Re: Static Method performance

[Curt Smith <chsmith@speakeasy.net>]

> Say there are 500 objects which have to use a certain method X ( exampled
> below).
> If i make X as static then 499 objects would have to queue up for access to
> the method, 


Note that static does not mean synchronized.

Your example would allow all threads to access your data[] array
concurrently.  This is ok, even safe if your data does not change
at run time.  Even if it does change, there's several operations
that the VM assures to be atomic.  Not enough space here for
that.

If data[] is big or expensive to create, this is a perfect candidate
for a static method and members.   You can still have a synchronized
mutator to change out the whole data array or just an index, leveraging
atomicity of a variable equate operation.  But your business data
may have more state that all needs to be consistant for this simplistic
discussion about what's atomic and safe in a concurrent environment.

re: the performance advantage, my guess is that the 15% perf advantage
is entirely due to new object () and garbage collection for the
non-static test case.  If the same object's method was being called
and vs creating a new object each time,
I'd be surprised that some vendor's JIT wouldn't be able to remove any perf.
difference.   TBD

curt


while if i make X an instance variable then each of 500 objects
> would have their own copy of the X's object and hence a copy of X.
> 
> public class Y
> {
> String[] data = new String[100];
> 
> public String[] X(int i)
> {
>       return (data[i],data[i+1].....data[i+10]);
> }
> 
> }
> 
> I understand that if i make X as static then data would also be a static
> variable.
> 
> Hope i have been able to express my question correctly.
> 
> Thanks
> Mayank
> 
> ----- Original Message -----
> From: "Brian Lee" <brian_a_lee@hotmail.com>
> To: <aggarwalmayank@hotmail.com>; <ajug-members@www.ajug.org>
> Sent: Wednesday, February 27, 2002 1:34 PM
> Subject: Re: Static Method performance
> 
> 
> 
>>I've seen about a 15% increase in performance between the same method
>>
> static and non-static. The test is pretty basic (do this 1000000 times and
> time it) so I don't have real-world data.
> 
>>The only downside I've experienced with static methods is that if your
>>
> class is implementing an interface, the interface defined methods can't be
> static.
> 
>>Other than this, I make as many methods as possible static (and final) for
>>
> performance reasons. Since most of the code I write doesn't go into a
> published API, I declare final and then change it if extending becomes
> necessary.
> 
>>BAL
>>
>>
>>>From: "Mayank Aggarwal" <aggarwalmayank@hotmail.com>
>>>To: <ajug-members@www.ajug.org>
>>>Subject: Static Method performance
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>>>
>>>How does static method affect performance in Java?
>>>
>>>I understand that all the method variables are created on Stack and hence
>>>
> each calling party gets its own stack of variables, hence there should not
> be problems of concurrency as long as only method local variables are
> manipulated.
> 
>>>What other reasons are there for not using a static methods ?
>>>
>>>
>>>Thanks
>>>Mayank
>>>
>>
>>
>>
> 


-- 

Curt Smith
chsmith@speakeasy.net
(w) 404-463-0973
(h) 404-294-6686