 - ***System properties*** are set on the Java command line using the `-Dpropertyname=value` syntax. They can also be added at runtime
   using [`System.setProperty(String key, String value)`][1] or via the various
   [`System.getProperties().load()`][2] methods.  
  To get a specific *system property* you can use [`System.getProperty(String key)`][3] or [`System.getProperty(String key, String def)`][4].

 - ***Environment variables*** are set in the OS, e.g. in Linux `export HOME=/Users/myusername` or on Windows `SET WINDIR=C:\Windows` etc,
   and, unlike properties, may *not* be set at runtime.  
  To get a specific *environment variable* you can use [`System.getenv(String name)`][5].

  [1]: http://docs.oracle.com/javase/8/docs/api/java/lang/System.html#setProperty-java.lang.String-java.lang.String-
  [2]: http://docs.oracle.com/javase/8/docs/api/java/util/Properties.html#load-java.io.InputStream-
  [3]: http://docs.oracle.com/javase/8/docs/api/java/lang/System.html#getProperty-java.lang.String-
  [4]: http://docs.oracle.com/javase/8/docs/api/java/lang/System.html#getProperty-java.lang.String-java.lang.String-
  [5]: http://docs.oracle.com/javase/8/docs/api/java/lang/System.html#getenv-java.lang.String-

I think the difference between the two boils down to access. Environment variables are accessible by any process and Java system properties are only accessible by the process they are added to.

Also as Bohemian stated, env variables are set in the OS (however they &#39;can&#39; be set through Java) and system properties are passed as command line options or set via [`setProperty()`][1].


  [1]: http://docs.oracle.com/javase/6/docs/api/java/util/Properties.html#setProperty%28java.lang.String,%20java.lang.String%29

I am trying to &quot;decode&quot; this following Base64 string:

&gt; OBFZDTcPCxlCKhdXCQ0kMQhKPh9uIgYIAQxALBtZAwUeOzcdcUEeW0dMO1kbPElWCV1ISFFKZ0kdWFlLAURPZhEFQVseXVtPOUUICVhMAzcfZ14AVEdIVVgfAUIBWVpOUlAeaUVMXFlKIy9rGUN0VF08Oz1POxFfTCcVFw1LMQNbBQYWAQ==

This is what I know about the string itself:

1. The original string is first passed through the following code:

        private static string m000493(string p0, string p1)
        {
            StringBuilder builder = new StringBuilder(p0);
            StringBuilder builder2 = new StringBuilder(p1);
            StringBuilder builder3 = new StringBuilder(p0.Length);
            int num = 0;
        Label_0084:
            while (num &lt; builder.Length)
            {
                int num2 = 0;
                while (num2 &lt; p1.Length)
                {
                    if ((num == builder.Length) || (num2 == builder2.Length))
                    {
                        MessageBox.Show(&quot;EH?&quot;);
                        goto Label_0084;
                    }
                    char ch = builder[num];
                    char ch2 = builder2[num2];
                    ch = (char)(ch ^ ch2);
                    builder3.Append(ch);
                    num2++;
                    num++;
                }
            }
            return m0001cd(builder3.ToString());
        }
The `p1` part in the code is supposed to be the string &quot;`_p0lizei.`&quot;.

2. It is then converted to a Base64 string by the following code:

        private static string m0001cd(string p0)
        {
            string str2;
            try
            {
                byte[] buffer = new byte[p0.Length];
                str2 = Convert.ToBase64String(Encoding.UTF8.GetBytes(p0));
            }
            catch (Exception exception)
            {
                throw new Exception(&quot;Error in base64Encode&quot; + exception.Message);
            }
            return str2;
        }

The question is, how do I decode the Base64 string so that I can find out what the original string is?

How do I decode a base64 encoded string?

Quite often, Git and [Ruby on Rails][1] looks like magic... such as in the [first chapter of Ruby on Rails 3 Tutorial book][2], it talks about Git:

    git remote add origin git@github.com:peter/first_app.git
    git push origin master

And it pretty much says &quot;it just works&quot; without saying too much about what they are and start talking about branching.  Searching on the Internet shows that `git remote add` is to add a &quot;short name&quot;, such as `origin`, and it can be any name as well, which is like an alias to a URL.

