Why java objects on heap

Hi,
Why the java architecture is such that all the java objects are created on heap. If in certain cases they are allowed to be created on stack then i think the load on garbage collector can be reduced.
Just for curiosity I want to know this.
Thanking you.
- Jaydipsinh Narolia.

A wild stab in the dark...
1) They just didn't think about it.
2) A stack object would imply that there was at least an implicit destructor. But that couldn't be used in heap objects so stack objects couldn't be used.

Similar Messages

Y in java objects are created on heap only and not on stack ??

Hi ,
I need a answer to the question " why all the objects are created on heap only in java and not on stack " ?
In java a object is created when we specify new i.e. for example,
consider the following cases.
1.
Vector v = new Vector();
here object is created and the reference to this object is assigned to variable v. okie.
2.
when i write something like
Vector vec ;
Here i am creating reference variable for Vector. No object is created and no seperate memory is allocated for it. Reference variablesa are stored along with other primitive variables on the java stack.
My question is, in C++ by writing case 2 i can create an object and it is creating this object on stack. So why in java object is not created on stack while i do like this ? Why in java objects are created on heap only ?
If my question is out of interest of this forum i apologize for it. But if somebody can throw some light on it, it would be of great help.
Cheers !!
Dipesh

Hi
I asked this question just to understand how compiler and jvm cud have been designed......i.e. to know the philosophy behind designing language.......
now what i cud surmise is that if objects were to be stored in stack then on calling garbage colllector , it may delete some unused obj and unreferenced object(unreachable object) and this in turn may give rise to non-contagious areas in stack, thus nullifying the garbage collector's objective of freeing the the memory. Again deallocating that intersperse spaces into one free block of space will be bit troublesome task.....
So considering above factor the designer of jvm and java compiler have opted for storing objects on heap rather than stack.....
If u have something to say bout this.......pls go ahead.......
Cheers !!
Dipesh

Y in java objects are created on heap only n not on stack ?

Hi ,
I need a answer to the question " why all the objects are created on heap only in java and not on stack " ?
In java a object is created when we specify new i.e. for example,
consider the following cases.
1.
Vector v = new Vector();
here object is created and the reference to this object is assigned to variable v. okie.
2.
when i write something like
Vector vec ;
Here i am creating reference variable for Vector. No object is created and no seperate memory is allocated for it. Here this reference is placed on the java stack along with other primitive data types.
My question is, in C++ by writing case 2 i can create an object and it is creating this object on stack. So why in java object is not created on stack while i do like this ? Why in java objects are created on heap only ?
If my question is out of interest of this forum i apologize for it. But if somebody can throw some light on it, it would be of great help.
Cheers !!
Dipesh

Cross post!
http://forum.java.sun.com/thread.jsp?forum=32&thread=260589

Why java is called as true object oriented language?

HI Friends,
Though few oops concepts is not supported , why java is called as truly object oriented language and C++ as not a purely object oriented language???? Please, if any one know , give me the answer.
Thanks to all.

few oops concepts is not supportedwhich concepts?
as far as i know...to be OO, you must supports
encapsulation, abstraction, inheritancxe, composition (aggretration, et all) and polymorphism. Java supports all those comcept..now..Java is a hybrid due to what Jverd has pointed out.
the only pure OO language that i know of is SmallTalk. they have Meta class that can create Class object. and all their primitaives are object.
C# comes close, but their Class are not object.

