如果在OOP中使用过多的单例和静态方法，会有什么风险？

Question

I've written OOP programs for almost two years. But recently I find that I always prefer using too many singletons and static methods in my OOP projects.

For example, in order to decouple codes, I'd like to use MVC or something like 3-tier architecture. I usually use Models to temporarily store information, such as user's login token or his or her profile. I find that in most case, I just need one instance of a model class. So almost all of my Models are written in Singleton style.

And in the Business Logic Layer or Controller, I hardly can find a situation to use multi instances to call a same method, except for multithreading reasons. That cause most of my BLL are constructed by static methods or class!

I know this question is abstract and not really a good question for StackOverflow. But I myself feel really confusing about this. I think this kind of coding style does not really a OOP style, but I cannot find a better way to solve these logic problems above.

Answer 1

There is only one good reason to use a Singleton. When It is necessary that there is only one instance of the class. I mean, It cannot be more of one instance.

Examples:

• Your logger. You open a file to save the data. If other instance is called. You would have several log files...

• A class to send things to a printing machine. You will need to open the driver of the printer. If you create two of this you get errors trying to open twice the driver.

If you only create one instance of your classes, it means that you do not need more TODAY. Do not auto-constraint yourself.

It is a bad solution to use a pattern that was created for other purpose.