Re: Serizlize You Cannot Use for Object Size

Sun, 26 Aug 2007 08:15:02 -0700
On Aug 25, 4:31 pm, Manivannan Palanichamy
<> wrote:

On Aug 25, 1:50 am, wrote:

One thread here said you can serialize object and count serialized
bytes to get the size of the object
This is incorrect. I serialize small class with one boolean and 2
chars and
got something crazy like 637 bytes for the size. I serialize to file
and you see the problem:

 =BC=CF=86 =E2=99=A3{sr =CF=

=84=C3=A5=E2=96=AC5=E2=98=BB xr
ptiond=E2=94=9C=CE=A3k=C3=AC9=E2=88=9A=E2=96=80=E2=98=BB xr =E2= =BD=E2=98=BB xr =E2=

java.lang.Exception=E2=95=A8 =B2=E2=96=BC>

There is many bytes serialized so you can't use this to count size of
object in bytes.

First of all, what is meant by Object's size? This is not C/ C++. In
C, C++ the object size is calculated by summing up the member
variables. But, in java, it depends on implementation. For example,
the java language specification just says that the boolean should take
either 'true' or 'false'. But, it doesnt force any constraints on the
implementation like, the boolean size should be 1 or 10 bytes. Some
implementation might represent a boolean variable in 1 single byte.
Some other implementation may represent the boolean varibale in 2
bytes or more. So, size is all about implementation specific.

One more thing, the 'Object Construction' is also implementation
specific. Assume, you declare 5 integers in a serialized class. So,
you think that the object instance size for the class will be (5 * 4)
20 bytes. But, that cant be the case always. Because, jvm might add
some internal fields to represent the 'serialized' feature. Or it
might do some trick over constructing the particular instance. So, no
guarantee that your measured 'size' will be accurate.

I would suggest not to talk about *size* in java. Talk about memory.

Manivannan Palanichamy (@) Oracle.com


So what is the way to compute the memory consumed by object? This is
hard to work with language that doesn't support this. Can anyone post
some code that work? Say you have this class what will is total memory
for each instance:

public class Goo implements Serializable {
  public int one;
  public boolean two;
  public boolean three;
  public double x;


This is something that programmer should be able to do on any
language. I cannot do it in java, but i am new. Can anyone do it?

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