How to figure out the size of an object - java out of heap memory error

Hi all,
I am using an object that I found in a library that I didn't create so I don't know its internal state or members.
I created a single one of these objects and I call announce() on this object which just sends a UDP announcement over the channel to notify listeners. However, after a message #124,288 I get a java out of heap memory error.
I am wondering if this announce() method is causing the state of the object to grow with every call...it seems unlikely but I want to check to see if it's reserving a growing amount of heap memory without ever allowing it to free.
My question is how can I check how big the object is within my program? I'd like to check, for instance, at every 10,000 messages sent how much memory the object is taking up. Is there a method call for that? Would I have to use some kind of debugger or memory monitor? I would like something easy to use.
Please let me know, and thanks in advance.
Julian

jboolean23 wrote:
Thanks for the quick reply.
I say it's unlikely that the methods I call are filling up heap memory because I have one Message object. This one Message has a myMsg String member. Whenever I want to change the message I call myMsg = "anewstringhere". And then I do myMessageObject.announce(); And for that reason i say I only have one Message object. The only thing added to the heap would be the strings that I replace myMsg with. The old references to myMsg are no longer valid and should be garbage collected..
Unless of course if you are calling intern() on them.
so here's my train of thought (and this isn't what my actual code looks like):
myMessageObject.myMsg = "hello" //creates a string on the heap? I assume this is equivalent to saying myMsg = new String("hello")No they are not the same.
The text literal will be in the intern space. Both code fragments would do that.
The second example would create a second instance of String(). That second instance would be cleaned when no longer referenced. But the literal will not.
Is my thought process correct? You are calling a third party library right so mock it (write a simple replacement that does the minimal correct functionality.) Substitute it in your code. And then run. If it still fails then the problem is in your code. If not then it is either in the library or the way that you use the library.

Is it possible to create the memory for a Java object in C/C++?

Is it possible to have a C/C++ program allocate some memory, then have JNI use that memory for primitive java objects (such an array of bytes) that are passed to Java objects ?
I would like to allocate a region of memory in C++, then give that memory to a Java object (via some kind of JNI type) and have that Java object fill the memory region with data.
My impression from reading the JNI API and the few examples I've looked at is "No", there is a strict boundary between C++ and JNI as regards memory management. There may be serious implications as to why what I'm suggesting is not feasible, I am not enough of a JNI expert to know yet, and would greatly appreciate any input/comment.
Many thanks,
Colm.

No, you cannot. However, writing your JNI code you should not use memory of Local Heap (if it possible). Because Local Heap Memory used also by JVM. I have developed tools that generate C++ wrappers for JNI code. In these wrappers I use mainly Global/Virtual Memory. I also reduce to minimum creation of local/global references, as it is affects to JVM memory use. If you are writing JNI code under MS Windows then you can try my tools that automate JNI code writing:
http://simtel.net/product.php[id]93174[SiteID]simtel.net
http://simtel.net/product.php[id]94368[SiteID]simtel.net
Now I am developing this tool for .Net. In two weeks it will be finished.

Urgent: How to find out the size in bytes of java object

Hi Experts,
We've a requirement that we need to find out the size of a java object at run time, is there a direct java API to get the size of a composite object in memory?
Here is my requirement: We are adding string objects (which is an xml string of considerable size) into a List. After reaching certain size limit (lets say 5MB) of the list i need to put this data into DB as a CLOB. So every time I add a string object to the list, I need to see if the total size of the list exceeds the limit and if yes, flush the results into DB.
I am not sure if java has a direct API for this, if not what is the beast way to do it, it s critical requirement for us.
It would be really great if someone could help us out.
Thank you,
-Shibu.

>
We've a requirement that we need to find out the size of a java object at run time, is there a direct java API to get the size of a composite object in memory?
Here is my requirement: We are adding string objects (which is an xml string of considerable size) into a List. After reaching certain size limit (lets say 5MB) of the list i need to put this data into DB as a CLOB. So every time I add a string object to the list, I need to see if the total size of the list exceeds the limit and if yes, flush the results into DB.
I am not sure if java has a direct API for this, if not what is the beast way to do it, it s critical requirement for us.
It would be really great if someone could help us out.
>
Could you explain your actual requirement a little more fully.
1. Is each individual string a separate XML string? Or is it just a fragment? Why would you just concatenate them together into a CLOB? That won't produce valid XML and it won't let you easily separate the pieces again later. So provide a simple example showing some strings and how you need to manipulate them.
2. Are you using these xml strings in Java at all? Or are you just loading them into the database?
For example if you are just loading them into the database you don't need to create a list. Just create a CLOB in Java and append each string to the CLOB. Before you append each one you can check to see if the new string will put you over your length limit. If it will then you write the CLOB to the database, empty the CLOB and start appending again to the new clob instance.
If you explain what you are really trying to do we might be able to suggest some better ways to do it.

