Do not miss also `-XX:+JVMCIPrintProperties` for Graal JIT options.

Before dive into sources you can skim over following extracts and find suitable option faster:  

https://chriswhocodes.com/ (OracleJDK 6/7/8/9/10/11/12, OpenJDK 8/9/10/11, Graal CE/EE, OpenJ9, Zing)

http://jvm-options.tech.xebia.fr/

http://www.pingtimeout.fr/2012/05/jvm-options-complete-reference.html

http://stas-blogspot.blogspot.com/2011/07/most-complete-list-of-xx-options-for.html


The best documentation I&#39;ve found is [the source](http://hg.openjdk.java.net/jdk7/jdk7).

I&#39;ve used [this SO Q&amp;A](https://stackoverflow.com/questions/9048254/how-to-compile-an-openjdk-7-debug-build-on-ubuntu-11-10) to create a debug build. With this debug build, you can run `java -XX:+AggressiveOpts -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -XX:+PrintFlagsFinal -XX:+PrintFlagsWithComments -version`.

From the directory with the sources, you could execute (assuming you are using Linux, Cygwin or the like):

    grep -FR &#39;UnlockExperimentalVMOptions&#39; hotspot/

Or, the following (which only looks at `*.cpp` and `*.hpp` files):

    find hotspot/ -name &#39;*.[ch]pp&#39; -exec grep -F &#39;UnlockExperimentalVMOptions&#39; {} +

Then look at the source files. Probably the best reason why there is no one document that describes all options is that some of these options are better left to those who really understand the JVM and the best way to do that is to become intimately familiar with the source code.

So, in the words (almost) of a great [master](https://en.wikipedia.org/wiki/Yoda), `use the source`!


I have a list

    a = [&quot;a&quot;, &quot;b&quot;, &quot;c&quot;, &quot;d&quot;, &quot;e&quot;]

I want to remove elements in this list in a for loop like below:

    for item in a:
        print(item)
        a.remove(item)

But it doesn&#39;t work. What can I do?


How to remove list elements in a for loop in Python?

There are two columns in a MySQL table: `SUBJECT` and `YEAR`. 

I want to generate an alphanumeric unique number which holds the concatenated data from SUBJECT and YEAR.

How can I do this?  Is it possible to use a simple operator like `+`?

MySQL, Concatenate two columns

Found an interesting JVM Flag :

    java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version

It prints hundreds of various options, I never heard about before. 
It also prints default values, that helps diagnose JVM behaviors better.
Another interesting flag is: 

    -XX:+UnlockExperimentalVMOptions

Does anyone knows of any documentation which explains each one of them ?

Print All JVM Flags

Found an interesting JVM Flag :
<pre><code class="hljs language-ruby">java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version
</code></pre>
It prints hundreds of various options, I never heard about before.
It also prints default values, that helps diagnose JVM behaviors better.
Another interesting flag is:
<pre><code class="hljs language-ruby">-XX:+UnlockExperimentalVMOptions
</code></pre>
Does anyone knows of any documentation which explains each one of them ?

Reading the [Java documentation for the ADT List][1] it says:

&gt;The List interface provides four methods for positional (indexed) access to list elements. Lists (like Java arrays) are zero based. Note that these operations may execute in time proportional to the index value for some implementations (the LinkedList class, for example). Thus, iterating over the elements in a list is typically preferable to indexing through it if the caller does not know the implementation.

What exactly does this mean? I don&#39;t understand the conclusion which is drawn.


  [1]: http://docs.oracle.com/javase/7/docs/api/java/util/List.html

Why would iterating over a List be faster than indexing through it?

By suitable, I mean:

 - mature and used extensively
 - rich widget set that renders well
 - idiomatic Scala
 - Got a WYSIWYG-ish but flexible GUI builder
 - standalone API documentation (if a wrapper, it shouldn&#39;t make me refer the parent project in another language)

In no particular order.

Which GUI toolkits satisfy which conditions?



Suitable GUI framework for Scala?

I am doing basic http auth with the `HttpURLConnection` object in Java.

            URL urlUse = new URL(url);
			HttpURLConnection conn = null;
			conn = (HttpURLConnection) urlUse.openConnection();
			conn.setRequestMethod(&quot;GET&quot;);
			conn.setRequestProperty(&quot;Content-length&quot;, &quot;0&quot;);
			conn.setUseCaches(false);
			conn.setAllowUserInteraction(false);
			conn.setConnectTimeout(timeout);
			conn.setReadTimeout(timeout);
			conn.connect();
			
			if(conn.getResponseCode()==201 || conn.getResponseCode()==200)
			{
				success = true;
			}


I am expecting a JSON object, or string data in the format of a valid JSON object, or HTML with simple plain text that is valid JSON. How do I access that from the `HttpURLConnection` after it returns a response?