And `origin` is the usual path of where the remote repository points to (in http://git-scm.com/book/en/Git-Basics-Working-with-Remotes under &quot;Adding Remote Repositories&quot;).

So why is the URL not `git://git@github.com/peter/first_app.git`, but in the other syntax -- what syntax is it?  Why must it end with `.git`?   I tried not using `.git` at the end and it works too.  If not `.git`, what else can it be?  The `git` in `git@github.com` seems to be a user account on the Git server?

Also, why does it need to be so verbose to use `git push origin master`?  Can&#39;t the default be origin and master?  I found that the first time, the `origin master` is needed, but after a small edit and commit, then `git push` is all it needs (no need `origin master`).  Can somebody who knows what is going on give some details?

Sometimes it feels like a lot of magic without explanation... and sometimes the person using it is so confident and when asked why, can&#39;t explain it, and respond with something like &quot;that&#39;s the way it is&quot;.  Sometimes very practical and pragmatic.  It is not bad to be practical, but probably not practical to the point to not know what is going on.

  [1]: https://en.wikipedia.org/wiki/Ruby_on_Rails
  [2]: http://ruby.railstutorial.org/chapters/beginning#sec:version_control




What is &quot;git remote add ...&quot; and &quot;git push origin master&quot;?

What&#39;s the difference between system properties [System.getProperties()][1] and environment variables [System.getenv()][2] in a JVM?


  [1]: http://download.oracle.com/javase/6/docs/api/java/lang/System.html#getProperties%28%29
  [2]: http://download.oracle.com/javase/6/docs/api/java/lang/System.html#getenv%28%29

Java system properties and environment variables

<p>What's the difference between system properties <a href="http://download.oracle.com/javase/6/docs/api/java/lang/System.html#getProperties%28%29" target="_blank" rel="noopener noreferrer">System.getProperties()</a> and environment variables <a href="http://download.oracle.com/javase/6/docs/api/java/lang/System.html#getenv%28%29" target="_blank" rel="noopener noreferrer">System.getenv()</a> in a JVM?</p>


I&#39;ve faced an issue when I&#39;m trying to get the user input using `Scanner`:

    import java.util.Scanner;
    
    public class Main
    {
    	public static Scanner input = new Scanner(System.in);
    	public static void main(String[] args)
    	{
    		System.out.print(&quot;Insert a number: &quot;);
    		int number = input.nextInt();
    		System.out.print(&quot;Text1: &quot;);
    		String text1 = input.nextLine();
    		System.out.print(&quot;Text2: &quot;);
    		String text2 = input.nextLine();
    	}
    }

Output:

    Insert a number: 55
    Text1: Text2: Hi there!

As you can see, the program skipped `String text1 = input.nextLine();`. What is the problem here? and how to solve this issue?


Scanner issue when using nextLine after nextXXX

Is it possible for me to convert a `String` to an equivalent value in an `Enumeration`, using Java.

I can of course do this with a large `if-else` statement, but I would like to avoid this if possible.

Given this documentation:

http://download.oracle.com/javase/1.4.2/docs/api/java/util/Enumeration.html

I am not too hopeful that this is possible without ifs or a case statement.

Convert String to equivalent Enum value

I have trouble understanding when hibernate hits the second level cache and when does it invalidate the cache.

This is what I currently understand:

 - Second level cache stores entities between sessions, scope is the SessionFactory
 - You have to tell which entities to cache, no entity will get cached by default
 - Query cache stores results of queries in the cache.

What I don&#39;t understand is 
 
- When does hibernate hit this cache? 
- Let&#39;s say I&#39;ve set up the second level cache but not the query caching. I want to cache my customers, there&#39;s 50000 of them. In what ways can I retrieve the customers from the cache? 
- I assume I can get them by id from cache. That would be easy but also not worthy of caching. But what if I want to do some calculation with all my customers. Let&#39;s say I want to show a list of the customers then how would I access them? 
- How would I get all my customers if query caching is disabled? 
- What would happen if someone updated one of the customers? 
 - Would that customer get invalidated in the cache or would all customers get invalidated? 

Or am I thinking caching totally wrong? What would be more appropriate uses of second level cache in that case? The hibernate documentation is not at all clear how the cache works in reality. There are only instructions on how to get it set up.

