About Design Patterns Singleton and Factory

E$w@r's link is a good one. In a nutshell Singletons are generally used prevent repeated load of a heavy resource in memory. Say class A has a big common dataset which is reusable. If many other objects access various instance of this object then it is a wastage of memory, because the same type of data repeated in memory. So singleton pattern prevents the multiple instance of it.

Singleton can be used to keep global data as well, if static members not satisfied.

Factory is by the name itself it explains creation of objects. Basically if you create an object by hardcode inside the class then your class need to be edited when a new type of objects need to create in a new condition. Instead of that you can separate the object creation to a factory and delegate the creation work to it. So any changes in the object creation will impact on the factory class coding, but no need to modify the classes which using the factory. Once the new condition is passed to the factory, the factory knows which object has to instantiate to do the job. The caller class doesn't need to worry about which object has to instantiate.

This is just a nutshell explanation


There are lot of good material available in internet. You can go through it.

The Question in not completely incorrect, but can be greatly improved. You should have re-formulated it:

"How to use Wikipedia, Google, CodeProject and StackOverflow.com?"

If you asked and got good Answers, the Questions like your original one would not be needed!

—SA

Here is a Lazy<Answer> :)
System.Lazy<T>[^]

Implements the singleton pattern in .Net ...

Best regards
Espen Harlinn