Apparently, `_JAVA_OPTIONS` works on Linux, too:

    $ export _JAVA_OPTIONS=&quot;-Xmx1g&quot;
    $ java -jar jconsole.jar &amp;
    Picked up _JAVA_OPTIONS: -Xmx1g

For Windows users, you can add a system environment variable named _JAVA_OPTIONS, and set the heap size values there. The JVM should be able to grab the virtual machine options from _JAVA_OPTIONS.

This worked for me:

    export _JAVA_OPTIONS=&quot;-Xmx1g&quot;

It&#39;s important that you have no spaces because for me it did not work. I would suggest just copying and pasting. Then I ran:

    java -XshowSettings:vm 

and it will tell you: 

&gt; Picked up _JAVA_OPTIONS: -Xmx1g

what platform are you running?..  
if its unix, maybe adding

    alias java=&#39;java -Xmx1g&#39;  

 to .bashrc (or similar) work

edit: Changing XmX to Xmx

if the platform is Linux, then adding an entry in bash_profile will help.

```
vim ~/.bash_profile
```
then add

```
export _JAVA_OPTIONS=&quot;-Xmx4g&quot; 
```

I am trying to develop on Google App Engine and in the list of the errors displayed in the admin console I always see the following:

&gt; /favicon.ico

i read the documentation , added a new folder called static and added this in my app.yaml:
    
    - url: /favicon.ico
           static_files: static/favicon.ico
           upload: static/favicon.ico

but even now I&#39;m getting the same error...

favicon.ico &quot;not found error&quot; in App Engine

I&#39;m trying to convert some date/times to UTC, which I thought would be dead simple in Python - batteries included, right? Well, it would be simple except that Python (2.6) doesn&#39;t include any tzinfo classes. No problem, a quick search turns up [python-dateutil][1] which should do exactly what I need.

The problem is that I need to install it on Windows. I was able to upack the .tar.gz2 distribution using 7-zip, but now I&#39;m left with a collection of files and no guidance on how to proceed. When I try to run setup.py I get the error &quot;No module named setuptools&quot;.


  [1]: http://pypi.python.org/pypi/python-dateutil

How to install python-dateutil on Windows?

Is there a way that I can set the default heap size for the jvm on my own computer?  I want to set it to 1g, because I&#39;m always running custom programs that always hit the overage point in the default jvm size.

I just dont want to have to remember to type -XmX1g everytime I run my java app from the command line...  

There has to be an admin way to do this right?

increase the java heap size permanently?

Is there a way that I can set the default heap size for the jvm on my own computer? I want to set it to 1g, because I'm always running custom programs that always hit the overage point in the default jvm size.
I just dont want to have to remember to type -XmX1g everytime I run my java app from the command line...
There has to be an admin way to do this right?

I want to convert `String` to `Date` in different formats.

For example, 

I am getting from user,

    String fromDate = &quot;19/05/2009&quot;; // i.e. (dd/MM/yyyy) format

I want to convert this `fromDate` as a Date object of `&quot;yyyy-MM-dd&quot;` format

How can I do this?

Parse String to Date with Different Format in Java

When experiencing networking problems on client machines, I&#39;d like to be able to run a few command lines and email the results of them to myself.

I&#39;ve found Runtime.exec will allow me to execute arbitrary commands, but Collecting the results in a String is more interesting.

I realize I could redirect output to a file, and then read from the file, but my spidey sense is telling me there&#39;s a more elegant way of doing it.

Suggestions?

Capturing stdout when calling Runtime.exec

How can I check if a date is between two other dates, in the case where all three dates are represented by instances of `java.util.Date`?

How can I determine if a date is between two dates in Java?

How do I build a URL or a URI in Java? Is there an idiomatic way, or libraries that easily do this?

I need to allow starting from a request string, parse/change various URL parts (scheme, host, path, query string) and support adding and automatically encoding query parameters.