Why java file name and class name are equal

could u explain why java file name and class name are equal in java

The relevant section of the JLS (?7.6):
When packages are stored in a file system (?7.2.1), the host system may choose to enforce the restriction that it is a compile-time error if a type is not found in a file under a name composed of the type name plus an extension (such as .java or .jav) if either of the following is true:
* The type is referred to by code in other compilation units of the package in which the type is declared.
* The type is declared public (and therefore is potentially accessible from code in other packages).
This restriction implies that there must be at most one such type per compilation unit. This restriction makes it easy for a compiler for the Java programming language or an implementation of the Java virtual machine to find a named class within a package; for example, the source code for a public type wet.sprocket.Toad would be found in a file Toad.java in the directory wet/sprocket, and the corresponding object code would be found in the file Toad.class in the same directory.
When packages are stored in a database (?7.2.2), the host system must not impose such restrictions. In practice, many programmers choose to put each class or interface type in its own compilation unit, whether or not it is public or is referred to by code in other compilation units.

Is it possible to send Java Object as parameter to an applet

Is there a way to communicate to the applet using java objects instead of String parameters.
can we do the following while invoking an applet
<applet code=some.class>
<param name=name value=object/>
</applet>
in applet
Object obj = (Object) getParameter("name");
Please le me know if you have any suggestions.
Thanks!

in the applet:
URL url = new URL("mypage.jsp?somearg=somevalue");
URLConnection conn = url.openConnection();
conn.connect();
ObjectInputStream in = new ObjectInputStream(conn.getInputStream());and in the JSP (although servlets would be better for this):
<%@page import="java.io.*, java.util.*"
%><% // This is important... if you are going to use JSP, you can't allow any newlines,
// which is why servlets are better for this type of thing...
String somearg = request.getParameter("somearg");
ObjectOutputStream objOut = new ObjectOutputStream(response.getOutputStream());
objOut.writeObject(someObject);
objOut.flush();
objOut.close();
%>

Sending Custom Java Objects over XML!!

Hello all !
Can anybody please tell me how can I send custom Java Objects through XML? For example we can set attributes for a node using the setAttribute method, it accepts only strings, also the setTextContent method requires text and sets the node's value.Can I some way set my own Java object as the value of a particular node or attach it to the node?
Thanks in advance.

Kami_Pakistan wrote:
So I should rather go for Marshalling or Serialization or is there any other work-around possible?I don't know. You didn't say what you had against text formats. Since all Java objects are composed of primitives when you get right down to the bottom, everything in Java can be serialized as text versions of those primitives. So you're going to have to explain why you think a work-around is necessary at all.

Why java is platform independent ?

what is the meaning of java is platform independent ? is it just because of java code can be run in windows/linux/unix platform ? but then C/C++ also can be run in windows/linux/unix . so why those are not called platform independent ?
why java is called platform independent ?

c/c++ creates object code . similary java creates bytecode . java uses interpreter JVM to execute . similary c/c++ object code also executes in any platform. so where is the real difference ?
the classes do not need to be recompiled for different platforms. what do u mean by this ? ".....classes ( i.e bytecode) dont need recompilation ..." .....ok....but same thing is true for C/C++ object code also !! they also dont need recompilation.
where is the difference ?

