factory

factory 模式 从若干个可能类创建对象
        
       
public interface IHelloPrinter
{
    void PrintHello();
}

public class EnglishHelloPrinter:IHelloPrinter
{
        void PrintHello(){ System.Console.write("");
            }

}

public class GermanHelloPrinter:IHelloPrinter
{
        void PrintHello(){ System.Console.write("");
            }

}

public class HelloFactory
{
    public IHelloPrinter CreateHelloPrinter(string language)
        {
            switch(language)
            {
                case "de":
                        return new GermanHelloPrinter();
                case "en":
                        return new EnglishHelloPrinter();
             }
        }
}