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<div align="right">&nbsp; <font face="Times New Roman, Times, serif" size="2">&copy; 
  Copyright <a href="http://www.azzurri.jp">Azzurri Ltd.</a> 2003, 2004. All rights 
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      <td align=LEFT valign=TOP colspan="2" bgcolor="#0080C0"><b><font face="Arial,Helvetica"><font color="#FFFFFF">&nbsp;Eclipse 
        Corner Article</font></font></b></td>
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  <h1><img src="images/Idea.jpg" align=CENTER width="120" height="86" /></h1>
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<h1 align="center">JET Tutorial Part 2 (Write Code that Writes Code)</h1>

<blockquote>
<b>Summary</b>

<br/>
<p>In Part 2 of this JET (Java Emitter Templates) tutorial, we will take a look 
  at the JET engine API. You will learn how to write plug-ins that use the classes 
  in the JET package to generate Java source code.</p>
  <p>As a real-world example, we will create a plug-in that takes user input and 
    generates a Typesafe Enumeration class. The generated source code is based 
    on a JET template that can be distributed with the plug-in, allowing users 
    of the plug-in to customize the generated code by editing the template.</p>
<p>This article also provides a short reference to the JET API.</p>
  <p>Contributed by Remko Popma, Azzurri Ltd., remko.popma at azzurri dot jp, 
    August 26, 2003. Last update: May 31, 2004 for EMF 2.0 (Eclipse 3.0).</p>

</blockquote>

<hr width="100%"/>

<h2>Source Code </h2>
<p>To run the example or view the source for code for this article you can unzip 
  <a href="org.eclipse.emf.examples.jet.article2_2.0.0.zip">org.eclipse.emf.examples.jet.article2_2.0.0.zip</a> 
  into your <i>plugins/</i> subdirectory. To use the example plug-in, you will 
  need <a href="http://www.eclipse.org/emf/" target="_blank">EMF</a> plug-in version 
  2.0 installed.</p>

<h2>Introduction </h2>
<center>
  <table border="1" cellspacing="0" width="80%" cellpadding="3">
    <tbody> 
    <tr> 
    <td> 
      <p><b>Translation vs. Generation</b></p>
        <p>An aspect of JET templates that is at first confusing is that generating 
          text takes two steps: translation and generation. The first step is 
          translating the template to a template implementation class. The second 
          step is using this template implementation class to generate the text. 
        </p>
      <p>If your goal with JET is to generate Java source code, it can be confusing 
        that the template translation step also results in Java source code. Remember 
        that this source code is <i>not</i> the generated text. The source code 
        that is the result of the translation step is simply another form of the 
        template. </p>

        <p>If you have used JSP and servlets before, you can think of a JET template 
          as being equivalent to a JSP page. A JET template is translated to a 
          template implementation class, just like a JSP page is translated to 
          a servlet. The second step, where the template implementation class 
          generates text, is equivalent to the servlet creating and returning 
          HTML.</p>
    </td>
  </tr>
  </tbody> 
</table>
</center>
  
<p><a href="../Article-JET/jet_tutorial1.html">Part 1</a> of this tutorial introduced 
  JET templates and explained how you can convert a project to a JET project to 
  have the JET Builder automatically translate templates in your project to template 
  implementation classes. </p>
<p>In part 2 of this tutorial, we will focus on writing a plug-in that uses the 
  classes in the JET package to generate Java source code. A plug-in that generates 
  text from a JET template can no longer rely on the JET Nature and JET Builder 
  to automatically translate templates. This is because JET Nature and JET Builder 
  operate only on workspace projects, not on plug-ins. Plug-ins need to use the 
  classes in the JET package to translate their templates. </p>

<p>The next section will discuss some of the classes in the <tt class="code">org.eclipse.emf.codegen</tt> 
  package. We will see what the steps are to generate source code with JET, and 
  how the JET engine classes fit in. If you are anxious to see some code that 
  shows how to use these classes in practice, you can go straight to <a href="#example_plugin">A 
  Plug-in that Generates Source Code</a>. </p>

<h2>Some JET Classes</h2>
<p>In this section, we will take a closer look at some of the classes in the JET 
  package. They can roughly be divided into two groups: </p>
<ul>
  <li>Lower-level classes dealing with the nuts and bolts of translating a template 
    to a template implementation class. The <tt class="code">JETCompiler</tt> class brings 
    all these lower-level classes together to provide a single API for template 
    translation. </li>

  <li>Higher-level classes that build on top of <tt class="code">JETCompiler</tt> to accomplish 
    user tasks. In Part 1 of this tutorial, we have already seen <tt class="code">JETNature</tt> 
    and <tt class="code">JETBuilder</tt> at work. Other high-level classes are <tt class="code">CodeGen</tt> 
    and <tt class="code">JETEmitter</tt>. </li>

</ul>
<p>The lower-level classes are not discussed in-depth in this article. For a description 
  of all classes in the <tt class="code">org.eclipse.emf.codegen</tt> plug-in, see the <a href="#jet_api_overview">JET 
  API Overview</a> section below. In the rest of this section, we will focus on 
  a few of the higher-level classes.</p>
<h4><tt class="code">org.eclipse.emf.codegen.jet.JETCompiler</tt></h4>
<p><tt class="code">JETCompiler</tt> is the core class for template translation. This class 
  is responsible for translating templates to the Java source code of a template 
  implementation class. The actual translation is delegated to other classes in 
  the same package. Clients create a JETCompiler object for a particular template 
  and then call the <tt class="code">parse</tt> method followed by the <tt class="code">generate</tt> 
  method to write the Java source code for the resulting template implementation 
  class to a specified stream.</p>

<h4><tt class="code">org.eclipse.emf.codegen.jet.JETEmitter</tt></h4>
<p><tt class="code">JETEmitter</tt> provides a convenient high-level API for users of the 
  JET package. The <tt class="code">generate</tt> method of this class combines template 
  translation and text generation into a single step. By taking care of the gory 
  details of translating templates and compiling the Java source code of the translated 
  template implementation class, JETEmitter lets you focus on the final generator 
  output.</p>
<p>Another way of looking at JETEmitter is that it abstracts away the translation 
  step and lets you pretend that you can directly generate text with a template. 
  Following the <a href="http://www.joelonsoftware.com/articles/LeakyAbstractions.html" target="_blank">Law 
  of Leaky Abstractions</a>, we cannot always get away with this, and the <a href="#jetemitter_gotchas">JETEmitter 
  Gotchas</a> section below points to a few places where you have to be careful.</p>
<p>JETEmitter is the class we will be using in our plug-in, so we will go into 
  a little more detail here.</p>

