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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="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="nolinkBHEAD">How to Write a Tree Expansion Listener</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 Tree Expansion Listener</div>
            <blockquote>

Sometimes when using a 
<a class="TutorialLink" target="_top" href="../components/tree.html">tree</a>, you might need to react when a branch becomes expanded or collapsed.
For example, you might need to load or save data.
Or you might need to prevent the user
from expanding a particular node.

<p>
Two kinds of listeners report expansion and collapse occurrences:
tree expansion listeners and tree-will-expand listeners.
This page discusses the former.
A tree expansion listener detects when an expansion or collapse
has happened.
In general, you should implement a tree expansion listener
unless you might need to prevent an expansion or collapse
from happening.

<p>
Tree-will-expand listeners are discussed in
<a href="treewillexpandlistener.html">How to Write a Tree-Will-Expand
Listener</a>.
A tree-will-expand listener detects when an expansion or collapse
is about to happen.

<p>
The following example demonstrates a simple tree expansion listener.
The text area at the bottom of the window
displays a message every time a tree expansion event occurs.
It's a straightforward, simple demo.
To see a more interesting version that can veto expansions, see
<a href="treewillexpandlistener.html">How to Write a Tree-Will-Expand
Listener</a>.

<p>

<p><center><IMG SRC="../../figures/uiswing/events/TreeExpandEventDemo.png" WIDTH="412" HEIGHT="195" ALIGN="BOTTOM" ALT=""></center></p>

<blockquote><hr><strong>Try this:</strong>&nbsp;<ol>
<li> <a href="http://java.sun.com/docs/books/tutorialJWS/uiswing/events/examples/TreeExpandEventDemo.jnlp">Run
     TreeExpandEventDemo</a> using
     <a href=http://java.sun.com/products/javawebstart>
     Java<sup><font size=-2>TM</font></sup> Web Start</a>.
     Or, to compile and run the example yourself,
     consult the
     <a href="examples/index.html#TreeExpandEventDemo">example index</a>.
<li> Expand a node.  A tree-expanded event is fired.
<li> Collapse the node.  A tree-collapsed event is fired.
</ol>
<hr></blockquote>

<p>
The following code shows how the program handles expansion events.
You can find all the example's source code in

<a class="SourceLink" target="_blank" href="examples/TreeExpandEventDemo.java"><code>TreeExpandEventDemo.java</code></a>.

<blockquote><pre>
public class TreeExpandEventDemo ... {
    ...
    void saySomething(String eventDescription, TreeExpansionEvent e) {
        textArea.append(eventDescription + "; "
                        + "path = " + e.getPath()
                        + newline);
    }

    class DemoArea ... implements TreeExpansionListener {
        ...
        public DemoArea() {
            ...
            tree.addTreeExpansionListener(this);
            ...
        }
        ...
        // Required by TreeExpansionListener interface.
        public void treeExpanded(TreeExpansionEvent e) {
            saySomething("Tree-expanded event detected", e);
        }

        // Required by TreeExpansionListener interface.
        public void treeCollapsed(TreeExpansionEvent e) {
            saySomething("Tree-collapsed event detected", e);
        }
    }
}
</pre></blockquote>

</blockquote>

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

<p align=center><a name="treeexpansionlistener">The TreeExpansionListener
   Interface</a>
<p><em><code>TreeExpansionListener</code> has no 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/TreeExpansionListener.html#treeCollapsed(javax.swing.event.TreeExpansionEvent)">treeCollapsed(TreeExpansionEvent)</a></td>
<td> Called just after a tree node collapses.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeExpansionListener.html#treeExpanded(javax.swing.event.TreeExpansionEvent)">treeExpanded(TreeExpansionEvent)</a></td>
<td> Called just after a tree node expands.
</td>
</tr>
</table>

<p align=center><a name="treeexpansionevent">The TreeExpansionEvent API</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></td>
<td>Return the object that fired the event.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeExpansionEvent.html#getPath()">TreePath getPath()</a></td>
<td>Returns a 
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/tree/TreePath.html"><code>TreePath</code></a> object that identifies each node from the root of the tree
 to the collapsed/expanded node, inclusive.
</td>
</tr>
</table>

</blockquote>
<a name="eg">
<h3>Examples that Use Tree Expansion Listeners</h3>
</a>
<blockquote>
The following table lists the
examples that use tree expansion 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="examples/index.html#TreeExpandEventDemo">
     <code>TreeExpandEventDemo</code></a>
</td>
<td> This section
</td>
<td> Displays a message whenever a tree expansion event occurs.

</td>
</tr>
<tr valign=top>
<td> <a href="examples/index.html#TreeExpandEventDemo2">
     <code>TreeExpandEventDemo2</code></a>
</td>
<td> <a href="treewillexpandlistener.html">How to Write a 
     Tree-Will-Expand Listener</a>
</td>
<td> Adds a tree-will-expand listener to <code>TreeExpandEventDemo</code>.

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