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 <DIV align=right>&nbsp; <FONT face="Times New Roman, Times, serif"
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     <TD align=left bgColor=#0080c0 colSpan=2 vAlign=top><B><FONT
       face=Arial,Helvetica><FONT color=#ffffff>&nbsp;Eclipse Corner
       Article</FONT></FONT></B></TD></TR></TBODY></TABLE>
 <H1><img align=center
 src="Idea.jpg" width="120" height="86">
 <center>Preferences in the Eclipse Workbench UI</center></H1>
 <blockquote>
 <b>Summary</b><br>
 In the Eclipse Platform plug-in developers define preference pages for their plug-ins
 for use in the Workbench Preferences Dialog. This article explains when to use a
 preference and some of the features the Eclipse Platform provides to support
 preferences.
 <p><b>By Tod Creasey, OTI<br>
     </b> December 15, 2001</p>
 </blockquote>
 <HR width="100%">

 <h2>Introduction</h2>
 <p>The Eclipse Platform has support for user defined preferences that are
 persisted along with the workbench. This article will discuss what type of data
 should be stored as a preference and will show how to develop and register a
 user interface to allow the user to set these preferences. It will also cover
 how to initialize and retrieve preferences for use by other other plug-ins that
 use your plug-in. This functionality will be shown using an example that
 searches documents for bad words. We will set our preferences for this tool
 using two preference pages, one simple one to set a highlight color and one more
 complex one to set the list of words.
 </p>
 <h2>When to Use a Preference
 </h2>
 <p>A preference is data that is persisted between workbench sessions to allow
 the user to keep the state of a plug-in consistent between Eclipse sessions. Typical preferences are
 default values for new instances, colors for editors and paths, or processing
 information for operations performed on data (such as a build path for a Java&trade;
 file).
 </p>
 <p>Preferences are not intended to reference any resource currently defined in
 the workspace and instead should be used for editors, views or other objects that
 perform operations on a resource. Data persisted on a resource instance is better suited to be
 a property which will be discussed in a later article.
 </p>
 <p>A preference can be made available to any plug-in that has your plug-in as a
 prerequisite. The usual way to do that is to provide API on your plug-in that
 allows for access to the preferences you want to make available. The values of
 these preferences are stored in the .metadata/.plugins directory of the
 workbench on a per plug-in basis. We demonstrate
 how to do this below.
 </p>
 <h2>The Preference Store and the Plug-in</h2>
 <p>Every UI plug-in has it's own preference store provided by the workbench. For
   this example we will define a plug-in and use its preference store for our preferences.
   As we are going to use this plug-in within the UI we define it as a subclass
   of AbstractUIPlugin. Our constructor (see <img border="0" src="tag_2.gif" width="24" height="13">)
   will create a singleton to allow easy access to the plug-in instance in the
   workbench. We also implement the method initializeDefaultPreferences() to set
   up our default values for our two preferences. We are defining a preference
   for the bad words and a preference for the color of the highlight. Each preference
   value is looked up using a given key. In the code below the keys we are using
   are defined by the constants in <img src="tag_1.gif" width="24" height="13">.
 </p>
 <p>The default value should be set for all preferences to be sure that there is
   a value to use at all times. A default value also ensures that the UI can provide
   a way to reset a preference value back to a reasonable initial setting via the
   Restore Defaults button.The default value of the preference should be initialized
   in the plug-in so that it is set before any of the UI is created.&nbsp; </p>
 <p> IAbstractWorkbenchPlugin defines a method called initializeDefaultPreferences(IPreferenceStore)
   which is called when the preference store is created the first time. In this
   method (see <img border="0" src="tag_3.gif" width="24" height="13">) you should
   set the default value for all values that you will be using the preference store
   for. We set a default color using the helper methods in the PreferenceConverter
   which allows the plug-in developer to set and get values for a preference of
   commonly stored types like FontData, Point etc. This API is provided because
   preferences are stored and retrieved as Strings in a human readable format in
   order to leverage the java properties mechanism.&nbsp; Our more complex bad
   words preference is initialized using a set of preselected bad words defined
   in the format we are going to store them in as we do not have API on the PreferenceConvertor
   to store or retreive arrays of Strings.</p>
 <pre>Color color= Display.getDefault().getSystemColor(SWT.COLOR_BLUE);
 PreferenceConverter.setDefault(store, HIGHLIGHT_PREFERENCE, color.getRGB());</pre>
 <pre>public class BadWordCheckerPlugin extends AbstractUIPlugin {
 	//The shared instance.
 	private static BadWordCheckerPlugin plugin;

