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看一个具体的需求
看一个披萨的项目:要便于披萨种类的扩展,要便于维护
UML 类图
核心代码
public abstract class Pizza {
protected String name;
public void setName(String name) {
this.name = name;
}
public abstract void prepare();
public void bake() {
System.out.println(name + " baking...");
}
public void cut() {
System.out.println(name + " cutting...");
}
public void box() {
System.out.println(name + " boxing...");
}
}
//希腊风味披萨
public class GreekPizza extends Pizza {
@override
public void prepare() {
setName("GreekPizza");
System.out.println(name + " preparing...");
}
}
// 奶酪披萨
public class CheesePizza extends Pizza {
@Override
public void prepare() {
setName("CheesePizza");
System.out.println(name + " preparing...");
}
}
public class OrderPizza {
public OrderPizza() {
Pizza pizza = null;
String orderTyPE;
do {
orderType = getType();
if ("cheese".equals(orderType)) {
pizza = new CheesePizza();
} else if ("greek".equals(orderType)) {
pizza = new GreekPizza();
} else {
System.out.println("输入类型错误,程序退出");
break;
}
pizza.prepare();
pizza.bake();
pizza.cut();
pizza.box();
} while (true);
}
private String getType() {
System.out.println("请输入披萨类型:");
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
try {
return reader.readLine();
} catch (IOException e) {
e.printStackTrace();
return "";
}
}
}
传统方式优缺点
// 胡椒披萨
public class PepperPizza extends Pizza {
@Override
public void prepare() {
setName("PepperPizza");
System.out.println(name + " preparing...");
}
}
public class OrderPizza {
public OrderPizza() {
// ...
else if ("pepper".equals(orderType)) {
pizza = new PepperPizza();
}
// ...
}
// ...
}
改进的思路分析
UML 类图
核心代码
public class PizzaFactory {
public Pizza createPizza(String orderType) {
Pizza pizza = null;
swITch (orderType) {
case "cheese":
pizza = new CheesePizza();
break;
case "greek":
pizza = new GreekPizza();
break;
case "pepper":
pizza = new PepperPizza();
break;
default:
break;
}
return pizza;
}
}
public class OrderPizza {
private PizzaFactory pizzaFactory;
public OrderPizza(PizzaFactory pizzaFactory) {
this.pizzaFactory = pizzaFactory;
orderPizza();
}
public void orderPizza() {
Pizza pizza = null;
do {
pizza = pizzaFactory.createPizza(getType());
if (pizza == null) {
System.out.println("Failed to Order Pizza");
} else {
pizza.prepare();
pizza.bake();
pizza.cut();
pizza.box();
}
} while (true);
}
// ...
}
静态工厂模式也是简单工厂模式的一种,只是将工厂方法改为静态方法
UML 类图
核心代码
public class PizzaFactory {
public static Pizza createPizza(String orderType) {
// ...
}
}
public class OrderPizza {
public OrderPizza() {
Pizza pizza;
do {
pizza = PizzaFactory.createPizza(getType());
// ...
} while (true);
}
工厂方法模式设计方案:将披萨项目的实例化功能抽象成抽象方法,在不同的口味点餐子类中具体实现
工厂方法模式:定义了一个创建对象的抽象方法,由子类决定要实例化的类。工厂方法模式将对象的实例化推迟到子类
看一个新的需求
披萨项目新的需求:客户在点披萨时,可以点不同口味的披萨,比如北京的奶酪 Pizza、北京的胡椒 Pizza 或者是伦敦的奶酪 Pizza、伦敦的胡椒 Pizza
思路1:使用简单工厂模式,创建不同的简单工厂类,比如 BJPizzaFactory、LDPizzaFactory 等等。从当前这个案例来说,也是可以的,但是考虑到项目的规模,以及软件的可维护性、可扩展性并不是特别好
思路2:使用工厂方法模式
UML 类图
核心代码
public abstract class OrderPizza {
public void orderPizza() {
Pizza pizza = null;
do {
pizza = createPizza(getType());
if (pizza == null) {
System.out.println("Failed to Order Pizza");
} else {
pizza.prepare();
pizza.bake();
pizza.cut();
pizza.box();
}
} while (true);
}
public abstract Pizza createPizza(String orderType);
// ...
}
public class LDOrderPizza extends OrderPizza {
@Override
public Pizza createPizza(String orderType) {
Pizza pizza = null;
switch (orderType) {
case "cheese":
pizza = new LDCheesePizza();
break;
case "pepper":
pizza = new LDPepperPizza();
break;
default:
break;
}
return pizza;
}
}
public class BJOrderPizza extends OrderPizza {
@Override
public Pizza createPizza(String orderType) {
Pizza pizza = null;
switch (orderType) {
case "cheese":
pizza = new BJCheesePizza();
break;
case "pepper":
pizza = new BJPepperPizza();
break;
default:
break;
}
return pizza;
}
}
UML 类图
核心代码
public interface AbsPizzaFactory {
Pizza createPizza(String orderType);
}
public class BJPizzaFactory implements AbsPizzaFactory {
@Override
public Pizza createPizza(String orderType) {
Pizza pizza = null;
switch (orderType) {
case "cheese":
pizza = new BJCheesePizza();
break;
case "pepper":
pizza = new BJPepperPizza();
break;
default:
break;
}
return pizza;
}
}
public class LDPizzaFactory implements AbsPizzaFactory {
@Override
public Pizza createPizza(String orderType) {
Pizza pizza = null;
switch (orderType) {
case "cheese":
pizza = new LDCheesePizza();
break;
case "pepper":
pizza = new LDPepperPizza();
break;
default:
break;
}
return pizza;
}
}
JDK 中的 Calendar 类中,就使用了简单工厂模式
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