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<TITLE>Finding a Preference in a Preference Tree (Java Developers Almanac Example)
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<h1>The Java Developers Almanac 1.4</h1>
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<A HREF="../index.html">List of Packages</A>
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<A HREF="../java.util.prefs/pkg.html">java.util.prefs</A><font color="#666666" class="xsmall-font">
[18 examples]
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<B><A HREF="../java.util.prefs/pkg.html#Nodes">Nodes</A></B><font color="#666666" class="xsmall-font">
[7 examples]
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<h3>e417. Finding a Preference in a Preference Tree</h3>
There is no efficient method for finding a key in a preference node.
All the nodes must be traversed and checked for the presence of the
key. This example implements such a method.
<P> This example can be modified to find nodes that matched values
rather than keys by replacing <code>contains()</code> with
<code>containsValue()</code>, as defined in
<a href="../java.util.prefs/ContainsValue.html" class="eglink"><b>e407</b> Determining If a Preference Node Contains a Specific Value</a>.
<pre> // Find first occurrence
Preferences prefs = findNode(Preferences.userRoot(), null, <font color="#0066ff"><i>"key"</i></font>);
// Find all occurrences
prefs = findNode(Preferences.userRoot(), null, <font color="#0066ff"><i>"key"</i></font>);
while (prefs != null) {
prefs = findNode(Preferences.userRoot(), prefs, "key");
}
// Traverses all the nodes from root depth-first.
// Returns the first node that contains the specified key.
// If start is non-null, the nodes are checked only after the
// start node is encountered.
// Returns null if not found.
public static Preferences findNode(Preferences root, Preferences start, String key) {
// For the implementation of contains,
// see <a href="../java.util.prefs/Contains.html" class="eglink"><b>e406</b> Determining If a Preference Node Contains a Specific Key</a>
if (start == null && contains(root, key)) {
// Found the key
return root;
}
// The start node has been encountered so start checking from now on
if (start != null && root.equals(start)) {
start = null;
}
// Recursively check the child nodes
try {
String[] names = root.childrenNames();
for (int i=0; i<names.length; i++) {
Preferences n = findNode(root.node(names[i]), start, key);
if (n != null) {
// Found the key
return n;
}
}
} catch (BackingStoreException e) {
}
// Not found
return null;
}
</pre>
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<b>Related Examples</b></font></td>
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e411. <a class="eglink" href="GetRoot.html?l=rel">
Getting the Roots of the Preference Trees
</a>
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e412. <a class="eglink" href="CreateNode.html?l=rel">
Creating a Preference Node
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e413. <a class="eglink" href="GetNode.html?l=rel">
Retrieving a Preference Node
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e414. <a class="eglink" href="RemNode.html?l=rel">
Removing a Preference Node
</a>
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e415. <a class="eglink" href="NodeExists.html?l=rel">
Determining If a Preference Node Exists
</a>
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e416. <a class="eglink" href="GetRelative.html?l=rel">
Retrieving the Parent and Child Nodes of a Preference Node
</a>
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See also:
<a class="eglink" href="/egs/java.util.prefs/pkg.html?l=rel#Events">
Events
</a>
<a class="eglink" href="/egs/java.util.prefs/pkg.html?l=rel#Importing%20and%20Exporting">
Importing and Exporting
</a>
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