 	//The identifiers for the preferences
 <img border="0" src="tag_1.gif" width="24" height="13">	public static final String BAD_WORDS_PREFERENCE =
 		&quot;org.eclipse.ui.articles.badwordchecker.badwords&quot;;
 	public static final String HIGHLIGHT_PREFERENCE =
 		&quot;org.eclipse.ui.articles.badwordchecker.highlight&quot;;

 	//The default values for the preferences
 	public static final String DEFAULT_BAD_WORDS = &quot;bug;bogus;hack;&quot;;
 	public static final int DEFAULT_HIGHLIGHT = SWT.COLOR_BLUE;

 	/**
 	 * The constructor.
 	 */
 	public BadWordCheckerPlugin(IPluginDescriptor descriptor) {
 		super(descriptor);
 <img border="0" src="tag_2.gif" width="24" height="13">		plugin = this;
 	}

 	/**
 	 * Returns the shared instance.
 	 */
 	public static BadWordCheckerPlugin getDefault() {
 		return plugin;
 	}

 	/**
 	 * Initializes a preference store with default preference values
 	 * for this plug-in.
 	 * @param store the preference store to fill
 	 */
 	protected void initializeDefaultPreferences(IPreferenceStore store) {
 <img border="0" src="tag_3.gif" width="24" height="13">		store.setDefault(BAD_WORDS_PREFERENCE, DEFAULT_BAD_WORDS);
 		Color color= Display.getDefault().getSystemColor(DEFAULT_HIGHLIGHT);
 		PreferenceConverter.setDefault(store,  HIGHLIGHT_PREFERENCE, color.getRGB());

 	}
 }</pre>
 <h2>Defining Preference Pages in plugin.xml</h2>
 <p>Now that we have defined the preference we want to provide a way for the user
 to set the preference value. Preference pages for the workbench can be found in
 the preferences dialog. The preferences dialog is accessible via the Window-&gt;Preferences
 menu group. Plug-in developers should add their preference pages to this dialog using the plugin.xml of their
 plug-in in order to maintain a consistent look and feel with other Eclipse
 plug-ins. The definition of the preference pages within plugin.xml looks like
 this:
 </p>
 <pre>&lt;extension point=&quot;org.eclipse.ui.preferencePages&quot;&gt;
  	&lt;page id=&quot;org.eclipse.ui.articles.BadWordsPreference&quot;
 <img border="0" src="tag_1.gif" width="24" height="13"> 		name=&quot;Bad Words&quot;
 <img border="0" src="tag_2.gif" width="24" height="13">    		class=&quot;org.eclipse.ui.articles.badwordchecker.BadWordsPreferencePage&quot;&gt;
    	&lt;/page&gt;

