If your UML modeling tool has support for specifying an Enumeration, you should use that. It will likely be easier to do and it will give your model stronger semantics.  Visually the result will be very similar to a Class with an `&lt;&lt;enumeration&gt;&gt;` Stereotype, but in the UML metamodel, an Enumeration is actually a separate (meta)type.

    +---------------------+
    |   &lt;&lt;enumeration&gt;&gt;   |
    |    DayOfTheWeek     |
    |_____________________|
    | Sunday              |
    | Monday              |
    | Tuesday             |
    | ...                 |
    +---------------------+

Once it is defined, you can use it as the type of an Attribute just like you would a Datatype or the name one of your own Classes.

    +---------------------+
    |        Event        |
    |_____________________|
    | day : DayOfTheWeek  |
    | ...                 |
    +---------------------+

If you&#39;re using ArgoEclipse or ArgoUML, there&#39;s a pulldown menu on the toolbar which selects among Datatype, Enumeration, Signal, etc that will allow you to create your own Enumerations.  The compartment that normally contains Attributes can then be populated with EnumerationLiterals for the values of your enumeration.

Here&#39;s a picture of a slightly different example in ArgoUML:
![enter image description here][1]


  [1]: http://i.stack.imgur.com/IsPOy.png

Typically you model the enum itself as a class with the `enum` stereotype

Is there a C# equivalent of Python&#39;s `enumerate()` and Ruby&#39;s `each_with_index`?


foreach with index

I am wondering if there is away (possibly a better way) to order by the order of the values in an IN() clause.

The problem is that I have 2 queries, one that gets all of the IDs and the second that retrieves all the information. The first creates the order of the IDs which I want the second to order by. The IDs are put in an IN() clause in the correct order.

So it&#39;d be something like (extremely simplified):

    SELECT id FROM table1 WHERE ... ORDER BY display_order, name

    SELECT name, description, ... WHERE id IN ([id&#39;s from first])

The issue is that the second query does not return the results in the same order that the IDs are put into the IN() clause.

One solution I have found is to put all of the IDs into a temp table with an auto incrementing field which is then joined into the second query.

Is there a better option?

**Note:** As the first query is run &quot;by the user&quot; and the second is run in a background process, there is no way to combine the 2 into 1 query using sub queries.

I am using MySQL, but I&#39;m thinking it might be useful to have it noted what options there are for other DBs as well.

Ordering by the order of values in a SQL IN() clause

I am modeling a class diagram. An attribute of a class is an enumeration. How do I model this? Normally you do something like this:

    - name : string
But how does one do this with an enum?

UML class diagram enum

I am modeling a class diagram. An attribute of a class is an enumeration. How do I model this? Normally you do something like this:
<pre><code class="hljs language-c">- name : string
</code></pre>
But how does one do this with an enum?

The Java documentation says: 

&gt; It is not possible for two invocations of synchronized methods on the
&gt; same object to interleave.

What does this mean for a static method?  Since a static method has no associated object, will the synchronized keyword lock on the class, instead of the object?


Java synchronized static methods: lock on object or class

I have the need to take a string argument and create an object of the class named in that string in Python.  In Java, I would use `Class.forName().newInstance()`.  Is there an equivalent in Python?


----------
Thanks for the responses.  To answer those who want to know what I&#39;m doing: I want to use a command line argument as the class name, and instantiate it.  I&#39;m actually programming in Jython and instantiating Java classes, hence the Java-ness of the question.  `getattr()` works great.  Thanks much.

Does python have an equivalent to Java Class.forName()?

There&#39;s a good discussion of Generics and what they really do behind the scenes over at [this question](https://stackoverflow.com/questions/31693/differences-in-generics), so we all know that `Vector&lt;int[]&gt;` is a vector of integer arrays, and `HashTable&lt;String, Person&gt;` is a table of whose keys are strings and values `Person`s. 
However, what stumps me is the usage of `Class&lt;&gt;`.

The java class `Class` is supposed to also take a template name, (or so I&#39;m being told by the yellow underline in eclipse).  I don&#39;t understand what I should put in there.  The whole point of the `Class` object is when you don&#39;t fully have the information about an object, for reflection and such.  Why does it make me specify which class the `Class` object will hold?  I clearly don&#39;t know, or I wouldn&#39;t be using the `Class` object, I would use the specific one.