Java Object in javascript

How can i call a java object and use it inside javascript?
For example if i instantiate an integer in a java class, i want to pass it to javascript, do some work on it like for example incrementing it, and then i want to return its value.
Can i do this?

why don't you write javascript code using jsp and then pass on the value to javascript variable.

Why java is not 100% oops

Hi, All
recently this question was asked in the interview that why java is not 100 % object oriented.....
plz help me regarding this
thanx inn advance...
Ravi

Many, many reasons. One obvious reason being that Java uses primitives. int, char, double and the rest are not objects.

Why java is giving 'attempting to assign weaker access privileges' error?

Can some one can tell me why java is giving 'attempting to assign weaker access privileges' compile error while compiling Abhishekchild.java ?
The two classes is :
public class Abhishek {
       void asd()
     System.out.println("hello");
          static String a;
          public static void main (String st[])
public class Abhishekchild extends Abhishek {
     private void asd()
     System.out.println("hello");
          static String a;
          public static void main (String st[])
}In my opinion, java compiler is showing the error , as method asd has public visibility in Abhishek. java so
(i)it should be visble to all sub classes of Abhishek.java.
But if we override this function in Abhishekchild.java, and change the visibility to private then it will not be available for child of Abhishekchild.java. But these children are also children of Abhishek.java*, but this violates rule (i).*
So java shows a compilation error.

public class Parent {
     public void asd() {
          System.out.println("Hello");
class Child extends Parent {
     public void asd() {
          System.out.println("Hello from child");
     public static void main(String st[]) {
          Parent parentReference = new Child();
          // The reference 'parentReference' knows about Parent.
          // Parent has a public method asd, so below code looks ok.
          // But if child could set the method to private,
          // invoking the code below, would hit the object Child,
          // where asd() is not accessible - and everything fails.
          // Note - the compile visibility is checked according to
          // the reference, not the object itself.
          parentReference.asd();
}See my comments in the code.
- Roy

The Proper way to go - Passing Serialized Java Objects vs. Web Services?

The team which I am apart of in our little "community" is trying to convince some "others" (management) that we should not use web services to communicate (move large data) within the same application (allbeit a huge application spanning across many servers).
Furthermore these "others" are trying to tell us that in this same application when two small apps. inside of this large app. are both java we should not communicate via serialized java objects but instead we should use Web Services and XML. We are trying to convince them that the simplest way is best.
They have asked us to provide them with proof that passing serialized java objects back and forth between two smaller java applications inside of a larger one is an Industry Standard. Can anyone help either straighten my fellow workers and I out or help us convince the "others" of the proper way to go?

When I was a consultant we always gave the client what they wanted. Even if it was the wrong choice. Suck it up.
I'm glad I wasn't one of those customers. Although I agree that a customer is the one who decides what to do, when I pay someone for consultancy, I expect them to consult me. If they know I'm trying to do something that I shouldn't be doing, I expect a good consultant to be able to show me that there's a better way (not just tell me I'm not doing it right, mind you).
We pass a lot of data using XML and we don't have any transmission or processing speed issues.
Then you either have a much better network than our customer did, or we're not talking about the same amounts of data here.
I used the JAX-RPC RI ...
That's cool... our customer was, unfortunately, infected with Borland products, so we had to use BES. The web services on BES were run by Axis.
How large were these messages?
Huge... each element had about 15 attributes, so 1,200 elements would require 19,200 XML nodes (envelope not included). By comparison, the serialized messages weren't even a quarter that size. It's not just about what you send across the network; it's also the effort of parsing XML compared to desrializing Java objects. Our web service wasn't exactly the only process running at the server.
Anyone who understand the fundamental difference between ASCII (XML) and binary (serialized) formats realizes that no web service can possibly achieve the performance of binary Java services. Why do you think that work is being put into binary web services? I'm not saying XML is never a good thing; just that it's not The Holy Grail that a lot of people are making it look like.
http://issues.apache.org/jira/browse/AXIS-688
Ouch.

Why java objects on heap

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