  	&lt;page id=&quot;org.eclipse.ui.articles.BadWordsColorPreference&quot;
   	      	name=&quot;Colors&quot;
 	      	class=&quot;org.eclipse.ui.articles.badwordchecker.BadWordsColorPreferencePage&quot;
 <img border="0" src="tag_3.gif" width="24" height="13">		category=&quot;org.eclipse.ui.articles.BadWordsPreference&quot;&gt;
    	&lt;/page&gt;
 &lt;/extension&gt;</pre>
 <p>The definition above sets the name (<img border="0" src="tag_1.gif" width="24" height="13">)
 of the preference page for use in the list
 of pages in the preference dialog and also specifies the class(<img border="0" src="tag_2.gif" width="24" height="13">) to be
 instantiated for creating the preference page. This class must conform to
 IWorkbenchPreferencePage.</p>
 <p>In the second definition there is a category (<img border="0" src="tag_3.gif" width="24" height="13">)
 tag which is used to make one
 page the child of another in the list in the preferences dialog. Preference
 pages can be stored as the children of other pages. This is useful
 for keeping a series of pages together that are related to each other and also
 reduces the clutter in the workbench preferences page. A page can be made the
 child of another page by setting the id of the parent page as the value of the
 category field in the plugin.xml. A page with no parent is displayed as a child
 with no root.</p>
 <p>With the above declarations in our plugin.xml the list of preference pages
 shown in the preference dialog will look like:</p>
 <p align="center"><img border="0" src="tree.jpg" width="179" height="284"></p>
 <p align="center">The Preference Dialog Tree with the Bad Words and Color Page
 Added</p>
 <h2>The Color Preference Page
 </h2>
 <p>The color preference page is an example of a simple page that uses a single
 JFace field editor to manage its values. Initially a preference page class is
 defined.&nbsp; All
 classes used in the preference dialog must conform to IWorkbenchPreferencePage.
 Eclipse includes the class PreferencePage which implements most of the necessary API
 for a preference page. The class definition for our preference page is:</p>
 <pre>BadWordsColorPreferencePage
 	extends PreferencePage
 	implements IWorkbenchPreferencePage</pre>
 <p>Once we have defined the page we want to initialize it.&nbsp; IWorkbenchPreferencePage
 specifies a message init(IWorkbench) for this purpose. We will not use the Workbench
 argument for this page. Our implementation only sets
 the preference store for the page.</p>
 <pre>public void init(IWorkbench workbench) {
 	//Initialize the preference store we wish to use
 	setPreferenceStore(BadWordCheckerPlugin.getDefault().getPreferenceStore());
 }</pre>
 <p>The other required method we must implement is createContents().
 All we are going to do is use a ColorFieldEditor
 to set our preference. It is also suggested that performDefaults is
 implemented so that the current state can be reset to the defaults defined in
 the plug-in. We also need to implement performOK so that the settings defined by the user are
 stored in the preference store for our plug-in. Our
 implementation is simple as the ColorFieldEditor has the code to load defaults
 and store the results of an apply for a preference already defined and performOK
 and performDefaults can call the corresponding methods on ColorFieldEditor.</p>
 <pre>/**
  * Performs special processing when this page's Restore Defaults button has
  * been pressed.
  * Sets the contents of the color field to the default value in the preference
  * store.
  */
 protected void performDefaults() {
 	colorEditor.loadDefault();
 }
 /**
  * Method declared on IPreferencePage. Save the
  * color preference to the preference store.
  */
 public boolean performOk() {
 	colorEditor.store();
 	return super.performOk();
 }</pre>
 <p>&nbsp;</p>
 <p align="center"><img border="0" src="colorpreference.jpg" width="598" height="541"></p>
 <p align="center">The Color Preference Page</p>
 <h2>The Bad Words Preference Page
 </h2>
 <p>We have seen how to do a simple preference page with just a color and categorize it.
 Now we will show how to use a complex object as a
 preference and still have it persisted by the preference store and editable in a
 preference page. For this example
 we are going to add a bad words preference which is an array of Strings.
 </p>
 <p>As the PreferenceConverter does not have API for conversion of arrays of
 Strings we will implement it ourselves in the BadWordCheckerPlugin.
 By implementing it in the plug-in we put the API for the use of the preference in
 a place visible to all objects that have access to this plug-in. Normally we
 would use the PreferenceConverter for conversion to and from the storage format.</p>
 <p>Methods for getting the default value of the
 preference and a getter and a setter are
 defined first - getBadWordsDefaultPreference (which returns an array of Strings)&nbsp; getBadWordsPreference (which also returns an array of Strings) and
 setBadWordsPreference which takes an array of Strings as its argument. The
 String array is stored in the preference store as a single string separated by semicolons. We choose
 semicolons as this are only ever used as punctuation and will therefore never
 be part of a word we are searching for.</p>
 <pre>/**
  * Return the bad words preference default
  * as an array of Strings.
  * @return String[]
  */
 public String[] getDefaultBadWordsPreference(){
 	return convert(getPreferenceStore().getDefaultString(BAD_WORDS_PREFERENCE));
 }