What is the idiomatic way to compose a URL or URI in Java?

**Note:** This question and most of its answers date to before the release of Java 7. Java 7 provides [Automatic Resource Management][1] functionality for doing this easilly. If you are using Java 7 or later you should advance to [the answer of Ross Johnson][2].

----
What is considered the best, most comprehensive way to close nested streams in Java? For example, consider the setup:

    FileOutputStream fos = new FileOutputStream(...)
    BufferedOS bos = new BufferedOS(fos);
    ObjectOutputStream oos = new ObjectOutputStream(bos);

I understand the close operation needs to be insured (probably by using a finally clause). What I wonder about is, is it necessary to explicitly make sure the nested streams are closed, or is it enough to just make sure to close the outer stream (oos)?

One thing I notice, at least dealing with this specific example, is that the inner streams only seem to throw FileNotFoundExceptions. Which would seem to imply that there&#39;s not technically a need to worry about closing them if they fail.

Here&#39;s what a colleague wrote:

---

Technically, if it were implemented right, closing the outermost
stream (oos) should be enough. But the implementation seems flawed.

Example:
BufferedOutputStream inherits close() from FilterOutputStream, which defines it as:

     155       public void close() throws IOException {
     156           try {
     157             flush();
     158           } catch (IOException ignored) {
     159           }
     160           out.close();
     161       }


However, if flush() throws a runtime exception for some reason, then
out.close() will never be called. So it seems &quot;safest&quot; (but ugly) to
mostly worry about closing FOS, which is keeping the file open.

---

What is considered to be the hands-down best, when-you-absolutely-need-to-be-sure, approach to closing nested streams?

And are there any official Java/Sun docs that deal with this in fine detail?


  [1]: https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
  [2]: https://stackoverflow.com/a/21723193

Correct way to close nested streams and writers in Java

I was reading the answers for this [question][1] and found that there is actually a method called `length()` for `std::string` (I always used `size()`). Is there any specific reason for having this method in `std::string` class? I read both MSDN and CppRefernce, and they seem to indicate that there is no difference between `size()` and `length()`. If that is so, isn&#39;t it making more confusing for the user of the class?


  [1]: https://stackoverflow.com/questions/905355/c-string-length

std::string length() and size() member functions

For example, say I have a class Temp:

    class Temp
    {
        public:
            int function1(int foo) { return 1; }
            void function2(int bar) { foobar = bar; }
    
        private:
            int foobar;
    };

When I create an object of class Temp, how would I calculate how much space it needs, and how is it represented in memory (e.g.| 4 bytes for foobar| 8 bytes for function1 | etc | )


How do you determine the size of an object in C++?

I have a JTable in which I set the column size as follows:

	table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
	table.getColumnModel().getColumn(0).setPreferredWidth(27);
	table.getColumnModel().getColumn(1).setPreferredWidth(120);
	table.getColumnModel().getColumn(2).setPreferredWidth(100);
	table.getColumnModel().getColumn(3).setPreferredWidth(90);
	table.getColumnModel().getColumn(4).setPreferredWidth(90);
	table.getColumnModel().getColumn(6).setPreferredWidth(120);
	table.getColumnModel().getColumn(7).setPreferredWidth(100);
	table.getColumnModel().getColumn(8).setPreferredWidth(95);
	table.getColumnModel().getColumn(9).setPreferredWidth(40);
	table.getColumnModel().getColumn(10).setPreferredWidth(400);

This works fine, but when the table is maximized, I get empty space to the right of the last column. Is it possible to make the last column resize to the end of the window when resized?

I found `AUTO_RESIZE_LAST_COLUMN` property in docs but it does not work.

Edit: `JTable` is in a `JScrollPane` its prefered size is set.

Java JTable setting Column Width

My current situation is: I have to read a file and put the contents into `InputStream`. Afterwards I need to place the contents of the `InputStream` into a byte array which requires (as far as I know) the size of the `InputStream`. Any ideas?

