Where is String object in memory? and why?

I read an article about String, it states:
String str1 = new String("abc");
the String object in the heap,
String str2 = "abc";
then String object will be in data segment?
is the statement true? and why? it's a really interesting question, thx

Thanks you so much for the great article!!
cotton.m!!
I can cheat on my assignment again, haha!
strange
Stepwise Refinement :|
http://forum.java.sun.com//thread.jspa?threadID=5206258

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What is application memory and why does my macbook pro keep running out of it?

what is application memory and why does my macbook pro keep running out of it?

There is excessive swapping of data between physical memory (that is, the memory chips on the logic board) and virtual memory (one or more files on the startup volume.) That activity is relatively slow and causes the whole system to be less responsive. It can happen for two reasons:
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Please note that if the cause is a memory leak, installing more memory will not help. That's likely if you already have more than 4 GB of memory. Tracking down a memory leak can be difficult, and it may come down to a process of elimination.
These instructions are for OS X 10.9 and later. Some details may be slightly different for earlier versions of OS X.
When you notice the swap activity, open the Activity Monitor application and select All Processes from the View menu, if it's not already selected. Select the Memory tab. Click the heading of the Real Mem column in the process table twice to sort the table with the highest value at the top. If you don't see that column, select
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The next suggestion is only for users familiar with the shell. For a more precise, but potentially misleading, test, run the following command:
sudo leaks -nocontext -nostacks process | grep total
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Hana is a Database or Memory and why BW on Hana?

Dear Experts,
I have read few documents regarding Hana and I am confused?
Following is my understanding. Correct me if I am wrong in my understanding?
1. I believe Hana is a database(a different kind of data base with Software and hardware) which stores the data and is very fast.
This Hana Database comprises of both Drive and Ram. Hana's Drive is for storing the Data permanently and Hana's Ram is where the full data from Drive is transferred to Ram and in-memory calculation happens which is very fast.
2. I read that we can have 2 options,a Standalone Hana which reads data from SAP ERP and BW on Hana. Why do we need to have BW on Hana, we can just have Hana itself right, because even without BW its faster?
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Regards
Sam

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Hana have 3 parts of storage:
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2) data: the disk where data is recorded
3) log: the disk where the last transactions are logged and it provides with recovery fails
B) you can have diferents scenearios (I will explain some of them):
BW on hana: it speeds up the data access due to hana technology
suite on hana: ERP and BW on hana
Hana has your DW database: you can use hana like a common database and benefits your organization with the speed of hana.
hope it helps.
this image can show you the diferents scenarios
http://esj.com/articles/2014/07/25/~/media/ECG/VirtualizationReview/Images/2014/07/0714vrm_hana.png

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Thanks you so much for the great article!!
cotton.m!!
I can cheat on my assignment again, haha!
strange
Stepwise Refinement :|
http://forum.java.sun.com//thread.jspa?threadID=5206258

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Hi,
I think so for sending mails you need to configure SMTP Service. Can you check the below link.
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MS

Diffrence between assign a String object by literal and through new

Plz tell me
What is the diffrence between
String x = "surya";
or
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Plz tell me
What is the diffrence between
String x = "surya";
or
String y = new String("Surya");When String x = "surya"; is compiled it is placed in the class's pool of strings. If the same string literal is found elsewhere in the class the same string litteral in the pool is reused ( this is possible since String is immutable ).
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failure = thats the oposite of a hang its where it never starts and is to actually worry about!
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if you are thinking about doing a bios update use this >>Use the MSI HQ Forum USB flasher<<
do not use live update to do the bio's flash as it has a 50/50 chance of bricking the board and the tool above has never had a failure of a flash!

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String object vs String literal

Hi ,
I understand how the string objects are created using new operator and using literal.I also understand how they are stored in memory.All I want to know is that when and why should I create a String object using new and when I should create an object using literal.Is there any specific reason for creating an object using new operator when objects created by both the ways are immutable.
Thanks for the help in advance.
Thanks
Mouli

If you look at the String source code (particularly the constructors) youll learn a lot.
String objects contain a char[] array - and this is the most important part --> a start and length value.
I believe they were attempting to optimize, but this has important implications for developers.
String objects dont necessarily store just the text you see, it may just reference a much bigger char array.
For example, say an API passes you a string that is (lets pretend) a file path (C:\files\java\...\file.txt) that is 1,000,000 characters long.
Now say that you call getFileName() and want to save the filename in a list.
String filename = API.getFile("...").getFileName();
List.add(filename);
Say you do this about 250,000 times.
You estimate that the average file name is 10 chars and ensure there is that much RAM.
You run out of memory. Why?
Well, this example actually happened to me in a real program I was writing to archive drive files.
File.getFilename() returns a substring() of the entire File path.
However, substring is implemented to return a String that just references the original char[] array!
So the really long file path never gets garbage collected!
I was able to fix the program by coding it:
String filename = new String(API.getFile("...").getFileName()); // Copies only the needed chars!
List.add(filename);
So thats really all you need to watch out for. If memory is a concern in your program you want to
make sure you arent referencing large char[] arrays unnecessarily.
But like all things, this is rarely anything to give much thought to.
Only something to remember if you run into problems after coding sensibly and profiling
(or in my case, crashing with OOM exceptions, lol).

How to export & import interface type data object to memory

Hi experts,
My greetings to all.
we have came across a situation where we need to pass interface type data object to memory
and import same from memory.
DATA context TYPE REF TO if_timecontext.
its not possible with regular export statement.
is their any other way to do it?
Thanks in advanced,
Sudhir

Thank you saurabhmani & sandra.
@ saurabhmani : i tried assigning object context to memory (field-symbol) and exporting it to memory, but got runtime error.
@sandra : XML serialization & shared object concept sounds intresting but as you already checked that interface IF_TIMECONTEXT is missing the required IF_SERIALIZABLE_OBJECT interface.
Istead of exporting context data object to memory we tried different approch and it worked out for our requirement
Regards
Sudhir

What's the difference between free memory and inactive memory?

