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        <b>Trail:</b> Creating a GUI with JFC/Swing
        <br><b>Lesson:</b> Writing Event Listeners
        <br><b>Section:</b> Implementing Listeners for Commonly Handled Events
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            <div class="linkLESSON"><a href="index.html">Writing Event Listeners</a></div>
<div class="linkAHEAD"><a href="intro.html">Introduction to Event Listeners</a></div>
<div class="linkAHEAD"><a href="generalrules.html">General Information about Writing Event Listeners</a></div>
<div class="linkAHEAD"><a href="eventsandcomponents.html">Listeners Supported by Swing Components</a></div>
<div class="linkAHEAD"><a href="handling.html">Implementing Listeners for Commonly Handled Events</a></div>
<div class="linkBHEAD"><a href="actionlistener.html">How to Write an Action Listener</a></div>
<div class="nolinkBHEAD">How to Write a Caret Listener</div>
<div class="linkBHEAD"><a href="changelistener.html">How to Write a Change Listener</a></div>
<div class="linkBHEAD"><a href="componentlistener.html">How to Write a Component Listener</a></div>
<div class="linkBHEAD"><a href="containerlistener.html">How to Write a Container Listener</a></div>
<div class="linkBHEAD"><a href="documentlistener.html">How to Write a Document Listener</a></div>
<div class="linkBHEAD"><a href="focuslistener.html">How to Write a Focus Listener</a></div>
<div class="linkBHEAD"><a href="internalframelistener.html">How to Write an Internal Frame Listener</a></div>
<div class="linkBHEAD"><a href="itemlistener.html">How to Write an Item Listener</a></div>
<div class="linkBHEAD"><a href="keylistener.html">How to Write a Key Listener</a></div>
<div class="linkBHEAD"><a href="listdatalistener.html">How to Write a List Data Listener</a></div>
<div class="linkBHEAD"><a href="listselectionlistener.html">How to Write a List Selection Listener</a></div>
<div class="linkBHEAD"><a href="mouselistener.html">How to Write a Mouse Listener</a></div>
<div class="linkBHEAD"><a href="mousemotionlistener.html">How to Write a Mouse-Motion Listener</a></div>
<div class="linkBHEAD"><a href="mousewheellistener.html">How to Write a Mouse-Wheel Listener</a></div>
<div class="linkBHEAD"><a href="propertychangelistener.html">How to Write a Property Change Listener</a></div>
<div class="linkBHEAD"><a href="tablemodellistener.html">How to Write a Table Model Listener</a></div>
<div class="linkBHEAD"><a href="treeexpansionlistener.html">How to Write a Tree Expansion Listener</a></div>
<div class="linkBHEAD"><a href="treemodellistener.html">How to Write a Tree Model Listener</a></div>
<div class="linkBHEAD"><a href="treeselectionlistener.html">How to Write a Tree Selection Listener</a></div>
<div class="linkBHEAD"><a href="treewillexpandlistener.html">How to Write a Tree-Will-Expand Listener</a></div>
<div class="linkBHEAD"><a href="undoableeditlistener.html">How to Write an Undoable Edit Listener</a></div>
<div class="linkBHEAD"><a href="windowlistener.html">How to Write Window Listeners</a></div>
<div class="linkAHEAD"><a href="api.html">Listener API Table</a></div>
<div class="linkAHEAD"><a href="problems.html">Solving Common Event-Handling Problems</a></div>
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            <div id=PageTitle>How to Write a Caret Listener</div>
            <blockquote>

Caret events occur when the <em>caret</em> &#151; the cursor
indicating the insertion
point &#151; in a text component moves
or when the selection in a text component changes.
The text component's document can initiate caret events
when it inserts or removes text, for example.

<h4 align=center><font color=red>[PENDING: Image showing sample caret 
    forthcoming.]</font></h4>

You can attach a caret listener to an instance of any
<code>JTextComponent</code> subclass with the
<code>addCaretListener</code> method. 

