This means FirstName is null

    &lt;FirstName i:nil=&quot;true&quot; /&gt;


This means FirstName = &quot;&quot;

    &lt;FirstName /&gt;


Assumption made on FirstName is of string type.



Maybe `i:nil` actually means `xsi:nil`, this means that the `FirstName` element is empty, i.e. does not have **any** content -- not even `&quot;&quot;`. It refers to the `nillable` property in XML Schema.





nil is an attribute, defined in the `i` namespace. For this FirstName node, the attribute has the value `true`.

It&#39;s similar to this, just with different names and values:

    &lt;form name=&quot;test&quot;&gt;...

Here, `form` is the name of the node, similar to `FirstName` from your code, and `name` is an attribute with a value of &quot;test&quot;, similar to your attribute `nil` with a value of &quot;true&quot;.

What this means depends on the application reading the xml document.

If I were to venture a guess, I&#39;d say that this looks like part of a xml document defining some kind of schema, and that the FirstName field can have a NULL or `nil` value, meaning empty, or unknown.

### Background:
I am taking a class at my university called &quot;Software Constraints&quot;. In the first lectures we were learning how to build good APIs. 

A good example we got of a really bad API function is the socket `public static void Select(IList checkRead, IList checkWrite, IList checkError, int microseconds);` in C#. The function receives 3 lists of sockets, and destroys them making the user have to clone all the sockets before feeding them into the `Select()`. It also has a timeout (in microseconds) which is an int, that sets the maximum time the server can wait for a socket. The limits of this is +/-35 minutes (because it is an int).

---
### Questions:

 1. How do you define an API as
    &#39;bad&#39;?   
 2. How do you define an
    API as &#39;good&#39;?

---
### Points to consider:
 - Function names that are hard to remember.
 - Function parameters that are hard to understand.
 - Bad documentation.
 - Everything being so interconnected that if you need to change 1 line of code you will actually need to change hundreds of lines in other places.
 - Functions that destroy their arguments.
 - Bad scalability due to &quot;hidden&quot; complexity.
 - It&#39;s required from the user/dev to build wrappers around the API so that it can be used.



How do you define a good or bad API?

What is the significance of the two keywords [Shadows][1] and [Overrides][2]? What they do and for which context is one or the other preferable?

  [1]: http://msdn.microsoft.com/en-us/library/1h3wytf6.aspx
  [2]: http://msdn.microsoft.com/en-us/library/k777kzw1.aspx


&#39;Shadows&#39; vs. &#39;Overrides&#39; in VB.NET

I have an xml and it has nodes with i:nil=&quot;true&quot; in it.  What does that mean?

For example:

    &lt;FirstName i:nil=&quot;true&quot; /&gt;

Does that mean something different than:

    &lt;FirstName /&gt;

If so, what is the difference?

What does i:nil=&quot;true&quot; mean?

I have an xml and it has nodes with i:nil="true" in it. What does that mean?
For example:
<pre><code class="hljs language-ini">&#x3C;FirstName i:nil="true" />
</code></pre>
Does that mean something different than:
<pre><code class="hljs language-php-template">&#x3C;FirstName />
</code></pre>
If so, what is the difference?

&gt; **Possible Duplicate:**  
&gt; [Converting XML to JSON using Python?](https://stackoverflow.com/questions/191536/converting-xml-to-json-using-python)  

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

I&#39;m doing some work on App Engine and I need to convert an XML document being retrieved from a remote server into an equivalent JSON object.

I&#39;m using `xml.dom.minidom` to parse the XML data being returned by `urlfetch`. I&#39;m also trying to use `django.utils.simplejson` to convert the parsed XML document into JSON. I&#39;m completely at a loss as to how to hook the two together. Below is the code I&#39;m tinkering with:

	from xml.dom import minidom
	from django.utils import simplejson as json

	#pseudo code that returns actual xml data as a string from remote server. 
	result = urlfetch.fetch(url,&#39;&#39;,&#39;get&#39;);

	dom = minidom.parseString(result.content)
	json = simplejson.load(dom)

	self.response.out.write(json)



How to convert XML to JSON in Python?

I have to generate a xml file dynamically at runtime. Please help me in generating the below XML file dynamically using PHP.