<p>A JETEmitter object is constructed with the uri of the template used to generate 
  text. Any type of uri is acceptable as long as a protocol handler is available. 
  This means that <tt class="code">file:/</tt> uris, <tt class="code">ftp:/</tt> uris and <tt class="code">http:/</tt><i> 
  </i>uris can all be used. Eclipse adds special protocol handlers for <tt class="code">platform:/base</tt>/, 
  <tt class="code">platform:/plugin/</tt>, <tt class="code">platform:/fragment/</tt> and <tt class="code">platform:/resource/</tt> 
  uris, so plug-ins can use a uri like <tt class="code">platform:/resource/myproject/myfolder/mytemplate.jet</tt> 
  to specify a template file.  Note: Eclipse 3.0 has introduced <tt class="code">bundleentry</tt> to its list
  of special protocols.  It should be used in references to Eclipse elements such as plugins and features.</p>

<p>In our example plug-in, we will distribute our template file together with our 
  plug-in, so the template file will be located in a <i>myplugin/templates/</i> 
  folder under the Eclipse <i>plugins/</i> folder. The following code can then 
  be used to locate and generate a template from this folder:</p>
<pre class="code"> String pluginId = "myplugin.id";
 String base = Platform.getBundle(pluginId).getEntry("/").toString();
 String uri = base + "templates/myTemplate.javajet";
 JETEmitter emitter = new JETEmitter(uri);
 String generatedText = emitter.generate(new Object[] {parameter});</pre>
<p>After constructing a JETEmitter object, clients then call <tt class="code">generate</tt> 
  on it to generate text. The <tt class="code">generate</tt> method will perform the following 
  steps:</p>

<ol>
  <li>Create a project called <i>.JETEmitters</i> in the workspace </li>
  <li>Prepare this project by giving it the Java Nature and adding classpath variables 
    to its classpath </li>
  <li>Translate the template to a template implementation Java source file in 
    the <i>.JETEmitters</i> project </li>
  <li>Build the project to compile the template implementation source code to 
    a Java <i>.class</i> file </li>
  <li>Call the <tt class="code">generate</tt> method on the translated Java template implementation 
    class and return the generated text as a String</li>
</ol>
<p>* <i>.JETEmitters</i> is the default name for the project that is created during the template
translation.  This value can be changed by the <tt class="code">setProjectName</tt> method.</p>


<p>Our example plug-in will use JETEmitter and save the generated text to a Java 
  source file in the workspace. The figure below shows the steps for generating 
  source code using JETEmitter. </p>
<p><img alt="Using JETEmitter to generate text from a plugin" src="images/jetemitter.gif"/> </p>
<h3><a name="jetemitter_gotchas"></a>JETEmitter Gotchas</h3>
<p>The JETEmitter class combines template translation and text generation into 
  a single step, which makes it a very convenient tool. However, it is important 
  that you know what takes place under the hood, otherwise you might be in for 
  some nasty surprises. This section highlights some &quot;gotchas&quot; that 
  I ran into, so that you don't make the same mistakes.</p>

<h4>1. Plug-in Initialization Required </h4>
<p>It is not easy to use JET outside of Eclipse. JET is designed to run only as 
  a workspace application. Any application using JET must minimally run as an 
  Eclipse &quot;headless&quot; application so that plug-in initialization takes 
  place. (The term headless refers to running Eclipse without the user interface.)</p>
<p>This means that using JETEmitter from a simple standalone application (a standard 
  Java class with a <tt class="code">main</tt> method) <i>will not work</i>:</p>
<pre class="code"> // This fails: cannot use JETEmitter from a standalone application
 public static void main(String[] args) {
     JETEmitter emitter = new JETEmitter("/myproject/templates/HelloWorld.txtjet");
 
     // this will throw a NullPointerException
     String result = emitter.generate(new NullProgressMonitor(), {"hi" });
 
     System.out.println(result);
</pre>

<p>Note that this is not a restriction of just the JETEmitter class, many of the 
  classes in the <tt class="code">org.eclipse.emf.codegen</tt> plug-in have dependencies 
  on other plug-ins. The <a href="#appendix">Appendix</a> section below has more 
  details on using JET from standalone applications.</p>
<p>In the rest of this article we will assume that our code is running from inside 
  a plug-in.</p>
<h4>2. Classloader Issues </h4>
<p>You may get a NoClassDefFoundError when you pass a custom object as the argument 
  to the <tt class="code">JETEmitter.generate</tt> method. This can happen if the object 
  you pass as the argument is not one of the java "bootstrap" classes (the bootstrap 
  classes are the runtime classes in rt.jar and internationalization classes in 
  i18n.jar).</p>

<p>To prevent this error you must specify the classloader of your plug-in when 
  using JETEmitter. If no classloader is specified, JETEmitter uses the classloader 
  of its own class, which is usually the classloader for the <tt class="code">org.eclipse.emf.codegen</tt> 
  plug-in, and this classloader can't see much. In recent versions of EMF (since 
  version 1.1.0 build 20030527_0913VL), JETEmitter has a constructor that takes 
  a classloader argument.</p>
<p>Note that another way to specify a classloader is to subclass JETEmitter in 
  your own project; if no classloader is specified, JETEmitter will use the classloader 
  of this subclass. (If you are using an older version of EMF, there are no constructors 
  that take a classloader argument and you will have no choice but to subclass 
  JETEmitter in your own project.)</p>
<p>The example below shows an action class that translates and invokes a selected 
  template using JETEmitter. The example shows how a JETEmitter can be constructed 
  <img src="images/tag_1.gif" width="24" height="13"/>with a classloader parameter or by <img src="images/tag_2.gif" width="24" height="13"/>constructing 
  an anonymous subclass.</p>
<pre class="code">package org.eclipse.emf.examples.jet.article2.actionexample;
// imports omitted
public class EmitAction implements IActionDelegate {
    protected ISelection selection;
 
    public void selectionChanged(IAction action, ISelection selection) {
        this.selection = selection;
        action.setEnabled(true);
    }
 
    public void run(IAction action) {
        List files = (selection instanceof IStructuredSelection)
                ? ((IStructuredSelection) selection).toList()
                : Collections.EMPTY_LIST;
                
        for (Iterator i = files.iterator(); i.hasNext();) {
            IFile file = (IFile) i.next();
            IPath fullPath = file.getFullPath();
 