 /**
  * Return the bad words preference as an array of
  * Strings.
  * @return String[]
  */
 public String[] getBadWordsPreference() {
 	return convert(getPreferenceStore().getString(BAD_WORDS_PREFERENCE));
 }

 /**
  * Convert the supplied PREFERENCE_DELIMITER delimited
  * String to a String array.
  * @return String[]
  */
 private String[] convert(String preferenceValue) {
 	StringTokenizer tokenizer =
 		new StringTokenizer(preferenceValue, PREFERENCE_DELIMITER);
 	int tokenCount = tokenizer.countTokens();
 	String[] elements = new String[tokenCount];
 		for (int i = 0; i &lt; tokenCount; i++) {
 			elements[i] = tokenizer.nextToken();
 	}

 	return elements;
 }

 /**
  * Set the bad words preference
  * @param String [] elements - the Strings to be
  * 	converted to the preference value
  */
 public void setBadWordsPreference(String[] elements) {
 	StringBuffer buffer = new StringBuffer();
 	for (int i = 0; i &lt; elements.length; i++) {
 		buffer.append(elements[i]);
 		buffer.append(PREFERENCE_DELIMITER);
 	}
 	getPreferenceStore().setValue(BAD_WORDS_PREFERENCE, buffer.toString());
 }
 </pre>
 <p>There is no field editor defined in JFace
 for&nbsp; editing String arrays so we will define a list that shows the
 items with widgets to add and remove them. Our performOK method will send the
 current contents of the list to the setBadWordsPreference method and the
 performDefaults method will reset the list of strings to be the result of
 getDefaultBadWordsPreference from BadWordCheckerPlugin. As a List widget takes an array of Strings as its
 content we can use the results of these helper methods directly
 in conjunction with the methods we defined for the bad words preference in the
 plug-in. The performOK and performDefaults for this preference page use these
 methods to update the preference and reset the values in the list widget.
 </p>
 <pre>/**
  * Performs special processing when this page's Restore Defaults button has been pressed.
  * Sets the contents of the nameEntry field to
  * be the default
  */
 protected void performDefaults() {
 	badWordList.setItems(BadWordCheckerPlugin.getDefault().getDefaultBadWordsPreference());
 }
 /**
  * Method declared on IPreferencePage. Save the
  * author name to the preference store.
  */
 public boolean performOk() {
 	BadWordCheckerPlugin.getDefault().setBadWordsPreference(badWordList.getItems());
 	return super.performOk();
 }</pre>
 <p align="center"><img border="0" src="badwordpreference.jpg" width="596" height="539">
 </p>
 <p align="center">The Bad Word Preference Dialog
 </p>
 <h2>Conclusions
 </h2>
 <p>In this article we have demonstrated how to use the preferences store and
 preferences pages provided by Eclipse to allow a plug-in to maintain and update
 preferences between Eclipse sessions. By use of the preference store in
 conjunction with the preferences dialog and provided field editors a plug-in
 developer can quickly put together a user interface for managing preferences. To
 find out more about the preferences that Eclipse provides see the Platform
 Plug-in Developers Guide in the Help Perspective. The help information is in the
 Programmers Guide Preferences and Properties section.
 </p>
 <p>The full implementation of the example in this article can be found in <a href="preferences.zip">preferences.zip</a>.
 </p>