    &lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;
    &lt;xml&gt;
     &lt;track&gt;
         &lt;path&gt;song1.mp3&lt;/path&gt;
         &lt;title&gt;Track 1 - Track Title&lt;/title&gt;
     &lt;/track&gt;
     &lt;track&gt;
         &lt;path&gt;song2.mp3&lt;/path&gt;
         &lt;title&gt;Track 2 - Track Title&lt;/title&gt;
     &lt;/track&gt;
     &lt;track&gt;
         &lt;path&gt;song3.mp3&lt;/path&gt;
         &lt;title&gt;Track 3 - Track Title&lt;/title&gt;
     &lt;/track&gt;
     &lt;track&gt;
         &lt;path&gt;song4.mp3&lt;/path&gt;
         &lt;title&gt;Track 4 - Track Title&lt;/title&gt;
     &lt;/track&gt;
     &lt;track&gt;
         &lt;path&gt;song5.mp3&lt;/path&gt;
         &lt;title&gt;Track 5 - Track Title&lt;/title&gt;
     &lt;/track&gt;
     &lt;track&gt;
         &lt;path&gt;song6.mp3&lt;/path&gt;
         &lt;title&gt;Track 6 - Track Title&lt;/title&gt;
     &lt;/track&gt;
     &lt;track&gt;
         &lt;path&gt;song7.mp3&lt;/path&gt;
         &lt;title&gt;Track 7 - Track Title&lt;/title&gt;
     &lt;/track&gt;
     &lt;track&gt;
         &lt;path&gt;song8.mp3&lt;/path&gt;
         &lt;title&gt;Track 8 - Track Title&lt;/title&gt;
     &lt;/track&gt;
    
   &lt;/xml&gt;


How to generate XML file dynamically using PHP?

How do I get just the children of an XElement?

I am currently using the XElement.Descendants() function, which returns all levels of XElements, rather than just the child nodes.

What I would really like is an IEnumerable&lt;XElement&gt; of just the children.

Children of XElement

Vim `%` operator jumps to matching parentheses, comment ends and a few other things.  It doesn&#39;t, however, match XML tags (or any other tag, to the best of my knowledge).

What&#39;s the best way to jump to the matching XML tag using Vim?

**Note:**  What I *really* want to do is duplicate a section in an XML file without manually looking for the matching tag.

Jump to matching XML tags in Vim

How can space and tab be represented in an XML tag?

Are there any special characters that can represent them?

Represent space and tab in XML tag?

I appreciate the semantic meaning of a NULL value in a database table, different from both false and the empty string &#39;&#39;.  However, I have often read about performance problems when fields are nullable and been advised to use an empty string in cases where NULL is actually semantically correct.  

What circumstances are appropriate to use nullable fields and NULL values?  What are the trade-offs?  Is it sensible to simply avoid using NULLs altogether and simply use empty strings, false or 0 to indicate the absence of a value?

**UPDATE**

OK - I understand the semantic difference between &#39;&#39; and NULL as well as the (performance-agnostic) circumstances in which NULL is the appropriate field value.  However, let me expand on the hinted performance issue.  This is from the excellent &quot;High Performance MySQL&quot; by Schwartz, Zeitsev et al 
[http://www.borders.co.uk/book/high-performance-mysql-optimization-backups-replication-and-more/857673/][1]:

&gt; It&#39;s harder for MySQL to optimize
&gt; queries that refer to nullable coumns,
&gt; because they make indexes, index
&gt; statistics, and value comparisons more
&gt; complicated.  A nullable column uses
&gt; more storage space and requires
&gt; special processing inside MySQL.  When
&gt; a nullable column is indexed, it
&gt; requires an extra byte per entry and
&gt; can even cause a fixed-size inded
&gt; (such as an index on a single integer
&gt; column) to be converted to a
&gt; variable-sized one in MyISAM.

More here:
[Google books preview][2]

This is quite possibly the definitive answer - I was just looking for second opinions and experience from the front-line.


  [1]: http://www.borders.co.uk/book/high-performance-mysql-optimization-backups-replication-and-more/857673/
  [2]: http://books.google.com/books?id=BL0NNoFPuAQC&amp;pg=PA81&amp;lpg=PA81&amp;dq=%22avoid+null+if+possible%22&amp;source=web&amp;ots=CNSMtvsC4R&amp;sig=Bbp2iSaTdzWpgYhOOcat3aKLuzI&amp;hl=en&amp;sa=X&amp;oi=book_result&amp;resnum=3&amp;ct=result

When to use NULL in MySQL tables

I&#39;m using jQuery and I want to check the existence of an element in my page. I have written following code, but it&#39;s not working:

    if($(&quot;#btext&quot; + i) != null) {
        //alert($(&quot;#btext&quot; + i).text());
    	$(&quot;#btext&quot; + i).text(&quot;Branch &quot; + i);
    }

How do I check the existence of the element?

How to check null objects in jQuery

I&#39;m implementing `compareTo()` method for a simple class such as this (to be able to use `Collections.sort()` and other goodies offered by the Java platform):

    public class Metadata implements Comparable&lt;Metadata&gt; {
        private String name;
        private String value;
    
    // Imagine basic constructor and accessors here
    // Irrelevant parts omitted
    }

I want the *natural ordering* for these objects to be: 1) sorted by name and 2) sorted by value if name is the same; both comparisons should be case-insensitive. For both fields null values are perfectly acceptable, so `compareTo` must not break in these cases. 

