简单工厂

定义

由一个工厂对象决定创建出哪一种产品类的实例。
属于创建型，但不属于GOF23种设计模式。

适用场景

工厂类负责创建的对象比较少
客户端只知道传入工厂类的参数，不关心创建对象的具体逻辑。

优点

只需要传入一个正确的参数，就可以获取你所需要的对象，而无需知道其创建细节。

缺点

工厂类的职责相对过重，增加新的产品需要修改工厂类的判断逻辑，违背开闭原则。

Coding

错误代码

package design.creational.simplefactory;

public abstract class Video {
    public abstract void produce();
}

package design.creational.simplefactory;

public class JavaVideo extends Video {
    @Override
    public void produce() {
        System.out.println("这是Java视频课程");
    }
}

package design.creational.simplefactory;

public class PythonVideo extends Video {
    @Override
    public void produce() {
        System.out.println("这是Python视频课程");
    }
}

package design.creational.simplefactory;

public class Test {
    public static void main(String[] args) {
        // 此时Test类依赖于JavaVideo类或PythonVideo类
        Video video = new JavaVideo();
        video.produce();
    }
}

正确代码(但违背开闭原则)

package design.creational.simplefactory;

public class VideoFactory {
    public Video getVideo(String type) {
        if ("Java".equalsIgnoreCase(type)) {
            return new JavaVideo();
        } else if ("Python".equalsIgnoreCase(type)) {
            return new PythonVideo();
        }
        return null;
    }
}

package design.creational.simplefactory;


public class JavaVideo extends Video {
    @Override
    public void produce() {
        System.out.println("这是Java视频课程");
    }
}

package design.creational.simplefactory;

public class PythonVideo extends Video {
    @Override
    public void produce() {
        System.out.println("这是Python视频课程");
    }
}

package design.creational.simplefactory;

public class Test {
    public static void main(String[] args) {
        VideoFactory videoFactory = new VideoFactory();
        Video video = videoFactory.getVideo("Java");
        video.produce();
    }
}

正确代码

package design.creational.simplefactory;

public class VideoFactory {
//    public Video getVideo(String type) {
//        if ("Java".equalsIgnoreCase(type)) {
//            return new JavaVideo();
//        } else if ("Python".equalsIgnoreCase(type)) {
//            return new PythonVideo();
//        }
//        return null;
//    }

    public Video getVideo(Class c) {
        Video video = null;
        try {
            video = (Video) Class.forName(c.getName()).newInstance();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return video;
    }
}

package design.creational.simplefactory;

public class Test {
    public static void main(String[] args) {
//        VideoFactory videoFactory = new VideoFactory();
//        Video video = videoFactory.getVideo("Java");
//        video.produce();
        VideoFactory videoFactory = new VideoFactory();
        Video video = videoFactory.getVideo(JavaVideo.class);
        video.produce();
    }
}