            String templateURI = "platform:/resource" + fullPath;
            <b>Class</b><b>Loader classloader = getClass().getClassLoader();</b>
<img src="images/tag_1.gif" width="24" height="13"/>         JETEmitter emitter = new JETEmitter(templateURI, <b>classloader</b>);
 
            // <b>or: use an anonymous subclass</b>

<img src="images/tag_2.gif" width="24" height="13"/>         // emitter = <b>new JETEmitter(templateURI) {}</b>; // notice the brackets
            
            try {
                IProgressMonitor monitor = new NullProgressMonitor();
                String[] arguments = new String[] { "hi" };
 
                String result = emitter.generate(monitor, arguments);
                
                saveGenerated(result, file);
 
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }
 
    // saveGenerated method omitted
}
</pre>
<h4>3. Classpath Issues </h4>
<p>JETEmitter translates your templates to Java source files in the <i>.JETEmitters</i> 
  project, and invokes the JavaBuilder to compile these source files. If your 
  templates use classes that are not standard Java classes, or not in the EMF 
  plug-in, you will need to add these classes to the classpath of the <i>.JETEmitters</i> 
  project, or the JavaBuilder cannot compile the template implementation source 
  files.  Fortunately, JETEmitter provides a simple way to do this through the method 
  <tt class="code">addVariable</tt> which adds a <i>Classpath Variable</i> to the <i>.JETEmiter</i> project.</p>
<p>A <i>Classpath Variable</i> is a workspace-wide name that is used in Eclipse to refer to a jar file or
directory.  The list of all such variables can be seen using the Window &gt; Preferences &gt; Java &gt; 
Classpath Variables menua action.. Your program will need to add a classpath variable for each
  jar file or directory that is needed on the classpath of the <i>.JETEmiter</i> project.</p>
  
  
<h2><a name="example_plugin"></a>A Plug-in that Generates Source Code </h2>
<p>In this part of the JET Tutorial, we will write an Eclipse plug-in that uses 
  a JET template to generate Java source code for typesafe enumerations.</p>
<p>Our plug-in has to perform the following tasks:</p>
<ol>
  <li>Collect user input values for the variables in our template: the class name, 
    the type and name of the attributes of the typesafe enumeration class, and 
    the values of these attributes for each instance. We will write a simple GUI 
    to collect these values.</li>
  <li>Translate the JET template file to a Java template implementation class</li>

  <li>Invoke the template implementation class with an object that contains the 
    user input values collected by the GUI</li>
  <li>Save the resulting generated source code to a location obtained from the 
    GUI</li>
</ol>
<p>In the following sections we will go through the steps above one by one.</p>
<h3><a name="typesafe_enum_example"></a>Typesafe Enumerations</h3>
<p>Let's have a look at a typesafe enumeration class to see what kind of source 
  code we want to generate. The Digit class below is an example typesafe enum.</p>
<pre class="code"> // an example typesafe enum
 package x.y.z;
 public class Digit { 
<img src="images/tag_1.gif" width="24" height="13"/>  public static final Digit ZERO = new Digit(0, "zero");
     public static final Digit ONE = new Digit(1, "one");
     public static final Digit TWO = new Digit(2, "two");
     public static final Digit THREE = new Digit(3, "three");
     // ...
     public static final Digit NINE = new Digit(9, "nine");
 
     private static final Digit[] ALL = 
         {ZERO, ONE, TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE};
 

<img src="images/tag_2.gif" width="24" height="13"/>  private final int value;
     private final String name;
 
     private Digit(int value, String name) { 
         this.value = value; 
         this.name = name; 
     }
 
<img src="images/tag_3.gif" width="24" height="13"/>  public static Digit lookup(int key) {
         for (int i = 0; i &lt; ALL.length; i++) {
             if (key == ALL[i].getValue()) { return ALL[i]; }
         }
         // lookup failed:
         // we have no default Digit, so we throw an exception
<img src="images/tag_4.gif" width="24" height="13"/>      throw new IllegalArgumentException("No digit exists for " + key);
     }
 
     public int getValue() { return value; }
     public int getName() { return name; }
     public String toString() { return getName(); }
 }</pre>
<p>Let's take a closer look at this class. First of all, the Digit class has several 
  <b><img src="images/tag_1.gif" width="24" height="13"/>instances</b> - the constants 
  ZERO, ONE, TWO, etc. Each instance is defined by its Java variable name, "ZERO", 
  "ONE", "TWO"..., and the values for each <b><img src="images/tag_2.gif" width="24" height="13"/>attribute</b> 
  of the enumeration class. Most typesafe enums have one or more attributes. The 
  Digit class has two attributes: a <tt class="code">value</tt> integer and a <tt class="code">name</tt> 
  String.</p>

<p>Our example Digit class also has a <b><img src="images/tag_3.gif" width="24" height="13"/><tt class="code">lookup</tt></b> 
  method, which returns the instance whose <tt class="code">value</tt> attribute equals 
  the specified int parameter. A lookup method introduces the concept of <b>key 
  attributes</b>. Many typesafe enums have one or more attributes that uniquely 
  distinguish one instance from another.</p>
<p><i>Note that key attributes are not required: the Java VM guarantees that every 
  newly constructed object is unique, so it is possible to have typesafe enumerations 
  that have no attributes at all, and simply distinguish their instances with 
  the <b>==</b> instance identity operator. This works fine, but often it is convenient 
  to have a key attribute that uniquely identifies an instance, and a <tt class="code">lookup</tt> 
  method that finds an instance for a specified key value.</i></p>