Parse JSON from HttpURLConnection object

Whenever I call `shutdownNow()` or `shutdown()` it doesn&#39;t shut down. I read of a few threads where it said that shutting down is not guaranteed - can someone provide me a good way of doing it?

How to shutdown an ExecutorService?

I am using slf4j for logging in my application.
I get the purpose of slf4j. I would like to know how to find out which logging-library slf4j is currently binding to. I have log4j in my referenced libraries. I am assuming that slf4j has bound itself to log4j.

What I would like to know is, is there any way to explicitly confirm this binding?

How to find which library slf4j has bound itself to?

Is there any advantage of using `{}` instead of string concatenation?

An example from slf4j


    logger.debug(&quot;Temperature set to {}. Old temperature was {}.&quot;, t, oldT);


instead of

    logger.debug(&quot;Temperature set to&quot;+ t + &quot;. Old temperature was &quot; + oldT);

I think it&#39;s about speed optimization because parameters evaluation (and string concatenation) could be avoided in runtime depending on a config file. But only two parameters are possible, then sometimes there is no other choice than string concatenation. Needing views on this issue.

Logger slf4j advantages of formatting with {} instead of string concatenation

I tried to scrub the GCC man page for this, but still don&#39;t get it, really.

What&#39;s the difference between `-march` and `-mtune` ?

When does one use just `-march`, vs. both? Is it ever possible to just `-mtune`?

GCC: how is march different from mtune?

Which of the following techniques is the best option for dividing an integer by 2 and why?

Technique 1:

    x = x &gt;&gt; 1;

Technique 2:

    x = x / 2;

Here `x` is an integer.

Which is better option to use for dividing an integer number by 2?

The title of the question might be a bit strange, but the thing is that, as far as I know, there is nothing that speaks against tail call optimization at all. However, while browsing open source projects, I already came across a few functions that actively try to stop the compiler from doing a tail call optimization, for example the implementation of [CFRunLoopRef](http://opensource.apple.com/source/CF/CF-635.21/CFRunLoop.c) which is full of such *hacks*. For example:

    static void __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__() __attribute__((noinline));
    static void __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__(CFRunLoopObserverCallBack func, CFRunLoopObserverRef observer, CFRunLoopActivity activity, void *info) {
        if (func) {
            func(observer, activity, info);
        }
        getpid(); // thwart tail-call optimization
    }

I would love to know why this is seemingly so important, and are there any cases were I as a *normal* developer should keep this is mind too? Eg. are there common pitfalls with tail call optimization?

Why would code actively try to prevent tail-call optimization?

&gt; **Possible Duplicate:**  
&gt; [Flattening a shallow list in Python](https://stackoverflow.com/questions/406121/flattening-a-shallow-list-in-python)  
&gt; [Flatten (an irregular) list of lists in Python](https://stackoverflow.com/questions/2158395/flatten-an-irregular-list-of-lists-in-python)  

&lt;!-- End of automatically inserted text --&gt;

**EDIT:** The question is not *how* to do it - this has been [discussed][1] in other [questions][2] - the question is, which is the *fastest* method?

I&#39;ve found solutions before, but I&#39;m wondering what the fastest solution is to flatten lists which contain other lists of arbitrary length.

For example:

    [1, 2, [3, 4, [5],[]], [6]]

Would become:

    [1,2,3,4,5,6]

There can be infinitely many levels. Some of the list objects can be strings, which mustn&#39;t be flattened into their sequential characters in the output list.


  [1]: https://stackoverflow.com/questions/406121/flattening-a-shallow-list-in-python
  [2]: https://stackoverflow.com/questions/2158395/flatten-an-irregular-list-of-lists

What is the fastest way to flatten arbitrarily nested lists in Python?