<blockquote><hr><strong>Note:</strong>&nbsp;An alternate way of detecting caret changes is to attach a
listener directly to the caret object itself rather than to
the text component that manages the caret. 
A caret fires change events (<em>not</em>
caret events), so you would need to write a
<a href="changelistener.html">change listener</a>
rather than a caret listener.
<hr></blockquote>

<p>
Here is the caret event handling code from an application
called <code>TextComponentDemo</code>:

<blockquote><pre>
...
<em>//where initialization occurs</em>
CaretListenerLabel caretListenerLabel =
    new CaretListenerLabel("Caret Status");
...
textPane.addCaretListener(caretListenerLabel);
...
protected class CaretListenerLabel extends JLabel
                                   implements CaretListener
{
    ...
    //Might not be invoked from the event dispatching thread.
    public void caretUpdate(CaretEvent e) {
        displaySelectionInfo(e.getDot(), e.getMark());
    }

    //This method can be invoked from any thread.  It 
    //invokes the setText and modelToView methods, which 
    //must run in the event dispatching thread. We use
    //invokeLater to schedule the code for execution
    //in the event dispatching thread.
    protected void displaySelectionInfo(final int dot,
                                        final int mark) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                if (dot == mark) {  // no selection
                    ...
                }
            });
        }
    }
}
</pre></blockquote>

<blockquote><hr><strong>Note:</strong>&nbsp;The <code>caretUpdate</code> method is not guaranteed
to be called in the event-dispatching thread.
To use any methods inside of <code>caretUpdate</code>
that update the GUI special
handling is required to ensure they are executed on
the event-dispatching thread.  You can do this by wrapping
the code inside a <code>Runnable</code> and calling
<code>SwingUtilities.invokeLater</code> on that
<code>Runnable</code>.
<hr></blockquote>

You can find a link to the source file for
<code>TextComponentDemo</code> in the
<a class="TutorialLink" target="_top" href="../components/examples/index.html#TextComponentDemo">example index for Using Swing Components</a>.  For a discussion about the caret listener aspect
of the program see
<a class="TutorialLink" target="_top" href="../components/generaltext.html#caret">Listening for Caret and Selection Changes</a> in
<a class="TutorialLink" target="_top" href="../components/generaltext.html">Text Component Features</a>.

</blockquote>
<h3>
<a name="api">The Caret Listener API</a>
</h3>
<blockquote>

<p align=center><a name="caretlistener">The CaretListener
   Interface</a>
<p><em>Because <code>CaretListener</code> has only one method,
   it has no corresponding adapter class.</em>
<table border=1>
<tr>
<th align=left>Method</th>
<th align=left>Purpose</th>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/CaretListener.html#caretUpdate(javax.swing.event.CaretEvent)">caretUpdate(CaretEvent)</a></td>
<td>Called when the caret in the listened-to component moves
    or when the selection in the listened-to component changes.
</td>
</tr>
</table>

<p align=center><a name="caretevent">The CaretEvent Class</a>
<p>
<table border=1>
<tr>
<th align=left>Method</th>
<th align=left>Purpose</th>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/CaretEvent.html#getDot()">int getDot()</a></td>
<td>Returns the current location of the caret.
    If text is selected, the caret marks one end of the selection.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/CaretEvent.html#getMark()">int getMark()</a></td>
<td>Returns the other end of the selection.
    If nothing is selected,
    the value returned by this method is equal to the
    value returned by <code>getDot</code>.
    Note that the dot is not guaranteed to be less than the mark.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/util/EventObject.html#getSource()">Object getSource()</a><br>(<em>in <code>java.util.EventObject</code></em>)
</td>
<td>Returns the object that fired the event.
</td>
</tr>
</table>
</blockquote>

<a name="eg">
<h3>Examples that Use Caret Listeners</h3>
</a>
<blockquote>
The following table lists the
examples that use caret listeners.
<p>

<table>
<tr>
<th align=left> Example
</th>
<th align=left> Where Described
</th>
<th align=left> Notes

</th>
</tr>
<tr valign=top>
<td> <a href="../components/examples/index.html#TextComponentDemo"><code>TextComponentDemo</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/generaltext.html#caret">Listening for Caret and Selection Changes</a></td>
<td> Uses a listener label to display caret and selection status.

</td>
</tr>
</table>
        </blockquote>
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