 <p><small>Java and all Java-based trademarks and logos are trademarks or registered
 trademarks of Sun Microsystems, Inc. in the United States, other countries, or
 both.</small></p>

 </body>

 </html>
	<html>

	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">


	<title>Preferences and Properties in the Eclipse Workbench UI</title>
	<link rel="stylesheet" type="text/css" href="default_style.css">
	</head>

	<body>
	<DIV align=right>  <FONT face="Times New Roman, Times, serif"
	size=2>Copyright © 2001 Object Technology International, Inc.</FONT> </DIV>
	<TABLE border=0 cellPadding=2 cellSpacing=0 width="100%">
	<TBODY>
	<TR>
	<TD align=left bgColor=#0080c0 colSpan=2 vAlign=top><B><FONT
	face=Arial,Helvetica><FONT color=#ffffff> Eclipse Corner
	Article</FONT></FONT></B></TD></TR></TBODY></TABLE>
	<H1><img align=center
	src="Idea.jpg" width="120" height="86">
	<center>Preferences in the Eclipse Workbench UI</center></H1>
	<blockquote>
	<b>Summary</b><br>
	In the Eclipse Platform plug-in developers define preference pages for their plug-ins
	for use in the Workbench Preferences Dialog. This article explains when to use a
	preference and some of the features the Eclipse Platform provides to support
	preferences.
	<p><b>By Tod Creasey, OTI<br>
	</b> December 15, 2001</p>
	</blockquote>
	<HR width="100%">

	<h2>Introduction</h2>
	<p>The Eclipse Platform has support for user defined preferences that are
	persisted along with the workbench. This article will discuss what type of data
	should be stored as a preference and will show how to develop and register a
	user interface to allow the user to set these preferences. It will also cover
	how to initialize and retrieve preferences for use by other other plug-ins that
	use your plug-in. This functionality will be shown using an example that
	searches documents for bad words. We will set our preferences for this tool
	using two preference pages, one simple one to set a highlight color and one more
	complex one to set the list of words.
	</p>
	<h2>When to Use a Preference
	</h2>
	<p>A preference is data that is persisted between workbench sessions to allow
	the user to keep the state of a plug-in consistent between Eclipse sessions. Typical preferences are
	default values for new instances, colors for editors and paths, or processing
	information for operations performed on data (such as a build path for a Java™
	file).
	</p>
	<p>Preferences are not intended to reference any resource currently defined in
	the workspace and instead should be used for editors, views or other objects that
	perform operations on a resource. Data persisted on a resource instance is better suited to be
	a property which will be discussed in a later article.
	</p>
	<p>A preference can be made available to any plug-in that has your plug-in as a
	prerequisite. The usual way to do that is to provide API on your plug-in that
	allows for access to the preferences you want to make available. The values of
	these preferences are stored in the .metadata/.plugins directory of the
	workbench on a per plug-in basis. We demonstrate
	how to do this below.
	</p>
	<h2>The Preference Store and the Plug-in</h2>
	<p>Every UI plug-in has it's own preference store provided by the workbench. For
	this example we will define a plug-in and use its preference store for our preferences.
	As we are going to use this plug-in within the UI we define it as a subclass
	of AbstractUIPlugin. Our constructor (see <img border="0" src="tag_2.gif" width="24" height="13">)
	will create a singleton to allow easy access to the plug-in instance in the
	workbench. We also implement the method initializeDefaultPreferences() to set
	up our default values for our two preferences. We are defining a preference
	for the bad words and a preference for the color of the highlight. Each preference
	value is looked up using a given key. In the code below the keys we are using
	are defined by the constants in <img src="tag_1.gif" width="24" height="13">.
	</p>
	<p>The default value should be set for all preferences to be sure that there is
	a value to use at all times. A default value also ensures that the UI can provide
	a way to reset a preference value back to a reasonable initial setting via the
	Restore Defaults button.The default value of the preference should be initialized
	in the plug-in so that it is set before any of the UI is created.  </p>
	<p> IAbstractWorkbenchPlugin defines a method called initializeDefaultPreferences(IPreferenceStore)
	which is called when the preference store is created the first time. In this
	method (see <img border="0" src="tag_3.gif" width="24" height="13">) you should
	set the default value for all values that you will be using the preference store
	for. We set a default color using the helper methods in the PreferenceConverter
	which allows the plug-in developer to set and get values for a preference of
	commonly stored types like FontData, Point etc. This API is provided because
	preferences are stored and retrieved as Strings in a human readable format in
	order to leverage the java properties mechanism.  Our more complex bad
	words preference is initialized using a set of preselected bad words defined
	in the format we are going to store them in as we do not have API on the PreferenceConvertor
	to store or retreive arrays of Strings.</p>
	<pre>Color color= Display.getDefault().getSystemColor(SWT.COLOR_BLUE);
	PreferenceConverter.setDefault(store, HIGHLIGHT_PREFERENCE, color.getRGB());</pre>
	<pre>public class BadWordCheckerPlugin extends AbstractUIPlugin {
	//The shared instance.
	private static BadWordCheckerPlugin plugin;