When I use the `print` command, it prints whatever I want and then goes to a different line. For example: 

    print &quot;this should be&quot;; print &quot;on the same line&quot;

Should return: 

&gt; this should be on the same line

but instead returns: 

&gt; this should be  
&gt; on the same line

More precisely I was trying to create a program with `if` that told me whether a number was a 2 or not

    def test2(x):
	    if x == 2:
		    print &quot;Yeah bro, that&#39;s tottaly a two&quot;
	    else:
		    print &quot;Nope, that is not a two. That is a (x)&quot;

But it doesn&#39;t recognise the last `(x)` as the value entered, and rather prints exactly: &quot;(x)&quot; (the letter with the brackets). To make it work I have to write:

    print &quot;Nope, that is not a two. That is a&quot;; print (x)

And if e.g. I enter `test2(3)` that gives:

&gt; Nope, that is not a two, that is a  
&gt; 3

So either I need to make Python recognise my (x) inside a print line as the number; or to print two separate things but on the same line. 

**IMPORTANT NOTE**: I am using **version 2.5.4**

Another note: If I put `print &quot;Thing&quot; , print &quot;Thing2&quot;` it says &quot;Syntax error&quot; on the 2nd print.

Python: avoid new line with print command

Is there a way to widen the display of output in either interactive or script-execution mode?

Specifically, I am using the `describe()` function on a Pandas `DataFrame`.  When the `DataFrame` is five columns (labels) wide, I get the descriptive statistics that I want.  However, if the `DataFrame` has any more columns, the statistics are suppressed and something like this is returned:

```lang-none
&gt;&gt; Index: 8 entries, count to max
&gt;&gt; Data columns:
&gt;&gt; x1          8  non-null values
&gt;&gt; x2          8  non-null values
&gt;&gt; x3          8  non-null values
&gt;&gt; x4          8  non-null values
&gt;&gt; x5          8  non-null values
&gt;&gt; x6          8  non-null values
&gt;&gt; x7          8  non-null values
```

The &quot;8&quot; value is given whether there are 6 or 7 columns.  What does the &quot;8&quot; refer to?

I have already tried dragging the [IDLE][1] window larger, as well as increasing the &quot;Configure IDLE&quot; width options, to no avail.

My purpose in using Pandas and `describe()` is to avoid using a second program like Stata to do basic data manipulation and investigation.

  [1]: https://en.wikipedia.org/wiki/IDLE



How do I expand the output display to see more columns of a Pandas DataFrame?

I have this python program that adds strings to integers:

    a = raw_input(&quot;Enter a: &quot;)
    b = raw_input(&quot;Enter b: &quot;)
    print &quot;a + b as strings: &quot; + a + b
    a = int(a)
    b = int(b)
    c = a + b
    str(c)
    print &quot;a + b as integers: &quot; + c

I get this error:

    Python: TypeError: cannot concatenate &#39;str&#39; and &#39;int&#39; objects

How can I add strings to integers?

Python: TypeError: cannot concatenate &#39;str&#39; and &#39;int&#39; objects

I want to print the looped output to the screen on the same line.

How do I this in the simplest way for Python 3.x

I know this question has been asked for Python 2.7 by using a comma at the end of the line i.e. print I, but I can&#39;t find a solution for Python 3.x.
     
    

    i = 0 
    while i &lt;10:
         i += 1 
         ## print (i) # python 2.7 would be print i,
         print (i) # python 2.7 would be &#39;print i,&#39;

Screen output.

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10

----

What I want to print is: 

    12345678910

New readers visit this link aswell [http://docs.python.org/release/3.0.1/whatsnew/3.0.html](http://docs.python.org/release/3.0.1/whatsnew/3.0.html)

Print new output on same line

I understand the difference between a statement and an expression, and I understand that Python3 turned print() into a function.

However I ran a print() statement surrounded with parenthesis on various Python2.x interpreters and it ran flawlessly, I didn&#39;t even have to import any module.

My question: Is the following code `print(&quot;Hello SO!&quot;)` evaluated as a statement or an expression in Python2.x?

Using print() (the function version) in Python2.x

Is there a way to specify default JVM arguments when I&#39;m running my code from eclipse, rather than specifying the same ones over and over for each run/debug/etc configuration?

How can I specify the default JVM arguments for programs I run from eclipse?

For Sun/Oracle&#39;s JVM, I&#39;ve read that the GC algo divides new generation into one Eden region and two survivor regions. What I&#39;m wondering about is, why two survivor regions and not just one? The algo can keep ping-ponging between Eden and just one survivor region (the way it currently does between two survivor regions); or are there any shortcomings to this approach?

Java GC: why two survivor regions?

Htop on my linux machine shows many &quot;processes&quot; after launching one java program/JVM. I do understand that the JVM runs multiple
threads (for the actual program, for garbage collection, etc). 

