Hi Reddy ,
Singleton class comes into picture when there is common data which is frequently share/used by varoius module in ur application.
And creation of commonly shared data for every request is expensive for the application viz. Remote Lookup of Session Bean or loading and reading one property from property file.
There should only one static method which will return the instance of that singleton class.Because on-buddy can construct the object of ur Singleton class {coz constructor of ur singleton is private
}.
And as per me any static method is not suppose to manipulate Member Valiable realted data , coz if something goes wrong during the processing, then other request for that member will get wrong/unexpected result.
U always create static method for commond peice of code which take some input and process those input and return the result, e.g sorting.
Hope that this make more clear when to use static method and when to use Singleton class.
Sunil Dixit