简单工厂设计模式

目录

1、代码

2、概述与总结

3、代码改进

4、其他源码实际应用

---

1、代码

直接放一个简单工厂的代码：

package 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;
    }

}

调用类的代码：

package 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.produce();

    }

}

2、概述与总结

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

如果产品类别过多，则工厂类的逻辑会比较复杂

无法形成基于继承的等级结构

 

3、代码改进

我们可以将VideoFactory类中的if..else判断，改为反射生成对象的方式，直接需要什么对象，就传参什么类。

代码如下：

详见https://github.com/phs999/DesignPatterns/tree/24def2f8c68db4cd9671760623cda155c4f2b824/design_pattern/src/creational/simplefactory

package 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;
    }

}

package 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.produce();

    }

}

4、其他源码实际应用

（1）java.util.Calendar通过参数判断，进而生成不同的具体对象。

private static Calendar createCalendar(TimeZone zone,
                                           Locale aLocale)
    {
        CalendarProvider provider =
            LocaleProviderAdapter.getAdapter(CalendarProvider.class, aLocale)
                                 .getCalendarProvider();
        if (provider != null) {
            try {
                return provider.getInstance(zone, aLocale);
            } catch (IllegalArgumentException iae) {
                // fall back to the default instantiation
            }
        }

        Calendar cal = null;

        if (aLocale.hasExtensions()) {
            String caltype = aLocale.getUnicodeLocaleType("ca");
            if (caltype != null) {
                switch (caltype) {
                case "buddhist":
                cal = new BuddhistCalendar(zone, aLocale);
                    break;
                case "japanese":
                    cal = new JapaneseImperialCalendar(zone, aLocale);
                    break;
                case "gregory":
                    cal = new GregorianCalendar(zone, aLocale);
                    break;
                }
            }
        }
        if (cal == null) {
            // If no known calendar type is explicitly specified,
            // perform the traditional way to create a Calendar:
            // create a BuddhistCalendar for th_TH locale,
            // a JapaneseImperialCalendar for ja_JP_JP locale, or
            // a GregorianCalendar for any other locales.
            // NOTE: The language, country and variant strings are interned.
            if (aLocale.getLanguage() == "th" && aLocale.getCountry() == "TH") {
                cal = new BuddhistCalendar(zone, aLocale);
            } else if (aLocale.getVariant() == "JP" && aLocale.getLanguage() == "ja"
                       && aLocale.getCountry() == "JP") {
                cal = new JapaneseImperialCalendar(zone, aLocale);
            } else {
                cal = new GregorianCalendar(zone, aLocale);
            }
        }
        return cal;
    }