As requested, I will show the input stream that I am creating from an uploaded file

    InputStream uploadedStream = null;
    FileItemFactory factory = new DiskFileItemFactory();
    ServletFileUpload upload = new ServletFileUpload(factory);
    java.util.List items = upload.parseRequest(request);	  
    java.util.Iterator iter = items.iterator();
	  
    while (iter.hasNext()) {
        FileItem item = (FileItem) iter.next();
        if (!item.isFormField()) {
            uploadedStream = item.getInputStream();
            //CHANGE uploadedStreambyte = item.get()
        }
    }
The request is a `HttpServletRequest` object, which is like the `FileItemFactory` and `ServletFileUpload` is from the Apache Commons FileUpload package.

Determine the size of an InputStream

This may have been answered elsewhere but I could not find a suitable response.

I have this code:

    enum enumWizardPage
    {
    	WP_NONE = 0x00,  
    	WP_CMDID = 0x01,	
    	WP_LEAGUES = 0x02,	
    	WP_TEAMS = 0x04,	
    	WP_COMP = 0x08,	
    	WP_DIVISIONS = 0x10,
    	WP_FORMULAS = 0x20,	
    	WP_FINISHED = 0x40,	
    };

Which is legacy and I have to modify it by adding a few new values.
The issue is each value must be a unique bit so they may be OR combined to a bitmap.

The values are set using the #x## hex format, but I&#39;m wondering if this is the max it can store?
What will be the effect, if any, if I change my code to 

    enum enumWizardPage
    {
    	WP_NONE = 0x0000,  
    	WP_CMDID = 0x0001,	
    	WP_LEAGUES = 0x0002,	
    	WP_TEAMS = 0x0004,	
    	WP_COMP = 0x0008,	
    	WP_DIVISIONS = 0x0010,
    	WP_FORMULAS = 0x0020,	
    	WP_FINISHED = 0x0040,	
    };


What is the underlying type of a c++ enum?

In my company there is a coding rule that says, after freeing any memory, reset the variable to `NULL`. For example ...

    void some_func () 
    {
        int *nPtr;
    
        nPtr = malloc (100);
    
        free (nPtr);
        nPtr = NULL;
    
        return;
    }

I feel that, in cases like the code shown above, setting to `NULL` does not have any meaning. Or am I missing something?

If there is no meaning in such cases, I am going to take it up with the &quot;quality team&quot; to remove this coding rule. Please advice.

Setting variable to NULL after free

Typically the default implementation of **`Object.hashCode()`** is some function of the allocated address of the object in memory (though this is not mandated by the *JLS*). Given that the VM shunts objects about in memory, why does the value returned by **`System.identityHashCode()`** never change during the object&#39;s lifetime?

If it is a &quot;one-shot&quot; calculation (the object&#39;s `hashCode` is calculated once and stashed in the object header or something), then does that mean it is possible for two objects to have the same `identityHashCode` (if they happen to be first allocated at the same address in memory)?


How does the JVM ensure that System.identityHashCode() will never change?

Suppose that I define some class:

    class Pixel {
        public:
          Pixel(){ x=0; y=0;};
          int x;
          int y;
    }

Then write some code using it. Why would I do the following?

    Pixel p;
    p.x = 2;
    p.y = 5;

Coming from a Java world I always write:

    Pixel* p = new Pixel();
    p-&gt;x = 2;
    p-&gt;y = 5;

They basically do the same thing, right?
One is on the stack while the other is on the heap, so I&#39;ll have to delete it later on. Is there any fundamental difference between the two? Why should I prefer one over the other?


