Caching Long Objects

Hi,
I would like to know why is Long objects are not cached internally and pooled in Java. Since Long objects are immutable there shouldn't be any problem in doing this right? Let me know am I missing anything here...Currently for one of my applications Iam planning to do this caching of Long objects myself. But the code for that looked pretty ugly as I need to put the newly constructed Long object into a HashMap and get the reference to the previously cached Long object. I believe providing this implementation will reduce my application memory requriements drastically as I need to cache huge volumes of data (around 1 GB of data need to be cached). Will there be any problems in providing an implementation like this ... Are there any better alternatives ?

Objects in general take somewhere in the region of 24-32 bytes to represent (excluding any member
variables) therefore Long will require somewhere in the region of 32 to 40 bytes to represent. The
hashMap you use to cache your Longs creates additional overhead (we'll ignore this for now as it can be
amortised over the individual unique Longs that you cache.
a long takes 8 bytes to store.
a reference takes 4 bytes (on a 32 bit machine 8 on a 64 bit JVM)
Therefore on 64 bit machines there is no advantage. Caching will always take more memory then using
native longs.
on a 32 bit VM the advantage of using cached Longs when compared to native longs occurs when you
have an average of at least 8 references to each unique Long. (for a large number of unique Longs)
However there are, I believe, plans to do this in 1.5. However they are not doing it to save memory. They
are doing it to improve the performance of autoboxing. Also the cache will not be dynamic it will be of
fixed size and created when the VM starts up. Basically values in the range -128 to 127 (or something
similar) will be cached for byte, short, int , long.
matfud

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Hi,
I want to know what is the way to change the value of a Long object (if any).
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That's not possible. Long is immutable (as are String, and all other primitive wrapper classes). This is done because immutable objects have huge advantages in many cases (like when acting as the key to a hashmap).

How to cache the objects MANUALLY?

hello
some o-r mapping tools can cache the objects that have been queried,then next time these objects are required,it don't need to access the database again,it can also monitor the database updating.
i wonder how i can implement such "cache" function MANUALLY? because i DON'T want to use ANY o-r mapping tools. i only use the jdbc to query database,then generate the object.
who can give me some clue?? or articles? or sample codes??
thank you!!!!!

no you don't understand me,what i want to know is the
mechanism of the cache,and how to implement it myself
without using the o-r mapping tools.
the dao pattern can encapsulate the database
access,but it can NOT cache the object .First you need to define how the caching occurs.
- Can the data in the database change without going through your code?
- Are there multiple copies of your app running at the same time. If yes then what happens if one is updated?
- How many of these can there be and what impact will this have on memory?
- etc.
You also need to identify the 'identity' of an object.
A simple strategy....
- Some layer requests an object using the 'identity'.
- The database layer code looks in a hash for the 'identity'. If it finds it it returns it.
- If it doesn't find it it uses a DAO to load it, then puts it in the hash, then returns it.

Efficiency of Long objects over Integer objects? any ?

I have a Long object which actually only stores "integer" values and we had coded it that way long before we realised it. Now I am told we need to change the LONG object to INTEGER object to improve Java efficiency. I disagree with that. Note that we are not doing any ARITHMETIC operations on the Long object at all. I understand that it would be efficient to use Integer object if theres a lot of arithmetic operations being done on it. But since we are not how is converting of Long objects to Integer going to improve my efficiency? and moreover since only integer values are stored in the Long object I dont see any memory allocation lose too....am i right in my posture?
Thanks

Thanks for quick reply ! are you saying Long and
Integer occupy same amount of memory space if the Long
object contains integer value ?No.
You said:
moreover since only integer values are stored in the Long
object I dont see any memory allocation lose too....am i right in my posture?I took that to mean that you thought that since the Longs contain a smaller (int-sized) values, that they're taking up the same space as Integers, and therefore you won't save any memory by switching to Integers.
That's not in fact the case. A Long takes up the same amount of space regardless of whether it's holding 0 or 1 or Integer.MAX_VALUE or Long.MAX_VALUE, and that space is probably slightly bigger (2 bytes bigger, I'd guess) than what Integer uses.
So technically, you will save some space (probably) by going to Integer. However, unless you have a huge number of these objects, that space savings will be minimal, and unless you've actually seen numbers in a profiler, it's pointless to speculate.