How to use Class&lt;T&gt; in Java?

What makes a type different from class and vice versa?

(In the general language-agnostic sense)

What is the difference between Type and Class?

How does one go about and try to find all subclasses of a given class (or all implementors of a given interface) in Java?
As of now, I have a method to do this, but I find it quite inefficient (to say the least).
The method is: 

1. Get a list of all class names that exist on the class path
1. Load each class and test to see if it is a subclass or implementor of the desired class or interface

In Eclipse, there is a nice feature called the Type Hierarchy that manages to show this quite efficiently.
How does one go about and do it programmatically?

How do you find all subclasses of a given class in Java?

I have the following enumeration:

    public enum AuthenticationMethod
	{
		FORMS = 1,
		WINDOWSAUTHENTICATION = 2,
		SINGLESIGNON = 3
	}

The problem however is that I need the word &quot;FORMS&quot; when I ask for AuthenticationMethod.FORMS and not the id 1.

I have found the following solution for this problem ([link][1]):

First I need to create a custom attribute called &quot;StringValue&quot;:

    public class StringValue : System.Attribute
	{
		private readonly string _value;

		public StringValue(string value)
		{
			_value = value;
		}

		public string Value
		{
			get { return _value; }
		}

	}

Then I can add this attribute to my enumerator:

    public enum AuthenticationMethod
	{
		[StringValue(&quot;FORMS&quot;)]
		FORMS = 1,
		[StringValue(&quot;WINDOWS&quot;)]
		WINDOWSAUTHENTICATION = 2,
		[StringValue(&quot;SSO&quot;)]
		SINGLESIGNON = 3
	}

And of course I need something to retrieve that StringValue:

    public static class StringEnum
	{
		public static string GetStringValue(Enum value)
		{
			string output = null;
			Type type = value.GetType();

			//Check first in our cached results...

			//Look for our &#39;StringValueAttribute&#39; 

			//in the field&#39;s custom attributes

			FieldInfo fi = type.GetField(value.ToString());
			StringValue[] attrs =
			   fi.GetCustomAttributes(typeof(StringValue),
									   false) as StringValue[];
			if (attrs.Length &gt; 0)
			{
				output = attrs[0].Value;
			}

			return output;
		}
	}

Good now I&#39;ve got the tools to get a string value for an enumerator.
I can then use it like this:

    string valueOfAuthenticationMethod = StringEnum.GetStringValue(AuthenticationMethod.FORMS);

Okay now all of these work like a charm but I find it a whole lot of work. I was wondering if there is a better solution for this.

I also tried something with a dictionary and static properties but that wasn&#39;t better either.




  [1]: http://www.codeproject.com/Articles/11130/String-Enumerations-in-C

String representation of an Enum

Why can&#39;t enum&#39;s constructor access static fields and methods? This is perfectly valid with a class, but is not allowed with an enum.

What I&#39;m trying to do is store my enum instances in a static Map. Consider this example code which allows lookup by abbreivation:

    public enum Day {
        Sunday(&quot;Sun&quot;), Monday(&quot;Mon&quot;), Tuesday(&quot;Tue&quot;), Wednesday(&quot;Wed&quot;), Thursday(&quot;Thu&quot;), Friday(&quot;Fri&quot;), Saturday(&quot;Sat&quot;);
    
        private final String abbreviation;
    
        private static final Map&lt;String, Day&gt; ABBREV_MAP = new HashMap&lt;String, Day&gt;();
    
        private Day(String abbreviation) {
            this.abbreviation = abbreviation;
            ABBREV_MAP.put(abbreviation, this);  // Not valid
        }
    
        public String getAbbreviation() {
            return abbreviation;
        }
    
        public static Day getByAbbreviation(String abbreviation) {
            return ABBREV_MAP.get(abbreviation);
        }
    }

This will not work as enum doesn&#39;t allow static references in its constructor. It however works just find if implemented as a class:

    public static final Day SUNDAY = new Day(&quot;Sunday&quot;, &quot;Sun&quot;);
    private Day(String name, String abbreviation) {
        this.name = name;
        this.abbreviation = abbreviation;
        ABBREV_MAP.put(abbreviation, this);  // Valid
    }




Why can&#39;t enum&#39;s constructor access static fields?

