简单工厂模式（Simple Factory）

定义与类型

定义：由一个工厂对象决定创建出哪一种产品类的实例

类型：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（应用层）只知道传入工厂类的参数，对于如何创建对象（逻辑）不关心

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，而无须知道其创建细节

缺点

工厂类的职责相对过重，增加新的产品时，需要修改工厂类的判断逻辑，违背开闭原则

简单工厂代码示例

Video.java

package com.czh.creational.simplefactory;

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

JavaVideo.java

package com.czh.creational.simplefactory;

public class JavaVideo extends Video {
    @Override
    public void play() {
        System.out.println("播放Java视频");
    }
}

PythonVideo.java

package com.czh.creational.simplefactory;

public class PythonVideo extends Video {
    @Override
    public void play() {
        System.out.println("播放Python视频");
    }
}

VideoFactory.java

package com.czh.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;
    }
}

Test.java

package com.czh.creational.simplefactory;

public class Test {
    public static void main(String[] args) {
        VideoFactory videoFactory = new VideoFactory();
        Video video = videoFactory.getVideo("java");
        if (video == null) {
            return;
        }
        video.play();
    }
}

使用反射演进简单工厂

Video.java

package com.czh.creational.simplefactory;

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

JavaVideo.java

package com.czh.creational.simplefactory;

public class JavaVideo extends Video {
    @Override
    public void play() {
        System.out.println("播放Java视频");
    }
}

PythonVideo.java

package com.czh.creational.simplefactory;

public class PythonVideo extends Video {
    @Override
    public void play() {
        System.out.println("播放Python视频");
    }
}

VideoFactory.java

package com.czh.creational.simplefactory;

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

Test.java

package com.czh.creational.simplefactory;

public class Test {
    public static void main(String[] args) {
        VideoFactory videoFactory = new VideoFactory();
        Video video = videoFactory.getVideo(JavaVideo.class);
        if (video == null) {
            return;
        }
        video.play();
    }
}