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String concatenation results in CPU load

Andrei Antonescu
Ranch Hand

Joined: Jul 08, 2010
Posts: 75
Hello all,

I am using string concatenation in a while loop to create a really big string. Could this take the CPU load to 100% or should I look for somethig else for answers to the CPU load problem ?

Thanks,
Paul Clapham
Bartender

Joined: Oct 14, 2005
Posts: 18541
    
    8

Well, yes, it could. That's what the CPU is for, after all.

However there's a class called StringBuilder. You should be using that if you're building a string (hence the name) with a non-trivial amount of string concatenation.
Jeff Verdegan
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Joined: Jan 03, 2004
Posts: 6109
    
    6

Andrei Antonescu wrote:Hello all,

I am using string concatenation in a while loop to create a really big string. Could this take the CPU load to 100% or should I look for somethig else for answers to the CPU load problem ?

Thanks,


If by "concatenation" you mean either str += someOtherStr or the explicit use of the concatenate() method, then, yeah, that could be a problem for large strings in a tight loop.

However, rather than guessing at where the problem might be, you're better off using a profiler to measure it. JProbe, JProfiler, OptimizeIt, and AppPerfect all have either limited time or limited functionality demo versions, and the JDK comes with jvisualvm.
kurt marfori
Greenhorn

Joined: Jan 19, 2012
Posts: 12
You could also concatenate by simple using it like this System.out.print(""i+and so on);
fred rosenberger
lowercase baba
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Joined: Oct 02, 2003
Posts: 11256
    
  16

kurt marfori wrote:You could also concatenate by simple using it like this System.out.print(""i+and so on);

you could, but i believe that is also horribly inefficient.


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Jeff Verdegan
Bartender

Joined: Jan 03, 2004
Posts: 6109
    
    6

fred rosenberger wrote:
kurt marfori wrote:You could also concatenate by simple using it like this System.out.print(""i+and so on);

you could, but i believe that is also horribly inefficient.


I don't know. It's not even clear what he's saying.

If he's just talking about something like


Then it's about as efficient as you can get, in terms of CPU cycles. Of course, since the OP explicitly stated he's doing it in a loop, chances are good that this kind of approach is not possible.

And if that's not what he's talking about, then I have no clue what he means.
Deepak Bala
Bartender

Joined: Feb 24, 2006
Posts: 6661
    
    5

Could this take the CPU load to 100% or should I look for somethig else for answers to the CPU load problem ?


If it stays at 100% you are looking at an infinite loop instead of a string concat inefficiency. Yes concatenation is quite inefficient and StringBuilders help alleviate that. Depending on what you are trying to do, there could be other ways around concatenation. If you would like to explore other options do let us know what the concatenation attempts to achieve.


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Andrei Antonescu
Ranch Hand

Joined: Jul 08, 2010
Posts: 75
Thanks for posting. I am using StringBuilder.

I have a webapp that generates reports. It takes the report from the database, then uses string concatenation to build a json object that will later send to the client side (javascript).
Sometimes JSON objects are quite big.
A different approach would be to generate an XML directly at the database level and just send it to the client. The CPU doesn't go to 100%, it goes to something like 70% and there are a lot of requests to the webserver.
Can you please indicate me a better way of send data to the javascript side (javascript takes the data via ajax) ?.
 
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