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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="linkBHEAD"><a href="caretlistener.html">How to Write a Caret Listener</a></div>
<div class="nolinkBHEAD">How to Write a Change Listener</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 Change Listener</div>
            <blockquote>
A change listener is similar to a 
<a href=propertychangelistener.html>property change listener</a>.
A change listener is registered on an object &#151; typically
a component, but it could be another object, like a model &#151;
and the listener is notified when the object has changed.
The big difference from a property change listener is that a
change listener is not notified of <em>what</em> has changed,
but simply that the source object <em>has</em> changed. 
Therefore, a change listener is most useful when
it is only necessary to know when an object has changed in any way.

<p>
Three Swing components rely on change events for basic functionality 
&#151; sliders, color choosers and spinners.
To learn when the value in a
<a class="TutorialLink" target="_top" href="../components/slider.html">slider</a> changes,
you need to register a change listener.
Similarly, you need to register a change listener on a 
<a class="TutorialLink" target="_top" href="../components/colorchooser.html">color chooser</a> to be informed when the user chooses a new color.
You register a change listener on a
<a class="TutorialLink" target="_top" href="../components/spinner.html">spinner</a>, a component introduced in release 1.4,
 to be notified when the spinner's value changes.

<p>

Here is an example of change event handling code for a slider:
 
<blockquote><pre>
<em>//...where initialization occurs:</em>
framesPerSecond.addChangeListener(new SliderListener());
...
class SliderListener implements ChangeListener {
    public void stateChanged(ChangeEvent e) {
        JSlider source = (JSlider)e.getSource();
        if (!source.getValueIsAdjusting()) {
            int fps = (int)source.getValue();
	    ...
        }    
    }
}
</pre></blockquote>

You can find the source file for <code>SliderDemo</code> in the
<a class="TutorialLink" target="_top" href="../components/examples/index.html#SliderDemo">example index for Using Swing Components</a>.

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

<p align=center><a name="changelistener">The ChangeListener
   Interface</a>
<p><em>Because <code>ChangeListener</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/ChangeListener.html#stateChanged(javax.swing.event.ChangeEvent)">stateChanged(ChangeEvent)</a></td>
<td>Called when the listened-to component changes state.
</td>
</tr>
</table>

<p align=center><a name="changeevent">The ChangeEvent 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/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 Change Listeners</h3>
</a>
<blockquote>
The following table lists the
examples that use change 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#SliderDemo">
     <code>SliderDemo</code></a> and
     <br>
     <a href="../components/examples/index.html#SliderDemo2">
     <code>SliderDemo2</code></a>
     <br>
     <a href="../components/examples/index.html#SliderDemo3">
     <code>SliderDemo3</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/slider.html">How to Use Sliders</a></td>
<td> Registers a change listener on a slider that
     controls animation speed.
     The change listener ignores the change events
     until the user releases the slider.

</td>
</tr>
<tr valign=top>
<td> <a href="../components/examples/index.html#ColorChooserDemo">
     <code>ColorChooserDemo</code></a> and
     <br>
     <a href="../components/examples/index.html#ColorChooserDemo2">
     <code>ColorChooserDemo2</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/colorchooser.html  ">How to Use Color Choosers</a></td>
<td> Uses a change listener on the selection model
     of a color chooser to learn when the user changes the current color.

</td>
</tr>

<tr valign=top>
<td> <a href="../components/examples/index.html#SpinnerDemo3">
     <code>SpinnerDemo3</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/spinner.html#change">Detecting Spinner Value Changes</a> in
<a class="TutorialLink" target="_top" href="../components/spinner.html">How to Use Spinners</a>.
</td>
<td> Uses a change listener on a date-field spinner to change
     the color of the text as the spinner's date changes.
</td>
</tr>

<tr valign=top>
<td> <a href="../components/examples/index.html#SpinnerDemo4">
     <code>SpinnerDemo4</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/spinner.html#change">Detecting Spinner Value Changes</a> in
<a class="TutorialLink" target="_top" href="../components/spinner.html">How to Use Spinners</a>.
</td>
<td> Uses a change listener on a spinner to cycle through
     the gray scale as the spinner's value changes.
</td>
</tr>

<tr valign=top>
<td> 
<a class="SourceLink" target="_blank" href="../components/examples/ConverterRangeModel.java"><code>ConverterRangeModel</code></a><br>
     and its subclass,
     <br>
<a class="SourceLink" target="_blank" href="../components/examples/FollowerRangeModel.java"><code>FollowerRangeModel</code></a></td>
<td>
<a class="TutorialLink" target="_top" href="../components/model.html">Using Models</a></td>
<td> Implement custom models for the sliders used
     in the 
     <a href="../components/examples/index.html#Converter">
     <code>Converter</code></a> demo.
     Both models explicitly fire change events when necessary.
</td>
</tr>
</table>



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