The solution that springs to mind is along the lines of the following (I&#39;m using &quot;guard clauses&quot; here while others might prefer a single return point, but that&#39;s beside the point):

    // primarily by name, secondarily by value; null-safe; case-insensitive
    public int compareTo(Metadata other) {
        if (this.name == null &amp;&amp; other.name != null){
            return -1;
        }
        else if (this.name != null &amp;&amp; other.name == null){
            return 1;
        }
        else if (this.name != null &amp;&amp; other.name != null) {
            int result = this.name.compareToIgnoreCase(other.name);
            if (result != 0){
                return result;
            }
        }

        if (this.value == null) {
            return other.value == null ? 0 : -1;
        }
        if (other.value == null){
            return 1;
        }
    
        return this.value.compareToIgnoreCase(other.value);
    }

This does the job, but I&#39;m not perfectly happy with this code. Admittedly it isn&#39;t *very* complex, but is quite verbose and tedious.

The question is, **how would you make this less verbose** (while retaining the functionality)? Feel free to refer to Java standard libraries or Apache Commons if they help. Would the only option to make this (a little) simpler be to implement my own &quot;NullSafeStringComparator&quot;, and apply it for comparing both fields?

**Edits 1-3**: Eddie&#39;s right; fixed the &quot;both names are null&quot; case above

## About the accepted answer 

I asked this question back in 2009, on Java 1.6 of course, and at the time **[the pure JDK solution by Eddie][1]** was my preferred accepted answer. I never got round to changing that until now (2017).

There are also [3rd party library solutions][2]—a 2009 Apache Commons Collections one and a 2013 Guava one, both posted by me—that I did prefer at some point in time.

I now made the clean **[Java 8 solution by Lukasz Wiktor](https://stackoverflow.com/a/23908426/56285)** the accepted answer. That should definitely be preferred if on Java 8, and these days Java 8 should be available to nearly all projects.

  [1]: https://stackoverflow.com/a/481836/56285
  [2]: https://stackoverflow.com/a/500643/56285

How to simplify a null-safe compareTo() implementation?

Is there any way to determine (programatically, of course) if a given pointer is &quot;valid&quot;? Checking for NULL is easy, but what about things like 0x00001234? When trying to dereference this kind of pointer an exception/crash occurs.

A cross-platform method is preferred, but platform-specific (for Windows and Linux) is also ok.

**Update for clarification:**
The problem is not with stale/freed/uninitialized pointers; instead, I&#39;m implementing an API that takes pointers from the caller (like a pointer to a string, a file handle, etc.). The caller can send (in purpose or by mistake) an invalid value as the pointer. How do I prevent a crash?



Testing pointers for validity (C/C++)

In `observeValueForKeyPath:ofObject:change:context:` - why do the docs use `NULL` instead of `nil` when not specifying a context pointer?

NULL vs nil in Objective-C

I have seen `null` elements represented in several ways:

**The element is present with `xsi:nil=&quot;true&quot;`:**

     &lt;book&gt;
         &lt;title&gt;Beowulf&lt;/title&gt;
         &lt;author xsi:nil=&quot;true&quot;/&gt;
     &lt;/book&gt;

**The element is present, but represented as an empty element** (which I believe is wrong since &#39;empty&#39; and `null` are semantically different):

     &lt;book&gt;
         &lt;title&gt;Beowulf&lt;/title&gt;
         &lt;author/&gt;
     &lt;/book&gt;

     &lt;!-- or: --&gt;
     &lt;book&gt;
         &lt;title&gt;Beowulf&lt;/title&gt;
         &lt;author&gt;&lt;/author&gt;
     &lt;/book&gt;

**The element is not present at all in the returned markup**:

     &lt;book&gt;
         &lt;title&gt;Beowulf&lt;/title&gt;
     &lt;/book&gt;

**The element has a `&lt;null/&gt;` child element** (from [TStamper][1] below):

     &lt;book&gt;
         &lt;title&gt;Beowulf&lt;/title&gt;
         &lt;author&gt;&lt;null/&gt;&lt;/author&gt;
     &lt;/book&gt;

Is there a correct, or canonical way to represent such a `null` value? Are there additional ways than the above examples?

The XML for the examples above is contrived, so don&#39;t read too far into it. :)


  [1]: https://stackoverflow.com/questions/774192/what-is-the-correct-way-to-represent-null-xml-elements/774229#774229

Content Type	Original Author	Original Content on Stackoverflow
Question	dtc	View Question on Stackoverflow
Solution 1 - Xml	Ray Lu	View Answer on Stackoverflow
Solution 2 - Xml	Torsten Marek	View Answer on Stackoverflow
Solution 3 - Xml	Lasse V. Karlsen	View Answer on Stackoverflow

What does i:nil="true" mean?

Xml Problem Overview

Xml Solutions

Solution 1 - Xml

Solution 2 - Xml

Solution 3 - Xml

'Shadows' vs. 'Overrides' in VB.NET

How do you define a good or bad API?

Attributions