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        <br><b>Lesson:</b> Writing Event Listeners
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<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="nolinkBHEAD">How to Write a Tree Selection Listener</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 Selection Listener</div>
            <blockquote>

To detect when the user selects a node in a
<a class="TutorialLink" target="_top" href="../components/tree.html">tree</a>, you need to register a tree selection listener.
Here is an example, taken from 
the <code>TreeDemo</code> example discussed in
<a class="TutorialLink" target="_top" href="../components/tree.html#select">Responding to Node Selection</a>, of detecting node selection
in a tree that can have at most one node 
selected at a time:

<p><font color=red>
[PENDING: Update this code snippet after example has been
modified to remove the inner class.]</font>

<blockquote><pre>
tree.addTreeSelectionListener(new TreeSelectionListener() {
    public void valueChanged(TreeSelectionEvent e) {
        DefaultMutableTreeNode node = (DefaultMutableTreeNode)
                           tree.getLastSelectedPathComponent();

        if (node == null) return;

        Object nodeInfo = node.getUserObject();
	...
        <em>/* React to the node selection. */</em>
	...
    }
});
</pre></blockquote>

To specify that the tree should support single selection,
the program uses this code:

<blockquote><pre>
tree.getSelectionModel().setSelectionMode
        (TreeSelectionModel.SINGLE_TREE_SELECTION);
</pre></blockquote>

The <code>TreeSelectionModel</code> interface
defines three values for the selection mode:

<dl>
<dt> <b><code>DISCONTIGUOUS_TREE_SELECTION</code></b>
<dd> This is the default mode for the default tree selection model.
     With this mode, any combination of nodes can be selected.
<dt> <b><code>SINGLE_TREE_SELECTION</code></b>
<dd> This is the mode used by the preceding example.
     At most one node can be selected at a time.
<dt> <b><code>CONTIGUOUS_TREE_SELECTION</code></b>
<dd> With this mode, only nodes in adjoining rows can be selected.
</dl>


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

<p align=center><a name="treeselectionlistener">The TreeSelectionListener
   Interface</a>
<p><em>Because <code>TreeSelectionListener</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/TreeSelectionListener.html#valueChanged(javax.swing.event.TreeSelectionEvent)">valueChanged(TreeSelectionEvent)</a></td>
<td> Called whenever the selection changes.
</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><br>(<em>in <code>java.util.EventObject</code></em>)
</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/TreeSelectionEvent.html#getNewLeadSelectionPath()">TreePath getNewLeadSelectionPath()</a></td>
<td> Return the current lead path.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeSelectionEvent.html#getOldLeadSelectionPath()">TreePath getOldLeadSelectionPath()</a></td>
<td> Return the path that was previously the lead path.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeSelectionEvent.html#getPath()">TreePath getPath()</a></td>
<td> Return the first path element.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeSelectionEvent.html#getPaths()">TreePath[] getPaths()</a></td>
<td> Return the paths that have been added or removed from the selection.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeSelectionEvent.html#isAddedPath()">boolean isAddedPath()</a></td>
<td> Return true if the first path element has been added
     to the selection.  Returns false if the first path has
     been removed from the selection.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeSelectionEvent.html#isAddedPath(int)">boolean isAddedPath(int)</a></td>
<td> Return true if the path specified by the index was added to
     the selection.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/event/TreeSelectionEvent.html#isAddedPath(javax.swing.tree.TreePath)">boolean isAddedPath(TreePath)</a></td>
<td> Return true if the specified path was added to the selection.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JTree.html#getLastSelectedPathComponent()">Object getLastSelectedPathComponent()</a></td>
<td> Return the last path component in the first node of
     the current selection.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JTree.html#getLeadSelectionPath()">TreePath getLeadSelectionPath()</a><br>(<em>in <code>JTree</code></em>)
</td>
<td> Return the current lead path.
</td>
</tr>
</table>

</blockquote>

<a name="eg">
<h3>Examples that Use Tree Selection Listeners</h3>
</a>
<blockquote>

The following table lists the
examples that use tree selection 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#TreeDemo"><code>TreeDemo</code></a>
<br>
<font color=red>[PENDING: When this example has been updated
to 1.4, this link will point to it.]</font>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/tree.html">How to Use Trees</a></td>
<td> The tree listener responds to node clicks
     by showing the appropriate HTML document.
</td>
</tr>
</table>
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