	//The identifiers for the preferences
	<img border="0" src="tag_1.gif" width="24" height="13"> public static final String BAD_WORDS_PREFERENCE =
	"org.eclipse.ui.articles.badwordchecker.badwords";
	public static final String HIGHLIGHT_PREFERENCE =
	"org.eclipse.ui.articles.badwordchecker.highlight";

	//The default values for the preferences
	public static final String DEFAULT_BAD_WORDS = "bug;bogus;hack;";
	public static final int DEFAULT_HIGHLIGHT = SWT.COLOR_BLUE;

	/**
	* The constructor.
	*/
	public BadWordCheckerPlugin(IPluginDescriptor descriptor) {
	super(descriptor);
	<img border="0" src="tag_2.gif" width="24" height="13"> plugin = this;
	}

	/**
	* Returns the shared instance.
	*/
	public static BadWordCheckerPlugin getDefault() {
	return plugin;
	}

	/**
	* Initializes a preference store with default preference values
	* for this plug-in.
	* @param store the preference store to fill
	*/
	protected void initializeDefaultPreferences(IPreferenceStore store) {
	<img border="0" src="tag_3.gif" width="24" height="13"> store.setDefault(BAD_WORDS_PREFERENCE, DEFAULT_BAD_WORDS);
	Color color= Display.getDefault().getSystemColor(DEFAULT_HIGHLIGHT);
	PreferenceConverter.setDefault(store, HIGHLIGHT_PREFERENCE, color.getRGB());

	}
	}</pre>
	<h2>Defining Preference Pages in plugin.xml</h2>
	<p>Now that we have defined the preference we want to provide a way for the user
	to set the preference value. Preference pages for the workbench can be found in
	the preferences dialog. The preferences dialog is accessible via the Window->Preferences
	menu group. Plug-in developers should add their preference pages to this dialog using the plugin.xml of their
	plug-in in order to maintain a consistent look and feel with other Eclipse
	plug-ins. The definition of the preference pages within plugin.xml looks like
	this:
	</p>
	<pre><extension point="org.eclipse.ui.preferencePages">
	<page id="org.eclipse.ui.articles.BadWordsPreference"
	<img border="0" src="tag_1.gif" width="24" height="13"> name="Bad Words"
	<img border="0" src="tag_2.gif" width="24" height="13"> class="org.eclipse.ui.articles.badwordchecker.BadWordsPreferencePage">
	</page>