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This is a very informative article:
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Why should I wrap String objects in a class for my HtmlDataTable?

Hi,
Let me describe a basic scenario in which my problem occurs. I have a backing bean and a JSP. The JSP gets a List<String> which is displayed inside a column in an editable HtmlDataTable. Each row in the data table has a UICommandLink that can perform an update to the value in the first column. Hence, the table only has two columns: one input field and one command link.
My problem is this: When I try to execute HtmlDataTable#getRowData() when the command link is pressed, the updated values are not retrieved, but instead the values that have been in the input field before any changes were made. However, if I instead wrap my List objects inside a StringWrapper class (with a String property and appropriate getters and setters) such that I have a List<StringWrapper>, the problem does not occur. Why is this and is there any way to avoid it?
I typed out some code to illustrate my scenario. Example 1 is where the table displays a list of String objects and Example 2 is where the table displays a list of StringWrapper objects.
Example 1: [http://pastebin.com/m2ec5d122|http://pastebin.com/m2ec5d122]
Example 2: [http://pastebin.com/d4e8c3fa3|http://pastebin.com/d4e8c3fa3]
I'll appreciate any feedback, many thanks!

Hi,
Let me describe a basic scenario in which my problem occurs. I have a backing bean and a JSP. The JSP gets a List<String> which is displayed inside a column in an editable HtmlDataTable. Each row in the data table has a UICommandLink that can perform an update to the value in the first column. Hence, the table only has two columns: one input field and one command link.
My problem is this: When I try to execute HtmlDataTable#getRowData() when the command link is pressed, the updated values are not retrieved, but instead the values that have been in the input field before any changes were made. However, if I instead wrap my List objects inside a StringWrapper class (with a String property and appropriate getters and setters) such that I have a List<StringWrapper>, the problem does not occur. Why is this and is there any way to avoid it?
I typed out some code to illustrate my scenario. Example 1 is where the table displays a list of String objects and Example 2 is where the table displays a list of StringWrapper objects.
Example 1: [http://pastebin.com/m2ec5d122|http://pastebin.com/m2ec5d122]
Example 2: [http://pastebin.com/d4e8c3fa3|http://pastebin.com/d4e8c3fa3]
I'll appreciate any feedback, many thanks!

Which is better and why a = new String("AA") or a = "AA"

Hi,
Which is better and why
String a = new String("AA") or
String a = "AA"
Does invoking a construtor waste memory? Please explain in detail.
Thanks in advance
Deepak

> So in case "AA" not there in string pool,
That is not correct.
does new creates "AA" on string pool as well as heap memory?Yes. The literal "AA" points to a pooled String object. The new operator creates a new String object with the same character sequence ("AA"). You can verify this with a little code...
String s = new String("AA");
assert s != "AA";
assert s.equals("AA");
assert s.intern() == "AA";~

Why jvm maintains string pool only for string objects why not for other objects?

why jvm maintains string pool only for string objects why not for other objects? why there is no pool for other objects? what is the specialty of string?

rp0428 wrote:
You might be aware of the fact that String is an immutable object, which means string object once created cannot be manipulated or modified. If we are going for such operation then we will be creating a new string out of that operation.
It's a JVM design-time decision or rather better memory management. In programming it's quite a common case that we will define string with same values multiple times and having a pool to hold these data will be much efficient. Multiple references from program point/ refer to same object/ value.
Please refer these links
What is Java String Pool? | JournalDev
Why String is Immutable in Java ? | Javalobby
Sorry but you are spreading FALSE information. Also, that first article is WRONG - just as OP was wrong.
This is NO SUCH THING as a 'string pool' in Java. There is a CONSTANT pool and that pool can include STRING CONSTANTS.
It has NOTHING to do with immutability - it has to do with CONSTANTS.
Just because a string is immutable does NOT mean it is a CONSTANT. And just because two strings have the exact same sequence of characters does NOT mean they use values from the constant pool.
On the other hand class String offers the .intern() method to ensure that there is only one instance of class String for a certain sequence of characters, and the JVM calls it implicitly for literal strings and compile time string concatination results.
Chapter 3. Lexical Structure
In that sense the OPs question is valid, although the OP uses wrong wording.
And the question is: what makes class Strings special so that it offers interning while other basic types don't.
I don't know the answer.
But in my opinion this is because of the hybrid nature of strings.
In Java we have primitive types (int, float, double...) and Object types (Integer, Float, Double).
The primitive types are consessons to C developers. Without primitive types you could not write simple equiations or comparisons (a = 2+3; if (a==5) ...). [autoboxing has not been there from the beginning...]
The String class is different, almost something of both. You create String literals as you do with primitives (String a = "aString") and you can concatinate strings with the '+' operator. Nevertheless each string is an object.
It should be common knowledge that strings should not be compared with '==' but because of the interning functionality this works surprisingly often.
Since strings are so easy to create and each string is an object the lack ot the interning functionality would cause heavy memory consumption. Just look at your code how often you use the same string literal within your program.
The memory problem is less important for other object types. Either because you create less equal objects of them or the benefit of pointing to the same object is less (eg. because the memory foot print of the individual objects is almost the same as the memory footpint of the references to it needed anyway).
These are my personal thoughts.
Hope this helps.
bye
TPD

Where is String object in memory? and why?

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