设计模式之工厂模式 - JAVA

本章分三部分：简单工厂，工厂方法模式，抽象工厂模式。

一、简单工厂：简单工厂其实不是一个设计模式，只是一种编程习惯。示例如下：

PizzaStore.java

package headfirst.factory.pizzas;

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;
	}
}

SimplePizzaFactory.java

package headfirst.factory.pizzas;

public class SimplePizzaFactory {

	public Pizza createPizza(String type) {
		Pizza pizza = null;

		if (type.equals("cheese")) {
			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;
	}
}

Pizza类是一个抽象基类，其他具体Pizza类均继承自他，在此不再列出代码。

测试：

package headfirst.factory.pizzas;

public class PizzaTestDrive {
 
	public static void main(String[] args) {
		SimplePizzaFactory factory = new SimplePizzaFactory();
		PizzaStore store = new PizzaStore(factory);

		Pizza pizza = store.orderPizza("cheese");
		System.out.println("We ordered a " + pizza.getName() + "\n");
 
		pizza = store.orderPizza("veggie");
		System.out.println("We ordered a " + pizza.getName() + "\n");
	}
}

二、工厂方法模式

此模式定义了一个创建对象的接口，但由子类决定要实例化的类是哪一个。工厂方法让类把实例化推迟到子类。

简单描述：由子类决定要创建的具体类是哪一个

示例：

PizzaStore.java(createPizza()声明成抽象方法，由子类实现，从而由子类决定要创建的具体pizza是什么)

package headfirst.factory.pizzafm;

public abstract class PizzaStore {
 
	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;
	}
}

NYPizzaStore.java(具体的pizza店类)

package headfirst.factory.pizzafm;

public class NYPizzaStore extends PizzaStore {

	Pizza createPizza(String item) {
		if (item.equals("cheese")) {
			return new NYStyleCheesePizza();
		} else if (item.equals("veggie")) {
			return new NYStyleVeggiePizza();
		} else if (item.equals("clam")) {
			return new NYStyleClamPizza();
		} else if (item.equals("pepperoni")) {
			return new NYStylePepperoniPizza();
		} else return null;
	}
}

其他代码就不贴了，这两个类已经足于展示工厂方法模式的原理。

测试：

package headfirst.factory.pizzafm;

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");

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

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

设计模式之工厂模式(一)