizzaIngredientFactory {

public Dough createDough();
public Sauce createSauce();
public Cheese createCheese();
public Veggies[] createVeggies();
public Pepperoni createPepperoni();
public Clams createClam();

}

两家供应商的分别实现。

public class ChicagoPizzaIngredientFactory
implements PizzaIngredientFactory
{

public Dough createDough() {
return new ThickCrustDough();
}

public Sauce createSauce() {
return new PlumTomatoSauce();
}

public Cheese createCheese() {
return new MozzarellaCheese();
}

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public Veggies[] createVeggies() {
Veggies veggies[] = { new BlackOlives(),
new Spinach(),
new Eggplant() };
return veggies;
}

public Pepperoni createPepperoni() {
return new SlicedPepperoni();
}

public Clams createClam() {
return new FrozenClams();
}
}

public class NYPizzaIngredientFactory implements PizzaIngredientFactory {

public Dough createDough() {
return new ThinCrustDough();
}

public Sauce createSauce() {
return new MarinaraSauce();
}

public Cheese createCheese() {
return new ReggianoCheese();
}

public Veggies[] createVeggies() {
Veggies veggies[] = { new Garlic(), new Onion(), new Mushroom(), new RedPepper() };
return veggies;
}

public Pepperoni createPepperoni() {
return new SlicedPepperoni();
}

public Clams createClam() {
return new FreshClams();
}
}

以上实现了接口方法，说明了他们能提供的不同口味的东西。

原料都备齐了。现在开始做披萨了。

public abstract class Pizza {
String name;

Dough dough;
Sauce sauce;
Veggies veggies[];
Cheese cheese;
Pepperoni pepperoni;
Clams clam;

abstract void prepare();

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");
}

void setName(String name) {
this.name = name;
}

String getName() {
return name;
}

public String toString() {
StringBuffer result = new StringBuffer();
result.append("---- " + name + " ----\n");
if (dough != null) {
result.append(dough);
result.append("\n");
}
if (sauce != null) {
result.append(sauce);
result.append("\n");
}
if (cheese != null) {
result.append(cheese);
result.append("\n");
}
if (veggies != null) {
for (int i = 0; i < veggies.length; i++) {
result.append(veggies[i]);
if (i < veggies.length-1) {
result.append(", ");
}
}
result.append("\n");
}
if (clam != null) {
result.append(clam);
result.append("\n");
}
if (pepperoni != null) {
result.append(pepperoni);
result.append("\n");
}
return result.toString();
}
}

除了准备材料，其他步骤都是相同的。所以，要做不同类的披萨，其区别只在于用的材料不相同。

它的实现类只要复写其准备材料的方法就行。

public class CheesePizza extends Pizza {
PizzaIngredientFactory ingredientFactory;

public CheesePizza(PizzaIngredientFactory ingredientFactory) {
this.ingredientFactory = ingredientFactory;
}

void prepare() {
System.out.println("Preparing " + name);
dough = ingredientFactory.createDough();
sauce = ingredientFactory.createSauce();
cheese = ingredientFactory.createCheese();
}
}

由上面例子可知，工厂模式模拟不同供应商。提供多种多样的选择。