<p>Our template does have a <tt class="code">lookup</tt> method, so we need to decide what 
  to do if <img src="images/tag_4.gif" width="24" height="13"/>no instance is found 
  for the specified key value. Basically there are three options: throwing an 
  Exception, returning a designated &quot;default&quot; instance, or returning 
  <tt class="code">null</tt>. Which option is best depends on the application in which 
  the class is used, so we should probably let the user decide.</p>
<p>Now that we've studied typesafe enums in more detail, let's summarize what 
  is customizable in a typesafe enumeration:</p>
<ul>
  <li>package name </li>
  <li>class name </li>

  <li>attributes, where each attribute </li>
  <ul>
    <li>has a type </li>
    <li>has a name </li>
    <li>may be a key attribute </li>
  </ul>
  <li>instances, where each instance </li>

  <ul>
    <li>has a name </li>
    <li>has a value for every attribute </li>
    <li>may be the default instance to return for failed lookups</li>
  </ul>
</ul>
<h3><a name="typesafe_enum_model"></a>A Simple Typesafe Enumeration Model </h3>
<p>A simple model for the customizable parts of a typesafe enum could look something 
  like this:</p>
<p></p>

<table border="1" cellspacing="0">
  <tbody> 
  <tr> 
    <td><tt class="code">TypesafeEnum</tt></td>
  </tr>
  <tr> 
    <td><tt class="code">getInstances() : Instance[]<br/>
      getAttributes() : Attribute[]<br/>
      getKeyAttributes() : Attribute[]<br/>

      getDefaultInstance() : Instance<br/>
      getPackageName() : String<br/>
      getClassName() : String</tt></td>
  </tr>
  </tbody> 
</table>
<p></p>
<table border="1" cellspacing="0">
  <tbody> 
  <tr> 
    <td><tt class="code">Instance</tt></td>

  </tr>
  <tr> 
    <td><tt class="code"> getName() : String<br/>
      getAttributeValues() : Properties<br/>
      getAttributeValue(Attribute) : String<br/>
      isDefault() : boolean</tt></td>
  </tr>

  </tbody> 
</table>
<p></p>
<table border="1" cellspacing="0">
  <tbody> 
  <tr> 
    <td><tt class="code">Attribute</tt></td>
  </tr>
  <tr> 
    <td><tt class="code"> getName() : String<br/>

      getType() : String<br/>
      isKey() : boolean</tt></td>
  </tr>
  </tbody> 
</table>
<p></p>
<p>In the next section we will use these classes to convert our Digit class to 
  a JET template for typesafe enumerations.</p>
<h3><a name="typesafe_enum_template"></a>A Typesafe Enumeration Template </h3>
<p>Now that we have a model, we can take our Digit class and replace all Digit-specific 
  code with JET scriptlets and expressions that call our model classes. The resulting 
  template could look something like this:</p>

<pre class="code"> <span class="highlight"><span class="highlight">&lt;%@ jet package="translated" imports="java.util.* article2.model.*" class="TypeSafeEnumeration" %&gt;</span></span>
 <span class="highlight"><span class="highlight">&lt;% TypesafeEnum enum = (TypesafeEnum) argument; %&gt;</span></span>
 package <span class="highlight">&lt;%=enum.getPackageName()%&gt;</span>;
 
 /**
  * This final class implements a type-safe enumeration
  * over the valid instances of a <span class="highlight">&lt;%=enum.getClassName()%&gt;</span>.
  * Instances of this class are immutable.
  */
 public final class <span class="highlight">&lt;%=enum.getClassName()%&gt;</span> {
 
 <span class="highlight">&lt;% for (Iterator i = enum.instances(); i.hasNext(); ) { %&gt;</span>

 <span class="highlight">&lt;%     Instance instance = (Instance) i.next(); %&gt;</span>
 
     // <b>instance definition</b>
     public static final <span class="highlight">&lt;%=enum.getClassName()%&gt;</span> <span class="highlight">&lt;%=instance.getName()%&gt;</span> = 
<img src="images/tag_1.gif" width="24" height="13"/>      new <span class="highlight">&lt;%=enum.getClassName()%&gt;</span>(<span class="highlight">&lt;%=instance.constructorValues()%&gt;</span>);
 <span class="highlight">&lt;% } %&gt;</span>

 
 <span class="highlight">&lt;% for (Iterator i = enum.attributes(); i.hasNext(); ) { %&gt;</span>
 <span class="highlight">&lt;%     Attribute attribute = (Attribute) i.next(); %&gt;</span>
 
     // <b>attribute declaration</b>
<img src="images/tag_2.gif" width="24" height="13"/>  private final <span class="highlight">&lt;%=attribute.getType()%&gt;</span> m<span class="highlight">&lt;%=attribute.getCappedName()%&gt;</span>;
 <span class="highlight">&lt;% } %&gt;</span>

 
     /**
      * Private <b>constructor</b>.
      */
<img src="images/tag_3.gif" width="24" height="13"/>  private <span class="highlight">&lt;%=enum.getClassName()%&gt;</span>(<span class="highlight">&lt;%=enum.constructorParameterDescription()%&gt;</span>) {
 <span class="highlight">&lt;% for (Iterator i = enum.attributes(); i.hasNext(); ) { %&gt;</span>
 <span class="highlight">&lt;%     Attribute attribute = (Attribute) i.next(); %&gt;</span>
<img src="images/tag_4.gif" width="24" height="13"/>      m<span class="highlight">&lt;%=attribute.getCappedName()%&gt;</span> = <span class="highlight">&lt;%=attribute.getUncappedName()%&gt;</span>;
 <span class="highlight">&lt;% } %&gt;</span>

     }
               
 // <b>getter accessor methods</b>
 <span class="highlight">&lt;% for (Iterator i = enum.attributes(); i.hasNext(); ) { %&gt;</span>
 <span class="highlight">&lt;%     Attribute attribute = (Attribute) i.next(); %&gt;</span>
     /**
      * Returns the <span class="highlight">&lt;%=attribute.getName()%&gt;</span>.
      *
      * @return the <span class="highlight">&lt;%=attribute.getName()%&gt;</span>. 
      */
     public <span class="highlight">&lt;%=attribute.getType()%&gt;</span> get<span class="highlight">&lt;%=attribute.getCappedName()%&gt;</span>() {
         return m<span class="highlight">&lt;%=attribute.getCappedName()%&gt;</span>;
     }
 