I am writing a web service in Java, and I am **trying to figure out the best way to define error codes and their associated error strings**. I need to have a numerical error code and an error string grouped together. Both the error code and error string will be sent to the client accessing the web service. For example, when a SQLException occurs, I might want to do the following:

    // Example: errorCode = 1, 
    //          errorString = &quot;There was a problem accessing the database.&quot;
    throw new SomeWebServiceException(errorCode, errorString);

The client program might be shown the message:

&gt; &quot;Error #1 has occured: There was a
&gt; problem accessing the database.&quot;

My first thought was to used an `Enum` of the error codes and override the `toString` methods to return the error strings. Here is what I came up with:

    public enum Errors {
      DATABASE {
        @Override
        public String toString() {
          return &quot;A database error has occured.&quot;;
        }
      },
    
      DUPLICATE_USER {
        @Override
        public String toString() {
          return &quot;This user already exists.&quot;;
        }
      },
    
      // more errors follow
    }

**My question is:** Is there a better way to do this? I would prefer an solution in code, rather than reading from an external file. I am using Javadoc for this project, and being able to document the error codes in-line and have them automatically update in the documentation would be helpful.

Best way to define error codes/strings in Java?

I&#39;ve been programming in Java for a while and just got thrown onto a project that&#39;s written entirely in C#.  I&#39;m trying to come up to speed in C#, and noticed enums used in several places in my new project, but at first glance, C#&#39;s enums seem to be more simplistic than the Java 1.5+ implementation.  Can anyone enumerate the differences between C# and Java enums, and how to overcome the differences?  (I don&#39;t want to start a language flame war, I just want to know how to do some things in C# that I used to do in Java).  For example, could someone post a C# counterpart to Sun&#39;s famous Planet enum example?

    public enum Planet {
      MERCURY (3.303e+23, 2.4397e6),
      VENUS   (4.869e+24, 6.0518e6),
      EARTH   (5.976e+24, 6.37814e6),
      MARS    (6.421e+23, 3.3972e6),
      JUPITER (1.9e+27,   7.1492e7),
      SATURN  (5.688e+26, 6.0268e7),
      URANUS  (8.686e+25, 2.5559e7),
      NEPTUNE (1.024e+26, 2.4746e7),
      PLUTO   (1.27e+22,  1.137e6);

      private final double mass;   // in kilograms
      private final double radius; // in meters
      Planet(double mass, double radius) {
          this.mass = mass;
          this.radius = radius;
      }
      public double mass()   { return mass; }
      public double radius() { return radius; }

      // universal gravitational constant  (m3 kg-1 s-2)
      public static final double G = 6.67300E-11;

      public double surfaceGravity() {
          return G * mass / (radius * radius);
      }
      public double surfaceWeight(double otherMass) {
          return otherMass * surfaceGravity();
      }
    }

    // Example usage (slight modification of Sun&#39;s example):
    public static void main(String[] args) {
        Planet pEarth = Planet.EARTH;
        double earthRadius = pEarth.radius(); // Just threw it in to show usage

        // Argument passed in is earth Weight.  Calculate weight on each planet:
        double earthWeight = Double.parseDouble(args[0]);
        double mass = earthWeight/pEarth.surfaceGravity();
        for (Planet p : Planet.values())
           System.out.printf(&quot;Your weight on %s is %f%n&quot;,
                             p, p.surfaceWeight(mass));
    }

    // Example output:
    $ java Planet 175
    Your weight on MERCURY is 66.107583
    Your weight on VENUS is 158.374842
    [etc ...]

C# vs Java Enum (for those new to C#)

Does Perl have an enumeration type *that adheres to best practices*, or maybe more importantly, does it need one?