**Update:**
So I&#39;ve come to understand that second level cache(without query cache) would be good for loading data by id&#39;s. For example I have user object that I want to check for permissions in every request in a web application. Would this be a good case to reduce database access by caching the user in the second level cache? Like I would store the user id in the session or wherever and when I need to check for permissions I would load the user by it&#39;s id and check permissions.



When and how to use hibernate second level cache?

    class Test {
    	public static void main(String...args) {
    		String s1 = &quot;Good&quot;;
    		s1 = s1 + &quot;morning&quot;;
    		System.out.println(s1.intern());
    		String s2 = &quot;Goodmorning&quot;;
    		if (s1 == s2) {
    			System.out.println(&quot;both are equal&quot;);
    		}
    	}
    }

This code produces different outputs in Java 6 and Java 7.
In Java 6 the `s1==s2` condition returns `false` and in Java 7 the `s1==s2` returns `true`. Why?

Why does this program produces different output in Java 6 and Java 7?

intern() behaving differently in Java 6 and Java 7

I am using `&lt;error-page&gt;` element in *web.xml* to specify the friendly error page when user encounters a certain error such as error with code of 404:
&lt;!-- langusge: lang-xml --&gt;

    &lt;error-page&gt;
            &lt;error-code&gt;404&lt;/error-code&gt;
            &lt;location&gt;/Error404.html&lt;/location&gt;
    &lt;/error-page&gt;


However, I want that if the user does not meet any error code specified in `&lt;error-page&gt;`, he or she should see a default error page. How can I do that using the &lt;error-page&gt; element in the *web.xml*?

How to specify the default error page in web.xml?

If a variable is declared as `public static varName;`, then I can access it from anywhere as `ClassName.varName`. I am also aware that static members are shared by all instances of a class and are not reallocated in each instance.

Is declaring a variable as `private static varName;` any different from declaring a variable `private varName;`?

In both cases it cannot be accessed as `ClassName.varName` or as `ClassInstance.varName` from any other class.

Does declaring the variable as static give it other special properties?

What is the use of a private static variable in Java?

I have a `click` event that is triggered from another place automatically for the first time. My problem is that it runs too soon, since the required variables are still being defined by Flash and web services. So right now I have:

    (function ($) {
        $(window).load(function(){
            setTimeout(function(){
                $(&#39;a.play&#39;).trigger(&quot;click&quot;);
            }, 5000);
        });
    })(jQuery);

The problem is that 5 seconds for a person with a slow internet connection could be too fast and vice versa, for a person with a fast internet connection, it&#39;s too slow.

So how should I do the delay or timeout until `someVariable` is defined?

While variable is not defined - wait

I have a makefile, which includes several other makefiles, which in turn all add to a variable like this:

    VAR := Something SomethingElse
    VAR += SomeOtherThing
    
    (...)

Now I wish to remove `SomethingElse` from the `VAR` variable. What do I put in place of `(...)` to do this?

I am using GNU Make, and a GNU Make specific solution will be fine.

Remove item from a Makefile variable?

I&#39;m trying to access a class constant in one of my classes:

    const MY_CONST = &quot;value&quot;;

If I have a variable which holds the name of this constant like this:

    $myVar = &quot;MY_CONST&quot;;

Can I access the value of MY_CONST somehow?

    self::$myVar

does not work obviously because it is for static properties.
Variable variables does not work either.

Accessing a class constant using a simple variable which contains the name of the constant

I need to use something similar to php&#39;s isset function. I know php and java are EXTREMELY different but php is my only basis of previous knowledge on something similar to programming. Is there some kind of method that would return a boolean value for whether or not an instance variable had been initialized or not. For example...

    if(box.isset()) {
      box.removeFromCanvas();
    }

So far I&#39;ve had this problem where I am getting a run-time error when my program is trying to hide or remove an object that hasn&#39;t been constructed yet.

Java check to see if a variable has been initialized

&gt; **Possible Duplicate:**  
&gt; [javascript object, access variable property name?](https://stackoverflow.com/questions/4255472/javascript-object-access-variable-property-name)  

&lt;!-- End of automatically inserted text --&gt;

Trying to get more advanced in my JS...

I have a custom object:

    Object myObject = new Object();

    myObject.thing = anythingHere;


I would like to be able to retrieve a custom objects property by passing in a string... eg:
    
    var propertyString = &#39;thing&#39;;
    alert(myObject.propertyString);

I can&#39;t quite figure that out. I&#39;ve looked at a number of tutorials for custom objects - but nothing shows how to get properties that I don&#39;t know the names of... Also - I would like to avoid looping through all properties if possible...

