设计模式之抽象工厂模式

定义

抽象工厂模式提供一个创建一系列相关或相互依赖对象的接口，而无需指定它们具体的类

角色

• 抽象产品类A
• 抽象产品类B
• 抽象工厂类
• 具体工厂类C（生成A）
• 具体工厂类D（生产B）

UML类图

抽象工厂模式UML类图

代码

• IBenz.java

public interface IBenz {
    void run();
}

• IBWM.java

public interface IBWM {
    void run();
}

• HomeUseBenz.java

public class HomeUseBenz implements IBenz {
    @Override
    public void run() {
        System.out.println("first.HomeUseBenz run");
    }
}

• HomeUseBWM.java

public class HomeUseBWM implements IBWM {
    @Override
    public void run() {
        System.out.println("first.HomeUseBWM run");
    }
}

• BusinessUseBenz.java

public class BusinessUseBenz implements IBenz {
    @Override
    public void run() {
        System.out.println("first.BusinessUseBenz run");
    }
}

• BusinessUseBWM.java

public class BusinessUseBWM implements IBWM {
    @Override
    public void run() {
        System.out.println("first.BusinessUseBWM run");
    }
}

• AbstarctFactory.java

public abstract class AbstarctFactory {
    public abstract IBWM createBWM();
    public abstract IBenz createBenz();
}

• HomeUseFactory.java

public class HomeUseFactory extends AbstarctFactory {
    @Override
    public IBWM createBWM() {
        return new HomeUseBWM();
    }
    @Override
    public IBenz createBenz() {
        return new HomeUseBenz();
    }
}

• BusinessFactory.java

public class BusinessFactory extends AbstarctFactory {
    @Override
    public IBWM createBWM() {
        return new BusinessUseBWM();
    }              
    @Override
    public IBenz createBenz() {
        return new BusinessUseBenz();
    }
}

抽象工厂模式的优点

• 1 易于交换产品系列，由于具体工厂类，在一个应用中只需要在初始化的时候出现一次，这就使得改变一个应用的具体工厂变得非常容易，它只需要改变具体工厂即可使用不同的产品配置
• 2 它让具体的创建实例的过程与客户端分离，客户端是通过它们的抽象接口操作实例，产品的具体类名也被具体工厂的实现分离，不会出现在客户代码中

抽象工厂模式的缺点

如果想要增加一个不同的车型，则需要增加三个类以及修改三个工厂，比较繁琐！

使用简单工厂改进抽象工厂

UML类图

简单工厂改进抽象工厂UML.png

代码

• AllFactory.java

public class AllFactory {
    private static final String type = "home";
    //private static final String type = "business";
    public static IBenz createBenz(){
        IBenz benz = null;
        switch (type){
            case "home":
                benz = new HomeUseBenz();
                break;
            case "business":
                benz = new BusinessUseBenz();
                break;
        }
        return benz;
    }
    public static IBWM createBWM(){
        IBWM bwm = null;
        switch (type){
            case "home":
                bwm = new HomeUseBWM();
                break;
            case "business":
                bwm = new BusinessUseBWM();
                break;
        }
        return bwm;
    }
}

使用反射改进抽象工厂方法

public class AllFactory {
    private final static String type="homeUse";
    //private final static String type="businessUse";

    public static IBenz createBenz() throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        String className = type.substring(0, 1).toUpperCase() + type.substring(1) + "Benz";
        //获取包路径
        String packageName = new Object() {
            public String getPackageName() {
                return this.getClass().getPackage().getName();
            }
        }.getPackageName();
        Class<? extends IBenz> clazz = (Class<? extends IBenz>) Class.forName(packageName+"."+className);
        return clazz.newInstance();
    }
    public static IBWM createBWM() throws IllegalAccessException, InstantiationException, ClassNotFoundException {
        String className = type.substring(0, 1).toUpperCase() + type.substring(1) + "BWM";
        //获取包路径
        String packageName = new Object() {
            public String getPackageName() {
                return this.getClass().getPackage().getName();
            }
        }.getPackageName();
        Class<? extends IBWM> clazz = (Class<? extends IBWM>) Class.forName(packageName +"."+className);
        return clazz.newInstance();
    }
}