The project I am working one uses strings all over the place to denote things that would typically use an Enum in a language like C#.  For example, we have a set of phone numbers in an array of hashes, each associated with a phone type (&quot;Home&quot;, &quot;Work&quot;, &quot;Mobile&quot;, etc.):

    $phone_number-&gt;{type} = &#39;Home&#39;;

Would it be sufficient to use a read-only set of variables here or should an Enum be used?  I&#39;ve found an [`enum` module on CPAN][enum] but it appears to use bare words which violates one of the [Perl Best Practices][PBP].  My thinking on using [read-only variables][Readonly] goes something like this:

    use Readonly;
    
    Readonly my $HOME   =&gt; &#39;Home&#39;;
    Readonly my $WORK   =&gt; &#39;Work&#39;;
    Readonly my $MOBILE =&gt; &#39;Mobile&#39;;
    
    $phone_number-&gt;{type} = $HOME;

Is this a good approach or is there a better way?

[enum]:     http://search.cpan.org/perldoc/enum
[PBP]:      http://oreilly.com/catalog/9780596001735/
[Readonly]: http://search.cpan.org/perldoc/Readonly

Does Perl have an enumeration type?

I was reading Algorithms in a Nutshell (O&#39;Reilly) and came across this symbol in a class diagram.  My guess is that it means the member is protected, but I wanted to see if anyone knows for sure what it means.

What does the &#39;#&#39; symbol mean in a UML class diagram?

I&#39;m creating a sequence diagram, and one of the classes is being observed by another class.  The observed class is calling update in the observer every 5 seconds in a loop.  I need to show this in the sequence diagram.  Is there a way to show it looping indefinitely out of sequence as it were?

Or does it not make sense in the context of a sequence diagram; should I not include it? Or should I include it in a different type of diagram?

How to represent a call being made in a loop in a sequence diagram?

I&#39;m now using NetBeans as my IDE-of-choice, and it has a plugin for UML modeling. In the class diagram, there are model elements known as `Boundary Class`, `Control Class`, and `Entity Class`. However, I can&#39;t find a good definition of them, but I did find [this site][1] on UML Class Diagrams.


  [1]: http://www.developer.com/design/article.php/10925_2206791_2

In UML class diagrams, what are Boundary Classes, Control Classes, and Entity Classes?

I&#39;ve had a hard time understanding the difference between composition and aggregation in UML. Can someone please offer me a good compare and contrast between them? I&#39;d also love to learn to recognize the difference between them in code and/or to see a short software/code example.

Edit: Part of the reason why I ask is because of a reverse documentation activity that we&#39;re doing at work. We have written the code, but we need to go back and create class diagrams for the code. We&#39;d just like to capture the associations properly.

Aggregation versus Composition

On a UML diagram, what is the correct way to represent a template class?

What is the correct way to represent template classes with UML?

What are the easy algorithms to implement Voronoi diagram? 

I couldn&#39;t find any algorithm specially in pseudo form. Please share some links of Voronoi diagram algorithm, tutorial etc.

Easiest algorithm of Voronoi diagram to implement?

Please suggest tools for creating Class Diagrams with the following criteria:

 - It should be platform-independent because I use Linux and the file is expected to be edited by other members of the team using Windows/Mac
 - Free, because there no such free tool, we should create one
 - It would also be nice if you can include a screenshot of the class diagram produced, just to make sure that the tool is actually used for creating Class Diagrams and not just any other types of diagrams

Also, please only suggest the tools that you&#39;ve actually used.

UPDATE: Please DO NOT include those UML Diagram tools that cannot create Class Diagrams.


Tools for creating Class Diagrams

In a flowchart or process diagram, what is the symbol for a FIFO queue?

What is the symbol for a queue?

This question came up today and I couldn&#39;t find any historical answer as to why a database is always represented as a cylinder.  I am hoping someone in the stack world would know why and ***have a link or something backing it up***.

Content Type	Original Author	Original Content on Stackoverflow
Question	Martijn	View Question on Stackoverflow
Solution 1 - Class	James B	View Answer on Stackoverflow
Solution 2 - Class	Tom Morris	View Answer on Stackoverflow
Solution 3 - Class	annakata	View Answer on Stackoverflow

UML class diagram enum

Class Problem Overview

Class Solutions

Solution 1 - Class

Solution 2 - Class

Solution 3 - Class

Ordering by the order of values in a SQL IN() clause

foreach with index

Attributions