Why not use pointers for everything in C++?

    int[] myIntegers;
    myIntegers = new int[100];

In the above code, is new int[100] generating the array on the heap? From what I&#39;ve read on CLR via c#, the answer is yes. But what I can&#39;t understand, is what happens to the actual int&#39;s inside the array. As they are value types, I&#39;d guess they&#39;d have to be boxed, as I can, for example, pass myIntegers to other parts of the program and it&#39;d clutter up the stack if they were left on it all the time. Or am I wrong? I&#39;d guess they&#39;d just be boxed and would live on the heap for as long the array existed.

Arrays, heap and stack and value types

I am curious to know what happens when the stack and the heap collide. If anybody has encountered this, please could they explain the scenario.


What Happens When Stack and Heap Collide

Given these two commands

A:

    $ java -Xms10G -Xmx10G myjavacode input.txt

B:

    $ java -Xms5G -Xmx5G myjavacode input.txt

I have two questions:

 1. Since command A reserves more memory with its parameters, will A run faster than B? 
 2. How do `-Xmx` and `-Xms` affect the running process and the output of my program?

Speed tradeoff of Java&#39;s -Xms and -Xmx options

After reading already asked question on the subject and a lot of googling I am still not able to have a clear view of **-Xms** option

My question is: what&#39;s the difference between `java -Xms=512m -Xmx=512m` and `java -Xms=64m -Xmx=512m`?

For now I have the following answer:

The only difference is in the number of garbage collections that will be run during my application&#39;s run and the number of memory allocations. Am I right ?

Here are my reasons for this answer:

Setting the `-Xms` option to `512m` doesn&#39;t result in my application using really `512M` of physical memory after startup. I guess this is related to modern OS virtual memory management and lazy pages allocations. (I noticed that setting `-Xms` to `512M` or to `64M` doesn&#39;t change at all the initial used memory reported either by top on Linux or by the task manager on windows)

Can someone help me to understand the impact of this `Xms` option or point me to links that will help me to understand it?

Thanks in advance

Manu


JVM heap parameters

I need to check if some option that can be passed to JVM is explicitly set or has its default value.

To be more specific:
I need to create one specific thread with higher native stack size than the default one, but in case the user wants to take care of such things by himself by specifying the `-Xss` option I want to create all threads with default stack size (which will be specified by user in -Xss option).

I&#39;ve checked classes like `java.lang.System` and `java.lang.Runtime`, but these aren&#39;t giving me any useful information about VM arguments.

Is there any way to get the information I need?


How to get VM arguments from inside of Java application?

In a shell script, I have set the JAVA_OPTS environment variable (to enable remote debugging and increase memory), and then I execute the jar file as follows:

    export JAVA_OPTS=&quot;-Xdebug -Xrunjdwp:transport=dt_socket,address=8001,server=y,suspend=n -Xms512m -Xmx512m&quot;
    java -jar analyse.jar $*

But it seems there is no effect of the JAVA_OPTS env variable as I cannot connect to remote-debugging and I see no change in memory for the JVM.

What could be the problem?

PS: I cannot use those settings in the `java -jar analyse.jar $*` command because I process command line arguments in the application. 

Running java with JAVA_OPTS env variable has no effect

They are algorithms for the young generation garbage collection. 

The second one (UseParNewGC) gets activated automatically with the concurrent tenured generation garbage collection (see [Java Concurrent and Parallel GC][1]) but, is there a difference between the two parallel algorithms?


  [1]: https://stackoverflow.com/questions/220388/java-concurrent-and-parallel-gc

Content Type	Original Author	Original Content on Stackoverflow
Question	rufus	View Question on Stackoverflow
Solution 1 - Java	Kutzi	View Answer on Stackoverflow
Solution 2 - Java	The Dissonant	View Answer on Stackoverflow
Solution 3 - Java	Justin Chitla	View Answer on Stackoverflow
Solution 4 - Java	Aditya Mukherji	View Answer on Stackoverflow
Solution 5 - Java	mauryaAjay	View Answer on Stackoverflow

increase the java heap size permanently?

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How to install python-dateutil on Windows?

favicon.ico "not found error" in App Engine

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