 <span class="highlight">&lt;% } %&gt;</span>     
 
     // lookup method omitted...
 }</pre>

<p>As you can see, the template calls some methods that were not in the simple 
  model we introduced earlier. We have added a few convenience methods, like the 
  <tt class="code"><img src="images/tag_2.gif" width="24" height="13"/>Attribute.getCappedName()</tt> 
  and <tt class="code"><img src="images/tag_4.gif" width="24" height="13"/>getUncappedName()</tt> 
  methods. Such methods help to keep the template simple.</p>
<p>Another example of methods we added to the model are the <tt class="code"><img src="images/tag_3.gif" width="24" height="13"/>TypesafeEnum.constructorParameterDescription()</tt> 
  method and the <tt class="code"><img src="images/tag_1.gif" width="24" height="13"/>Instance.constructorValues()</tt> 
  method. The implementation of the <tt class="code">constructorValues</tt> method is shown 
  below. </p>

<pre class="code">// class Instance
/**
 * Convenience method that returns the attribute values of this instance,
 * in the order expected by the constructor of this instance.
 * 
 * @return a comma-separated list of all attribute values of this instance,
 *         formatted like <tt class="code">attrib1-value, attrib2-value (, ...)</tt>
 */
public String constructorValues() {
    StringBuffer result = new StringBuffer();
    for (Iterator i = getType().attributes(); i.hasNext(); ) {
        Attribute attribute = (Attribute) i.next();
        result.append(getAttributeValue(attribute));
        if (i.hasNext()) {
            result.append(", ");
        }
    }
    return result.toString();
}
</pre>
<p>The <tt class="code">constructorValues</tt> method loops through the attributes of the 
  typesafe enum, looks up the value for each attribute in the instance, and concatenates 
  these values into a string, separated by commas. For example, in our <tt>Digit</tt> 
  typesafe enum class above, this method would return <tt>&quot;0, \&quot;zero\&quot;&quot;</tt> 
  for the &quot;ZERO&quot; instance. </p>

<p>We could have looped through the attribute values in the template, but that 
  would have made the template much more difficult to read. Pushing this logic 
  into the model made the template more readable and easier to maintain. On the 
  other hand, we lost some flexibility because users cannot customize that logic 
  anymore by editing the template. This is a trade-off you have to make. Which 
  is better depends on your template and your application.</p>
<h3><a name="gui"></a>A GUI to Collect User Input </h3>
<p>Now that we have a model and a template, we still need two more pieces to finish 
  our plug-in: we need a GUI to collect values from the user to populate our model 
  with, and we need to invoke our template with the populated model to generate 
  source code and save this source code to a location in the workspace.</p>
<p>Let's start with the GUI. The workbench provides a few wizards that do something 
  similar to what we have in mind, for example the New Class, New Interface and 
  New JUnit TestCase wizards. It probably makes sense to have our GUI look similar 
  to these wizards and make it accessible from the standard menu and toolbar locations.</p>
<p>Our wizard has three pages. The first page, shown below, looks like a simplified 
  version of the New Class wizard. In fact, we are using the same framework that 
  the New Class wizard uses, the <tt class="code">org.eclipse.jdt.ui.wizards</tt> package. 
  In the first page, we collect the package name and the class name of the typesafe 
  enum, and the location where the result should be saved.</p>
<p><img alt="GUI wizard page one: class, package and location of the typesafe enum" src="images/enum_gui_page1.gif"/> 
</p>
<p></p>
<p>Our second page collects information on the attributes of the typesafe enum 
  class. Every attribute has a name and a type, and may be one of the key attributes. 
  Our second wizard page is shown below:</p>

<p><img alt="GUI wizard page two: attributes of the typesafe enum" src="images/enum_gui_page2.gif"/></p>
<p></p>
<p>Our third and last wizard page, shown below, collects information on the instances 
  of the typesafe enum. The user inputs the instance name, and for each instance 
  provides values for all attributes.</p>
<p>Finally, one of the instances may be the &quot;default&quot; instance, which 
  is the instance returned by the <tt class="code">lookup</tt> method if no instance was 
  found for the specified key attribute values.</p>
<p><img alt="GUI wizard page three: instances of the typesafe enum" src="images/enum_gui_page3.gif"/></p>
<h3><a name="invoke_plugin_template"></a>Invoking the Template </h3>
<p>Now that we have a GUI to populate our model, we can finally use what we learned 
  in the first part of this article, and generate source code with our template.</p>

<p>When a user presses Finish on the wizard, the <tt class="code">performFinish</tt> method 
  in our wizard is called. The code below shows how we <img src="images/tag_1.gif" width="24" height="13"/>use 
  a custom subclass of JETEmitter to <img src="images/tag_2.gif" width="24" height="13"/>add 
  the jar file of our plug-in to the classpath of the <i>.JETEmitters</i> project 
  before we <img src="images/tag_3.gif" width="24" height="13"/>call generate on 
  the JETEmitter. The generated typesafe enum source code is <img src="images/tag_4.gif" width="24" height="13"/>saved 
  to the location in the workspace that the user specified.</p>
<pre class="code"> // class NewTypesafeEnumCreationWizard
 protected void finishPage(IProgressMonitor monitor) 
 throws InterruptedException, CoreException {
 
     String pluginId = "org.eclipse.emf.examples.jet.article2";
     String base = Platform.getBundle(pluginId).getEntry("/").toString();
     String relativeUri = "templates/TypeSafeEnumeration.javajet";
<img src="images/tag_1.gif" width="24" height="13"/>  JETEmitter emitter = new JETEmitter(base + relativeUri, getClass().getClassLoader());
<img src="images/tag_2.gif" width="24" height="13"/>  emitter.addClasspathVariable("JET_TUTORIAL", pluginId);
 
     TypesafeEnum model = mPage1.getTypesafeEnumModel();
     IProgressMonitor sub = new SubProgressMonitor(monitor, 1);

<img src="images/tag_3.gif" width="24" height="13"/>  String result = emitter.generate(sub, new Object[] { model });
     monitor.worked(1);
 
