10/06: Factory Patterns of DP

• Simple factory pattern
• the instantiation logic will be written in factory method
• ….

            if (!String.IsNullOrEmpty(fruitType))
            {
                switch (fruitType)
                {
                    case "Apple":
                        return new Apple();
                    case "Orange":
                        return new Orange();
                    case "Pear":
                        return new Pear();
                    case "Banana":
                        return new Banana();
                }
            }

• Against Open-Close rule when adding new instance which need to modify above code

 

 

• Factory Pattern
• the instantiation logic will be written in client application
• ….

   //首先要实例化一个苹果工厂
            factory = new AppleFactory();
     //然后通过工厂来获得苹果类对象
            fruit = factory.GetFruit();
   //访问苹果类对象
fruit.Display();

  //首先要实例化一个梨子工厂
            factory = new PearFactory();
//然后通过工厂来获得梨子类对象
            fruit = factory.GetFruit();
//访问梨子类对象
            fruit.Display();

工厂方法将这些本来应该存在的判断逻辑移到了客户端代码中，

（通过客户的需求来选择生成那一种水果实例，比如我的演示中生成的就是苹果和梨子这两种实例

• Not against open-close rule when adding new instance.
• Abstract Factory Pattern.
• Abstract factory pattern is very similar as factory pattern.
• Difference :
• Factory pattern is better used for adding a new object under same family( like add a new peachfactory item to fruitfacotry family)
• Abstract pattern is better used for adding a new brand new family which share similarly with existing family(like database operation component for Oracle , Sqlserver , DB2, SAP, etc).
• Abstract factory return factory object while factory return its subclass object.(so abstract factory is one level higher than factory )