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How to find the Size Of an Object ?

Venkat Ramayanam
Greenhorn

Joined: Apr 25, 2006
Posts: 5
Hi,
Pls could some one tell me how to find the size of an object??
I know that there is no sizeof operator in java,but is there any direct way of finding it out?
Does the following code accomplish the task?

java.lang.instrument.Instrumentation.getObjectSize(Object objectToSize)
Rajah Nagur
Ranch Hand

Joined: Nov 06, 2002
Posts: 239
Check this out


You can't wake a person who is <b><i>pretending</i></b> to be asleep.<br />Like what <b>"it"</b> does not like - <i> Gurdjieff </i>
Peter Chase
Ranch Hand

Joined: Oct 30, 2001
Posts: 1970
Why do you want to know the size of an object in memory? Java insulates the programmer from that sort of thing and 99% of the time, that's exactly what you want.


Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.
Pradeep Kadambar
Ranch Hand

Joined: Oct 18, 2004
Posts: 148
As Peter said

Why do you want to know the size of an object in memory?


There is no necessity for this. Many of us migrating form C/C++ to Java have the tendency to think in the same grounds as the former.

Here the articles clearly addresses the same issues.
Sizeof for Java

Data Size

I hope these articles will clear off your doubts.
Stan James
(instanceof Sidekick)
Ranch Hand

Joined: Jan 29, 2003
Posts: 8791
There are plenty of reasons to want to know this. In making a design choice I might prefer the one that takes less memory. I might have a good idea of how many objects I'll have and want to predict how much memory I'll need to buy. I might have an out of memory issue and want to know which object is causing it.

Unfortunately all those reasons don't help with the answer: we don't know.

We have used some tools from IBM that read verbose logs and give a report of object allocations - class name & size and so on. This helped us learn that a logger (for which we have no source) was making 5 or 6 copies of a many-megabyte log message (which we eliminated!), causing allocation errors in several unrelated areas of the app.


A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi
Peter Chase
Ranch Hand

Joined: Oct 30, 2001
Posts: 1970
If you need the size of an object for debugging memory problems, hprof will tell you the size, won't it? I thought the question was about getting the size programmatically within an ordinary application, which is something you can't do.

I've just been doing some hprof. Here's a little extract from my hprof output. You can clearly see the sizes (sz) of the objects and arrays.

 
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