But how come htop lists them as multiple processes with different pids. What exactly are those processes?

Htop showing multiple java processes with different pids

I am trying to run a .jar file that was created successfully in Netbeans and I am receiving the following error:

&gt; Error occurred during initialization of VM java.lang.Error: 
&gt; Properties init: Could not determine current working directory. at 
&gt; java.lang.System.initProperties(Native Method) at 
&gt; java.lang.System.initializeSystemClass(System.java:1070) 

The command that I type to run the .jar is 

    java -jar &quot;/path to the dist forlder/EOPPrototype.jar&quot;

My classpath is as follows:

    CLASSPATH=/opt/netbeans-7.1.2/ide/modules/ext/mysql-connector-java-5.1.13-     bin.jar:/h/USERS/local/pagola/NetBeansProjects/mylib/dist/mylib.jar:/h/USERS/local/pagola/NetBeansProjects/EOPPrototype/build/classes:.

What am i missing?


Cannot determine current directory

What does the HotSpot JVM flag `-XX:+UseCompressedOops` do and when should I use it? What sort of performance and memory-usage differences will I see when using it on a 64-bit Java instance (vs. not using it)? 

What does the UseCompressedOops JVM flag do and when should I use it?

I have some heavily instrumented code that makes use of the `log` package. Now it&#39;s come time to turn off the logging, and I can&#39;t determine how to turn off the standard logger.

Have I missed something? Should I be checking a flag before making log calls, or commenting them out in production?

How to disable a log.Logger

Currently I&#39;m starting a new `Activity` and calling `finish` on a current one.

Is there any flag that can be passed to `Intent` that enables finishing current `Activity` without a need to call `finish` manually from code?



Start new Activity and finish current one in Android?

I&#39;m trying to write a script that will check two error flags, and in case one flag (or both) are changed it&#39;ll echo-- error happened. My script:

    my_error_flag=0
    my_error_flag_o=0
    do something.....
    if [[ &quot;$my_error_flag&quot;==&quot;1&quot; || &quot;$my_error_flag_o&quot;==&quot;2&quot; ] || [ &quot;$my_error_flag&quot;=&quot;1&quot; &amp;&amp;     &quot;$my_error_flag_o&quot;=&quot;2&quot; ]]; then
        echo &quot;$my_error_flag&quot;
    else
        echo &quot;no flag&quot;
    fi

Basically, it should be, something along:
    
    if ((a=1 or b=2) or (a=1 and b=2))
      then
         display error
    else
         no error
    fi

The error I get is:

     line 26: conditional binary operator expected
     line 26: syntax error near `]&#39;
     line 26: `if [[ &quot;$my_error_flag&quot;==&quot;1&quot; || &quot;$my_error_flag_o&quot;==&quot;2&quot; ] || [ &quot;$my_error_flag&quot;=&quot;1&quot; &amp;&amp; &quot;$my_error_flag_o&quot;=&quot;2&quot; ]]; then&#39;

Are my brackets messed up?

Bash if statement with multiple conditions throws an error

I am using Enum flags in my application. The Enum can have around 50+ values, so values go up to 2^50. I was just wondering, can I use `Math.Pow(2, variable)` to calculate these?

When I try to do that I get a *constant value* compile-time error. Is there another way, other than calculating these powers of 2 manually and putting it in?

Here&#39;s what I am doing:

    [Flags]
    internal enum RiskStates : long
        {
            None = 0,
            AL = Convert.ToInt64(Math.Pow(2,0)),
            AK = 2,
            AZ = 4,
            AR = 8,
            CA = 16,
            CO = 32,
            CT = 64,
            DC = 128,
            DE = 256,
            FL = 512,
            GA = 1024,
            HI = 2048,
            ID = 4096,
            IL = 8192,
            IN = 16384,
            IA = 32768,
            KS = 65536,
            KY = 131072,
            LA = 262144,
            ME = 524288,
            MD = 1048576,
            MA = 2097152,
            MI = 4194304
    }


Content Type	Original Author	Original Content on Stackoverflow
Question	Sachin Bhansali	View Question on Stackoverflow
Solution 1 - Java	Andriy Plokhotnyuk	View Answer on Stackoverflow
Solution 2 - Java	Dan Cruz	View Answer on Stackoverflow

Print All JVM Flags

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

MySQL, Concatenate two columns

How to remove list elements in a for loop in Python?

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