<img src="images/tag_4.gif" width="24" height="13"/>  IFile file = save(monitor, result.getBytes());
 
     selectAndReveal(file);
     openResource(file);
 }</pre>
<h3><a name="pluginxml"></a>Registering our Wizard </h3>
<p>Our final code snippet below shows the part of our <tt class="code">plugin.xml</tt> configuration 
  file where we register our wizard as a contribution to the workbench.</p>
<pre class="code">   &lt;extension point="org.eclipse.ui.newWizards"&gt;
      &lt;wizard 
            name="Typesafe Enum"
            icon="icons/newenum_wiz.gif"
            category="org.eclipse.jdt.ui.java"
            id="org.eclipse.emf.examples.jet.article2.ui.NewTypesafeEnumCreationWizard"&gt;
         &lt;description&gt;
            Create a Typesafe Enumeration
         &lt;/description&gt;
         &lt;class class="org.eclipse.emf.examples.jet.article2.ui.NewTypesafeEnumCreationWizard"&gt;
<img src="images/tag_1.gif" width="24" height="13"/>         &lt;parameter name="javatype" value="true"/&gt;
         &lt;/class&gt;
      &lt;/wizard&gt;
   &lt;/extension&gt;
</pre>
<p>Now our wizard is activated when users select File &gt; New &gt; Other &gt; 
  Java &gt; Typesafe Enum from the workbench, as shown in the image below. </p>
<p><img alt="Typesafe Enum wizard shows up in the New creation wizard" src="images/new_creation_wizard.gif"/> 
</p>
<p>Note that we set the <tt class="code"><img src="images/tag_1.gif" width="24" height="13"/>javatype</tt> 
  attribute to true in the wizard extension element in the <tt class="code">plugin.xml</tt> 
  file. This will cause our wizard to show up as an action on the toolbar in the 
  Java Perspective, as shown in the image below.</p>

<p><img alt="Typesafe Enum wizard shows up as an action on the toolbar in the Java Perspective" src="images/new_toolbar.gif"/> 
</p>
<p></p>
<h2><a name="conclusion"></a>Conclusion </h2>
JET can be a great help for applications that need to generate text. Templates 
are as much of an improvement to code generation as JSP pages were to old style 
servlets. 
<p>When using JET, you need to decide whether you want to distribute your templates 
  with your application, or distribute only the template implementation classes.</p>
<p>If your goal is to simplify the text generation capabilities of your application, 
  then using JET Nature and JET Builder to automatically translate your templates 
  is a good choice. See <a href="../Article-JET/jet_tutorial1.html">JET Tutorial 
  Part 1</a> for details. In that case you only need to distribute the translated 
  template implementation classes with your application, not the templates themselves.</p>
<p>On the other hand, if it is important for your application that users have 
  ultimate control over the generated text, you may want to distribute the template 
  files themselves with your application. In that case, you will need to translate 
  these templates every time you generate text. The plug-in we wrote in this article 
  is an example of this type of application.</p>
<p>This article explained what classes are available in the JET package to achieve 
  this and showed how to use these classes with an Eclipse plug-in. The appendix 
  below provides an overview of the JET API and shows how it can be used in headless 
  or standalone applications.</p>

<h2><a name="appendix"></a>Appendix</h2>
<h3><a name="jet_api_overview"></a>JET API Overview </h3>
<b>Package org.eclipse.emf.codegen</b> 
<p></p>
<table border="1" cellspacing="0">
  <tbody> 
  <tr> 
    <td><b>Class</b></td>
    <td><b>Description</b></td>
  </tr>

  <tr> 
    <td valign="top"><tt class="code">CodeGen</tt></td>
    <td> 
      <p>The <tt class="code">CodeGen</tt> class can translate a JET template to Java source 
        code and optionally merge the template implementation Java source code 
        with an existing Java class. <tt class="code">CodeGen</tt> can be used as an Eclipse 
        headless application. The <tt class="code">run</tt> method expects a String array parameter 
        of two or three elements: </p>

      <ul>
        <li> the uri of the template to translate </li>
        <li>the target path where the translation result should be saved </li>
        <li>an optional <tt class="code">JMerge</tt> control model file specifying how to merge 
          the new translation result with the source code of an existing Java 
          class</li>
      </ul>

    </td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">CodeGenPlugin</tt></td>
    <td>The plug-in class for the JET package.</td>
  </tr>
  </tbody>
</table>
<p></p>

<b>Package org.eclipse.emf.codegen.jet</b> 
<p></p>
<table border="1" cellspacing="0">
  <tbody> 
  <tr> 
    <td><b>Class</b></td>
    <td><b>Description</b></td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">IJETNature</tt></td>

    <td>Interface extending <tt class="code">org.eclipse.core.resources.IProjectNature</tt>. 
      Defines some of the properties that a JET nature has. Implemented by <tt class="code">JETNature</tt>. 
      Used as a filter for project property pages by the <tt class="code">org.eclipse.emf.codegen.ui</tt> 
      plugin.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETAddNatureOperation</tt></td>
    <td>A <tt class="code">org.eclipse.core.resources.IWorkspaceRunnable</tt> for adding the 
      JET nature to a project in the workspace. Used by the <tt class="code">AddJETNatureAction</tt> 
      in the <tt class="code">org.eclipse.emf.codegen.ui</tt> plug-in.</td>

  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETBuilder</tt></td>
    <td>This class extends <tt class="code">org.eclipse.core.resources.IncrementalProjectBuilder</tt>. 
      When its <tt class="code">build</tt> method is invoked, it delegates to <tt class="code">JETCompileTemplateOperation</tt> 
      to translate all templates in the workspace project that have been changed 
      since the previous build. Templates must be located in one of the folders 
      specified as Template Containers in the JET Nature of the project.</td>

  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETCharDataGenerator</tt></td>
    <td>Responsible for a part of the template translation process. Generates 
      strings for the character data present in the template file. Used by <tt class="code">JETCompiler</tt>.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETCompiler</tt></td>

    <td>This is the core class for template translation. This class is responsible 
      for translating templates to the Java source code of a template implementation 
      class. The actual translation is delegated to other classes in this package. 
      A <tt class="code">JETParser</tt> is used to parse the template into template elements. 
      <tt class="code">JETCompiler</tt> implements the <tt class="code">JETParseEventListener</tt> interface 
      and registers itself with the parser to be notified when the parser recognizes 
      a template element. For every recognized template element, <tt class="code">JETCompiler</tt> 
      uses a <tt class="code">JETGenerator</tt> to translate the template element to Java source 
      code. When the template parsing is complete, <tt class="code">JETCompiler</tt> uses a 
      <tt class="code">JETSkeleton</tt> to assemble the Java source code elements to a single 
      compilation unit (a Java class).</td>