	<page id="org.eclipse.ui.articles.BadWordsColorPreference"
	name="Colors"
	class="org.eclipse.ui.articles.badwordchecker.BadWordsColorPreferencePage"
	<img border="0" src="tag_3.gif" width="24" height="13"> category="org.eclipse.ui.articles.BadWordsPreference">
	</page>
	</extension></pre>
	<p>The definition above sets the name (<img border="0" src="tag_1.gif" width="24" height="13">)
	of the preference page for use in the list
	of pages in the preference dialog and also specifies the class(<img border="0" src="tag_2.gif" width="24" height="13">) to be
	instantiated for creating the preference page. This class must conform to
	IWorkbenchPreferencePage.</p>
	<p>In the second definition there is a category (<img border="0" src="tag_3.gif" width="24" height="13">)
	tag which is used to make one
	page the child of another in the list in the preferences dialog. Preference
	pages can be stored as the children of other pages. This is useful
	for keeping a series of pages together that are related to each other and also
	reduces the clutter in the workbench preferences page. A page can be made the
	child of another page by setting the id of the parent page as the value of the
	category field in the plugin.xml. A page with no parent is displayed as a child
	with no root.</p>
	<p>With the above declarations in our plugin.xml the list of preference pages
	shown in the preference dialog will look like:</p>
	<p align="center"><img border="0" src="tree.jpg" width="179" height="284"></p>
	<p align="center">The Preference Dialog Tree with the Bad Words and Color Page
	Added</p>
	<h2>The Color Preference Page
	</h2>
	<p>The color preference page is an example of a simple page that uses a single
	JFace field editor to manage its values. Initially a preference page class is
	defined.  All
	classes used in the preference dialog must conform to IWorkbenchPreferencePage.
	Eclipse includes the class PreferencePage which implements most of the necessary API
	for a preference page. The class definition for our preference page is:</p>
	<pre>BadWordsColorPreferencePage
	extends PreferencePage
	implements IWorkbenchPreferencePage</pre>
	<p>Once we have defined the page we want to initialize it.  IWorkbenchPreferencePage
	specifies a message init(IWorkbench) for this purpose. We will not use the Workbench
	argument for this page. Our implementation only sets
	the preference store for the page.</p>
	<pre>public void init(IWorkbench workbench) {
	//Initialize the preference store we wish to use
	setPreferenceStore(BadWordCheckerPlugin.getDefault().getPreferenceStore());
	}</pre>
	<p>The other required method we must implement is createContents().
	All we are going to do is use a ColorFieldEditor
	to set our preference. It is also suggested that performDefaults is
	implemented so that the current state can be reset to the defaults defined in
	the plug-in. We also need to implement performOK so that the settings defined by the user are
	stored in the preference store for our plug-in. Our
	implementation is simple as the ColorFieldEditor has the code to load defaults
	and store the results of an apply for a preference already defined and performOK
	and performDefaults can call the corresponding methods on ColorFieldEditor.</p>
	<pre>/**
	* Performs special processing when this page's Restore Defaults button has
	* been pressed.
	* Sets the contents of the color field to the default value in the preference
	* store.
	*/
	protected void performDefaults() {
	colorEditor.loadDefault();
	}
	/**
	* Method declared on IPreferencePage. Save the
	* color preference to the preference store.
	*/
	public boolean performOk() {
	colorEditor.store();
	return super.performOk();
	}</pre>
	<p> </p>
	<p align="center"><img border="0" src="colorpreference.jpg" width="598" height="541"></p>
	<p align="center">The Color Preference Page</p>
	<h2>The Bad Words Preference Page
	</h2>
	<p>We have seen how to do a simple preference page with just a color and categorize it.
	Now we will show how to use a complex object as a
	preference and still have it persisted by the preference store and editable in a
	preference page. For this example
	we are going to add a bad words preference which is an array of Strings.
	</p>
	<p>As the PreferenceConverter does not have API for conversion of arrays of
	Strings we will implement it ourselves in the BadWordCheckerPlugin.
	By implementing it in the plug-in we put the API for the use of the preference in
	a place visible to all objects that have access to this plug-in. Normally we
	would use the PreferenceConverter for conversion to and from the storage format.</p>
	<p>Methods for getting the default value of the
	preference and a getter and a setter are
	defined first - getBadWordsDefaultPreference (which returns an array of Strings)  getBadWordsPreference (which also returns an array of Strings) and
	setBadWordsPreference which takes an array of Strings as its argument. The
	String array is stored in the preference store as a single string separated by semicolons. We choose
	semicolons as this are only ever used as punctuation and will therefore never
	be part of a word we are searching for.</p>
	<pre>/**
	* Return the bad words preference default
	* as an array of Strings.
	* @return String[]
	*/
	public String[] getDefaultBadWordsPreference(){
	return convert(getPreferenceStore().getDefaultString(BAD_WORDS_PREFERENCE));
	}