Thanks!!!

Getting a Custom Objects properties by string var

I am using [this script][1] to make a style object of all the inherited, etc. styles.

    var style = css($(this));
    alert (style.width);
    alert (style.text-align);

With the following, the first alert will work fine, but the second one doesn&#39;t... it&#39;s interpreting the `-` as a minus I assume. The debugger says &#39;uncaught reference error&#39;. I can&#39;t put quotes around it, though, because it isn&#39;t a string. So how do I use this object property?

  [1]: https://stackoverflow.com/questions/754607/can-jquery-get-all-css-styles-associated-with-an-element/5830517#5830517






How do I reference a JavaScript object property with a hyphen in it?

I&#39;ve run into a unique situation that I have so far been unable to find a solution for: dynamically assigning a value to a CSS style.  I know how to use jQuery to assign width, height, etc. to an element, but what I&#39;m trying to do is actually change the value defined in the stylesheet so that the dynamically-created value can be assigned to multiple elements.  

What I&#39;m building is a slideshow of images that occupy the full viewport, recalculating the image&#39;s width, height, and left properties on resize so that the image is always centered, favors width over height, except when the viewport is taller than it is wide (resizing does not reload the page, just fires a function to resize the image).  

I have successfully been able to get it to work on one image, and now I&#39;m trying to determine the best way to assign those property values to all images in the slideshow without having to specify those three things individually for every image.  

My Question:
------------

Can the values of properties in a class be modified on the fly?  I&#39;m sure the answer is out there, I&#39;m probably just not using the correct terminology in my searches.  Hope I did a good job of describing the problem.  TIA.

Modifying CSS class property values on the fly with JavaScript / jQuery

I have seen two ways of detecting whether a UA implements a specific JS property: `if(object.property)` and `if(&#39;property&#39; in object)`.

I would like to hear opinions on which is better, and most importantly, why. Is one unequivocally better than the other? Are there more than just these two ways to do object property detection? Please cover browser support, pitfalls, execution speed, and such like, rather than aesthetics.

**Edit:**  Readers are encouraged to run the tests at [jsperf.com/object-detection][1]

[1]: http://jsperf.com/object-detection/6

JavaScript object detection: dot syntax versus &#39;in&#39; keyword

When I write code like this

    [XmlIgnore]
    [NonSerialized]
    public List&lt;string&gt; paramFiles { get; set; }

I get the following error:

    Attribute &#39;NonSerialized&#39; is not valid on this declaration type.
    It is only valid on &#39;field&#39; declarations.

&lt;br&gt;
If I write

    [field: NonSerialized]

I get the following warning

    &#39;field&#39; is not a valid attribute location for this declaration.
    Valid attribute locations for this declaration are &#39;property&#39;.
    All attributes in this block will be ignored.

&lt;br&gt;
If I write

    [property: NonSerialized]

I get the following error (again):

    Attribute &#39;NonSerialized&#39; is not valid on this declaration type.
    It is only valid on &#39;field&#39; declarations.

&lt;br&gt;
How can I use `[NonSerialized]` on a property?

NonSerialized on property

I had entered:

    * 22 * * * test &gt; /dev/null
However, I am being notified via email that this is running every minute.
I am confused I guess because I thought this was correct for what I am wanting.


How to run cron once, daily at 10pm

I am working in a lab where we are running Linux (Debian and Ubuntu). Usernames and group names are handled by NIS and yp. We have some common users that everybody has access to that run the experiments and then we each have our own users in addition there is a common group that we are all a member of.

How can I make such that all files and directories on the shared `/home/` drive (NFS) is read/write(/executable) by user/group? Basically what I want is

    chmod -R 664 /home
    chgrp -R commongroup /home

or equivalently `umask 0002`.

But running the above commands only fixes the current files in the folders and umask only works for single users and has to be run every time a user logs in ie. in the `.bashrc` file (and will this work for changes mode via gnome?). Is there a system wide command or setting that I could use to make sure that our commongroup has write access to the common files?

How to set system wide umask?