  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETCompileTemplateOperation</tt></td>
    <td>This class implements <tt class="code">org.eclipse.core.resources.IWorkspaceRunnable</tt> 
      so it can execute as a batch operation within the workspace. This operation 
      takes a workspace project, one or more Template Containers and optionally 
      a list of specific template files as constructor parameters. When its <tt class="code">run</tt> 
      method is invoked, it uses a <tt class="code">JETCompiler</tt> to translate the template 
      files in the specified workspace project folders to Java source files for 
      template implementation classes. This operation can optionally be configured 
      to trigger a complete build of the project when it is finished to compile 
      the Java source files to <i>.class</i> files.</td>

  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETConstantDataGenerator</tt></td>
    <td>Responsible for a part of the template translation process. Extends <tt class="code">JETCharDataGenerator</tt> 
      to generate constant declarations for the strings with character data present 
      in the template file.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETCoreElement</tt></td>

    <td>Interface for core JET syntax elements (directive, expression, scriptlet 
      and quote-escape). Used by <tt class="code">JETParser</tt>.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETEmitter</tt></td>
    <td>This class provides a convenient high-level API for users of this package. 
      The <tt class="code">generate</tt> method of this class translates a template to Java 
      source code, compiles this source code to a template implementation class, 
      asks the template class to generate text and finally returns the generated 
      result. This class creates a Java project called <i>.JETEmitters</i> in 
      the workspace, translates the template into this project, and simply calls 
      <tt class="code">build</tt> on the <i>.JETEmitters</i> project to compile the source 
      code. If translation or compilation fails, a <tt class="code">JETException</tt> is thrown. 
      A template implementation Java class is "executed" by calling its <tt class="code">generate</tt> 
      method.</td>

  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETException</tt></td>
    <td>Extends <tt class="code">org.eclipse.core.runtime.CoreException</tt>, but provides 
      more convenient constructors.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETExpressionGenerator</tt></td>

    <td>Responsible for a part of the template translation process. Extends <tt class="code">JETScriptletGenerator</tt> 
      to translate JET expressions (<tt class="code">&lt;%= ... %&gt;</tt> stuff) to Java source 
      code.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETGenerator</tt></td>
    <td>Interface for generators: classes that know how to translate part of a 
      JET template to a Java source code element.</td>

  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETMark</tt></td>
    <td>A state object used by the <tt class="code">JETParser</tt> to mark points in the JET 
      character input stream, and delegate the processing of parts of the stream 
      to other objects.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETNature</tt></td>

    <td> 
      <p>This class implements <tt class="code">IJETNature</tt> so that it can configure 
        a workspace project with the JET Nature. When this nature is added to 
        a project, it adds a JET Builder to the front of the build spec of the 
        project. This nature defines two properties: </p>
      <ul>
        <li> Template Containers - a list of folders in the project that contain 
          the JET templates to translate. </li>
        <li>Source Container - the target folder in which to save translated template 
          implementation Java classes. </li>
      </ul>

      <p>These properties are used by the JET Builder when performing a build.</p>
    </td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETParseEventListener</tt></td>
    <td>Interface for objects that know how to process parts of a JET character 
      input stream.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETParser</tt></td>

    <td>The main parser class. Has several inner classes for recognizing core 
      JET syntax elements (directive, expression, scriptlet and quote-escape). 
      When a core JET syntax element is recognized, the actual processing of the 
      element is delegated to a <tt class="code">JETParseEventListener</tt>.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETReader</tt></td>
    <td>An input buffer for the JET parser. Provides a <tt class="code">stackStream</tt> method 
      that others can call with the character stream to an include file. Also 
      provides many other convenience methods for the parser.</td>

  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETScriptletGenerator</tt></td>
    <td>Responsible for a part of the template translation process. Translates 
      JET scriptlets (<tt class="code">&lt;% ... %&gt;</tt> stuff) to Java source code.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JETSkeleton</tt></td>

    <td>This class provides an interface for assembling Java source code elements 
      into a single Java compilation unit (a Java class). Java source code elements 
      are assembled according to a class skeleton definition. A skeleton can be 
      used to add boilerplate code to a translated template implementation class. 
      This class provides a default custom template implementation class skeleton 
      definition, but can also assemble Java elements using a custom skeleton. 
      The actual parsing and generation of Java source code is delegated to classes 
      in the <tt class="code">org.eclipse.jdt.core.jdom</tt> package.</td>
  </tr>
  </tbody>
</table>
<p></p>
<b>Package org.eclipse.emf.codegen.jmerge</b> 
<p></p>
<table border="1" cellspacing="0">
  <tbody> 
  <tr> 
    <td><b>Class</b></td>

    <td><b>Description</b></td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JControlModel</tt></td>
    <td>A control model that provides dictionaries and rules to drive a merge 
      process.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JMerger</tt></td>

    <td>A class for merging Java source files. Uses classes in the <tt class="code">org.eclipse.jdt.core.jdom</tt> 
      package to parse the source code. This class can be used by application 
      code, but can also be run as an Eclipse headless application.</td>
  </tr>
  <tr> 
    <td valign="top"><tt class="code">JPatternDictionary</tt></td>
    <td>A dictionary of signatures and JDOM nodes.</td>
  </tr>

  <tr> 
    <td valign="top"><tt class="code">PropertyMerger</tt></td>
    <td>A class for merging property files. This class can be used by application 
      code, but can also be run as an Eclipse headless application.</td>
  </tr>
  </tbody>
</table>
<p></p>
<h3><a name="codegen_headless_application"></a>Running CodeGen as an Eclipse Headless 
  Application </h3>
<p>The <tt class="code">org.eclipse.emf.codegen.CodeGen</tt> class can translate a JET template to Java source code 
  and optionally merge the template implementation Java source code with an existing 
  Java class. CodeGen can be used as an Eclipse headless application ("headless" 
  means that the Eclipse GUI does not start). The <tt class="code">plugins/org.eclipse.emf.codegen/test</tt> 
  folder in your Eclipse installation contains some scripts for launching the 
  CodeGen class as an Eclipse headless application. These scripts are in Unix 
  format.</p>