Set Java Object with Java Long Object from JNI

Hi,
i am getting crazy with the jni...
in Java i have the follwoing:
public class blabla{
Object myObject;
i chose Object cause the return value from native is not known
in case for a long value i handle it like this :
//get the Long class
jclass LongCls = env->FindClass("Ljava/lang/Long;");
jmethodID jmid = env->GetMethodID(LongCls, "<init>","(J)V");
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jfid = env->GetFieldID(jclazz, "myObject", "Ljava/lang/Object;");
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Java is shown that the myObject contains a Long Object but the long value of the Long Object is totally wrong and doesnt equal to the long value which has been set.But setting the value works fine- any ideas or solutions?
Thank you!

charliess wrote:
sometimes i really wonder about the answers in this forum - until now i got not one answer that helps me, even i tried to write down the problem very detailed...
Sometimes I wonder about people who jump onto a site and immediately assume that
1. They are the most important person in the world
2. That they deserved the absolute undivided attention of absolute everyone.
3. That everyone should be absolutely polite to them and provide them with perfect answers.
4. Feel free to denigrate and posit their own opinion on everything while ignoring anything else that anyone else says.
5. Expect that everyone else should understand their poorly worded questions.
Myself I find such individuals extremely amusing. Although they seldom stick around long here. At least not under their original alias.
plaz tel me how to realise your error checking?example plz
You start by having at least a basic understanding of C/C++ and java.
Then you read the JNI documents, all of them, for each method that you are using.
Then you write code such that it actually reflects the documents. For example you check return types. And probably deal with the possibility that JNI methods might throw exceptions.
as far as i know the jni methods like getfieldids and so on throw exceptions other like stObject dont do that the just return nothing
i can see all exceptions in my Java console thats not the Problem, setting the Long Object does not throwing a exception btw->
Myself I wouldn't expect that a JNI exception would show in the java console. Could I suppose though.
However nothing so far would suggest that an exception is being thrown. That however doesn't alter the fact that you must still write the code such that it could happen.
is it possible in general to set an java Long Object created in C(native) into a Object type (Object) overgiven as parameter in my JNI function with the setObject method?
Is it possible that you could actually follow my previous request and create some code that actually runs instead of cut and pasting whatever you feel like?
plz answer also with code and examples i did the same for you...No you didn't. You posted something which would not compile and quite possibly doesn't represent your actual code at all.
And please note that we do not get paid to do this. If you want to pay someone to solve your problem then there are sites for that.
Paying someone allows you to make all sorts of demands. The more you pay the more people will put up with.
If you don't want to pay and do in fact want free answers then it will probably be in your interest to
1. Be polite
2. Answer the questions that have been asked of you.

How can I cache an object for unlimited time or for ever.

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<expiry-delay system-property="tangosol.coherence.zerostage.expiry.delay">XXXms</expiry-delay>
<flush-delay system-property="tangosol.coherence.zerostage.flush.delay">XXXms</flush-delay>
thanks a lot in advance.

Hi Suhas,
If you look in the documentation http://download.oracle.com/docs/cd/E14526_01/coh.350/e14509/toc.htm and more specifically here http://download.oracle.com/docs/cd/E14526_01/coh.350/e14509/appcacheelements.htm#BABDHGHJ you will see the explination for the two configuration items you mention.
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JK

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thanks for listening

Hi 398287,
Sorry but I can't help you, based on the [lack of] information you have provided. Perhaps if you would provide the following details, I may be able to help you:
1. Complete error message (and stack trace).
2. The part of your code that you think is causing the problem.
3. Environment details (Oracle version, java version, platform, etc.)
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Click in your page where you want the SWF to go, then select
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I have a need to store a large collection of object associated with one key in the cache. And updates to the cache will happen with one of the object in the collection.
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Regards,
Dimitri Attachment: Main.java (*To use this attachment you will need to rename 295.bin to Main.java after the download is complete.)

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Donald,
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Hey,
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null

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