	/**
	* Return the bad words preference as an array of
	* Strings.
	* @return String[]
	*/
	public String[] getBadWordsPreference() {
	return convert(getPreferenceStore().getString(BAD_WORDS_PREFERENCE));
	}

	/**
	* Convert the supplied PREFERENCE_DELIMITER delimited
	* String to a String array.
	* @return String[]
	*/
	private String[] convert(String preferenceValue) {
	StringTokenizer tokenizer =
	new StringTokenizer(preferenceValue, PREFERENCE_DELIMITER);
	int tokenCount = tokenizer.countTokens();
	String[] elements = new String[tokenCount];
	for (int i = 0; i < tokenCount; i++) {
	elements[i] = tokenizer.nextToken();
	}

	return elements;
	}

	/**
	* Set the bad words preference
	* @param String [] elements - the Strings to be
	* converted to the preference value
	*/
	public void setBadWordsPreference(String[] elements) {
	StringBuffer buffer = new StringBuffer();
	for (int i = 0; i < elements.length; i++) {
	buffer.append(elements[i]);
	buffer.append(PREFERENCE_DELIMITER);
	}
	getPreferenceStore().setValue(BAD_WORDS_PREFERENCE, buffer.toString());
	}
	</pre>
	<p>There is no field editor defined in JFace
	for  editing String arrays so we will define a list that shows the
	items with widgets to add and remove them. Our performOK method will send the
	current contents of the list to the setBadWordsPreference method and the
	performDefaults method will reset the list of strings to be the result of
	getDefaultBadWordsPreference from BadWordCheckerPlugin. As a List widget takes an array of Strings as its
	content we can use the results of these helper methods directly
	in conjunction with the methods we defined for the bad words preference in the
	plug-in. The performOK and performDefaults for this preference page use these
	methods to update the preference and reset the values in the list widget.
	</p>
	<pre>/**
	* Performs special processing when this page's Restore Defaults button has been pressed.
	* Sets the contents of the nameEntry field to
	* be the default
	*/
	protected void performDefaults() {
	badWordList.setItems(BadWordCheckerPlugin.getDefault().getDefaultBadWordsPreference());
	}
	/**
	* Method declared on IPreferencePage. Save the
	* author name to the preference store.
	*/
	public boolean performOk() {
	BadWordCheckerPlugin.getDefault().setBadWordsPreference(badWordList.getItems());
	return super.performOk();
	}</pre>
	<p align="center"><img border="0" src="badwordpreference.jpg" width="596" height="539">
	</p>
	<p align="center">The Bad Word Preference Dialog
	</p>
	<h2>Conclusions
	</h2>
	<p>In this article we have demonstrated how to use the preferences store and
	preferences pages provided by Eclipse to allow a plug-in to maintain and update
	preferences between Eclipse sessions. By use of the preference store in
	conjunction with the preferences dialog and provided field editors a plug-in
	developer can quickly put together a user interface for managing preferences. To
	find out more about the preferences that Eclipse provides see the Platform
	Plug-in Developers Guide in the Help Perspective. The help information is in the
	Programmers Guide Preferences and Properties section.
	</p>
	<p>The full implementation of the example in this article can be found in <a href="preferences.zip">preferences.zip</a>.
	</p>

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