<p><img src="images/win_only.gif" width="49" height="13"/> Below is an example 
  script for Windows. Note that we pass two arguments to the CodeGen class:</p>
<ul>
  <li>the <img src="images/tag_1.gif" width="24" height="13"/>uri of the template 
    to translate </li>
  <li>the <img src="images/tag_2.gif" width="24" height="13"/>target path where 
    the translation result should be saved </li>
</ul>
<p>If the target path already contains a previous translation result, and you 
  want to merge the new translation result with the existing one, you can specify 
  a <tt class="code">JMerge</tt> control model file as the third argument. The <tt class="code">plugins/org.eclipse.emf.codegen/test</tt> 
  folder in your Eclipse installation contains an example <tt class="code">merge.xml</tt> file.</p>

<pre class="code">   @echo off
   set ECLIPSE_HOME=C:\eclipse-2.1\eclipse
   set WORKSPACE=%ECLIPSE_HOME%\workspace
   set OPTS=-Xmx900M -Djava.compiler=NONE -verify -cp %ECLIPSE_HOME%\startup.jar
   set MAIN=org.eclipse.core.launcher.Main -noupdate -data %WORKSPACE% 
 
<img src="images/tag_1.gif" width="24" height="13"/>set TEMPLATE_URI=test.javajet
<img src="images/tag_2.gif" width="24" height="13"/>set TARGET_FOLDER=C:\temp\jetstandalone\MyProject
   set ARGUMENTS=%TEMPLATE_URI% %TARGET_FOLDER%
   
   echo Shut down Eclipse before running this script.
   java %OPTS% %MAIN% -application org.eclipse.emf.codegen.CodeGen %ARGUMENTS%
</pre>
<h3><a name="jetc"></a>jetc: An ANT Task for Translating JET Templates Outside 
  of Eclipse </h3>
<p>Author: Knut Wannheden (knut.wannheden at paranor.ch) </p>
<p>Binary: <a href="jetc-task.jar">jetc-task.jar</a>. </p>
<p>The source: <a href="JETCTask.java" target=_blank>JETCTask.java</a>.</p>

<p>Some notes: </p>
<ul>
  <li>In the <tt class="code">&lt;taskdef/&gt;</tt> you have to specify the classpath to include 
    both this task as well as the jars of a number of Eclipse plug-ins (see the 
    example buildfile). </li>
  <li>There are two ways to tell the jetc task which template(s) it should translate: 
  </li>
  <ul>
    <li>Use a nested fileset to specify the directory containing the template 
      files. </li>

    <li>Specify the template uri in the "template" attribute of the task. When 
      used this way, the task supports the "class" and "package" attributes which 
      overload the JET directives "class" and "package" in the template. It can 
      also be used if the JET directive is missing altogether. Use this attribute 
      when you want to specify the class to generate outside the template. </li>
  </ul>
</ul>
<p>Here's a simple Ant buildfile (the taskdef classpath assumes you have Eclipse 
  2.1 and EMF 1.1.0): </p>
<pre class="code"> &lt;project default="jetc_multiple_templates"&gt;
  
  &lt;property name="eclipse.plugins.dir" location="C:/eclipse-2.1/eclipse/plugins"/&gt;
  
  &lt;taskdef name="jetc" classname="ch.paranor.epla.structure.JETCTask"&gt;

    &lt;classpath&gt;
      &lt;pathelement location="jetc-task.jar"/&gt;
      &lt;fileset dir="${eclipse.plugins.dir}"&gt;
        &lt;include name="org.eclipse.core.boot_2.1.0/boot.jar"/&gt;
        &lt;include name="org.eclipse.core.resources_2.1.0/resources.jar"/&gt;
        &lt;include name="org.eclipse.core.runtime_2.1.0/runtime.jar"/&gt;

        &lt;include name="org.eclipse.emf.codegen_1.1.0/runtime/codegen.jar"/&gt;
        &lt;include name="org.eclipse.jdt.core_2.1.0/jdtcore.jar"/&gt;
      &lt;/fileset&gt;
    &lt;/classpath&gt;
  &lt;/taskdef&gt;
  
  &lt;!-- Usage example 1: --&gt;

  &lt;!-- Specify the template file in the "template" attribute. --&gt;
  &lt;!-- You can use the "class" and "package" attributes to override the --&gt;
  &lt;!-- "class" and "package" attributes in the template file. --&gt;
  &lt;target name="jetc_single_template"&gt;
    &lt;mkdir dir="jet-output"/&gt;
    &lt;jetc template="test.xmljet" package="com.foo" class="Test" destdir="jet-output"/&gt;

    &lt;javac srcdir="jet-output" destdir="classes"/&gt;
  &lt;/target&gt;
 
  &lt;!-- Usage example 2: --&gt;
  &lt;!-- Translate a bunch of template files at once. --&gt;
  &lt;!-- You cannot use the "class" and "package" attributes when using a fileset. --&gt;
  &lt;target name="jetc_multiple_templates"&gt;

    &lt;mkdir dir="jet-output"/&gt;
    &lt;jetc destdir="jet-output"&gt;
      &lt;fileset dir="jet-templates" includes="*.*jet"/&gt;
    &lt;/jetc&gt;
    &lt;javac srcdir="jet-output" destdir="classes"/&gt;
  &lt;/target&gt;

  
 &lt;/project&gt;</pre>
<h2>Resources </h2>
<p><a href="http://developer.java.sun.com/developer/Books/shiftintojava/page1.html#replaceenums" target="_blank">Substitutes 
  for Missing C Constructs</a> (By Joshua Bloch)</p>
<a href="http://www.javaworld.com/javaworld/javatips/jw-javatip122.html" target="_blank"> 
Java Tip 122: Beware of Java typesafe enumerations</a> (By Vladimir Roubtsov)<br/>
<p><a href="http://www.javaworld.com/javaworld/javatips/jw-javatip133.html" target="_blank">Java 
  Tip 133: More on typesafe enums</a> (By Philip Bishop)</p>

<p><a href="http://www.eclipse.org/emf/">http://www.eclipse.org/emf/ </a></p>
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