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Why cant we instance variables in servlets

 
raj talatam
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Many people says that we should not instance variable in Servlets , it is very Dangerious

Why.................
 
Kunal Lakhani
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I am not sure about the reason, but i think that servlet are initialized only once. And after that it processes only request , so only service method is invoked.

Am i correct? if not, give the reason behind this?

Thanks
 
Seetharaman Venkatasamy
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there is only one instance for a servlet and many user/many threads/many request may access the instance concurrently. i.e, many threads run on the single instance and it is obvious instance variables are shared by concurrent threads, hence unexpected result which use the instance variable
 
Seetharaman Venkatasamy
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also Please search here. similar question discussed many time.
 
Tim Moores
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Note that shared data (like an instance variable in multi-threaded code like a servlet) is only a problem if it's mutable. If the data never changes, then there's no problem.
 
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