It is possible to run an external command by three PHP functions of

    system();
    exec();
    shell_exec();

but what are their differences? In spite of their specific applications, in most cases, the can be equally used. I am curious to know which is preferred one when they can be equally used. For example, for unzipping a file or compressing a folder (with tar command), which one is preferred (probably from performance point of view)?

**UPDATE:** In another question, I found a very useful **[link][1]** describing different aspects for these functions. I share the link here, as other may use to better understand security issues and other aspects.


  [1]: http://web.archive.org/web/20130809032648/http://chipmunkninja.com/Program-Execution-in-PHP%3A-exec-m@

What are the differences of system(), exec() and shell_exec() in PHP?

I am executing the following command in R :

    system(&quot;ls &quot;)

I need to store the output of the above command in some R variable.
Is there a way to do the same??

store output of system command into a variable in r

Im working with the programming language R now.
I have a vector:

    a &lt;- c(&quot;aa&quot;, &quot;bb&quot;, &quot;cc&quot;)
And I want to paste these to a system command, I&#39;m trying it this way now:

    args &lt;- paste(a, sep=&quot; &quot;)
    system(paste(&quot;command&quot;,args, sep=&quot; &quot;))

But now I&#39;m only getting the arguments aa, and I want the arguments aa, bb and cc...

Anyone knows what I&#39;m doing wrong?

Convert R vector to string vector of 1 element

It would be helpful if someone can illustrate this with a simple example?

Also, where would it be useful to use `parent.frame()` instead of `parent.env()` and vice versa.



What is the difference between parent.frame() and parent.env() in R; how do they differ in call by reference?

When I run:
C:\Users\ashahria\Downloads&gt;java -jar schemaSpy_5.0.0.jar

I get the error below. What is wrong? How can I fix it?

&gt;Error: Registry key &#39;Software\JavaSoft\Java Runtime Environment&#39;\CurrentVersion&#39;
&gt;
&gt;has value &#39;1.5&#39;, but &#39;1.7&#39; is required.&lt;br/&gt;
&gt;Error: could not find java.dll&lt;br/&gt;
&gt;Error: Could not find Java SE Runtime Environment.

Error: Registry key &#39;Software\JavaSoft\Java Runtime Environment&#39;\CurrentVersion&#39;?

I am using seed.rb to populate both my development and production database. I usually populate the first with dummy data and the latter with the real minimal data that my app needs to run (e.g. the first user and so on).

How can I specify in seed.rb for what environment each data is?

Given that I know &quot;group&quot; to be a Gemfile method, I&#39;d like to achieve the same behavior for seed.rb.

E.g. I&#39;d like to write something like this in my seed.rb:

    group :development do 
      # development specific seeding code
    end

    group :production do 
      # production specific seeding code
    end

    # non-specific seeding code (it always runs) 

This to be able to call both the development-specific and the non-specific code with

    $ rake db:seed

And to call both the production-specific and the non-specific code with:

    $ rake db:seed RAILS_ENV=production 


Thank you

How to use seed.rb to selectively populate development and/or production databases?

I&#39;m looking for something like `git list-path` printing the
path of the associated repository (the `.git` directory).

A bit of background: I have set up git version control on quite a few of my
projects/folders.  Some of them are nested, so one directory with echo own repository is a subfolder to another directory tracked with another repository. 

 E.g. in my home directory (`~`) I use git to track my dot files, but
in folder `~/photo/meta-mix/` I have another project I track with a
separate repository. Now, say,I have set up another project in directory
`~/photo/meta-match/`, but I don&#39;t know anymore whether it has its own
repository. So I want to find out whether this directory is version
controlled and where its repository is.

How can I do this with a git command? `git status` can give me 

    nothing to commit

in *both* cases, when `~/photo/meta-match/` has its own repository or when it just refers to the repository of `~`. 

How to find the path of the local git repository when I am possibly in a subdirectory

How is it possible to change the default shell? The `env` command currently says:

    SHELL=/bin/tcsh

and I want to change that to Bash.


Content Type	Original Author	Original Content on Stackoverflow
Question	Praveen Sripati	View Question on Stackoverflow
Solution 1 - Java	Bohemian	View Answer on Stackoverflow
Solution 2 - Java	Jake Dempsey	View Answer on Stackoverflow

Java system properties and environment variables

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

What is "git remote add ..." and "git push origin master"?

How do I decode a base64 encoded string?

Attributions