简单工厂

github https://github.com/spring2go/core-spring-patterns

定义

具有产品制造方法的工厂类，该方法能够根据不同的输入制造输
出不同的产品

public class NoFactoryMain {

	public static void main(String[] args) {
		TableFan fan = new TableFan();
		fan.switchOn();
	}

}

class TableFan {
	public void switchOn() {
		System.out.println("The TableFan is switched on ...");
	}
}

问题

• 客户知道类的构造细节，耦合变更问题
  • 类名变更
  • 参数变更
• 难于优化对象创建流程
  • 缓存

简单工厂关系图

定义 风扇 产品接口

public interface IFan {

    public void swithOn();

    public void switchOff();

}

吊扇的实现

public class CeilingFan implements IFan {

	@Override
	public void swithOn() {
		System.out.println("The CeilingFan is swithed on ...");
	}

	@Override
	public void switchOff() {
		System.out.println("The CeilingFan is swithed off ...");
	}
}

排风扇的实现

public class ExhaustFan implements IFan {

    @Override
    public void swithOn() {
        System.out.println("The ExhaustFan is swithed on ...");
    }

    @Override
    public void switchOff() {
        System.out.println("The ExhaustFan is swithed off ...");
    }
}

定义风扇的类型

public enum FanType {
	TableFan, //台扇
	CeilingFan, //吊扇
	ExhaustFan // 排风扇
}

定义 生产风扇的工厂的接口

public interface IFanFactory {
	IFan createFan(FanType type);
}

生产风扇工厂的具体实现

public class FanFactory implements IFanFactory {

	@Override
	public IFan createFan(FanType type) {
		switch (type) {
		case TableFan:
			return new TableFan();
		case CeilingFan:
			return new CeilingFan();
		case ExhaustFan:
			return new ExhaustFan();
		default:
			return new TableFan();
		}
	}

}

客户端调用

public class SimpleFactoryMain {

	public static void main(String[] args) {
		IFanFactory simpleFactory = new FanFactory();
		// 使用简单工厂创建一个电扇
		IFan fan = simpleFactory.createFan(FanType.TableFan);
		fan.swithOn();
		fan.switchOff();
	}

}

好处

• 产品制造流程集中到工厂，客户只和工厂打交道
  • 易于变更
  • 易于优化

缺点

1. 如果扩展需要修改原代码，易出bug