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8.2 KiB
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Using Tuples with Key Creators</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Java Edition Collections Tutorial" />
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<link rel="up" href="Tuple.html" title="Chapter 5. Using Tuples" />
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<link rel="prev" href="Tuple.html" title="Chapter 5. Using Tuples" />
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<link rel="next" href="tuplekeybindings.html" title="Creating Tuple Key Bindings" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">
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Using Tuples with Key Creators
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</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="Tuple.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5.
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Using Tuples
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="tuplekeybindings.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="tupleswithkeycreators"></a>
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Using Tuples with Key Creators
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</h2>
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</div>
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</div>
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</div>
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<p>
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Key creators were used in prior examples to extract index keys
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from value objects. The keys were returned as deserialized key
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objects, since the serial format was used for keys. In this
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example, the tuple format is used for keys and the key creators
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return keys by writing information to a tuple. The differences
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between this example and the prior example are:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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The
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/TupleSerialKeyCreator.html" target="_top">TupleSerialKeyCreator</a>
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base class is used instead of the
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialSerialKeyCreator.html" target="_top">SerialSerialKeyCreator</a>
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base class.
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</p>
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</li>
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<li>
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<p>
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For all key input and output parameters, the
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleInput.html" target="_top">TupleInput</a>
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and
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleOutput.html" target="_top">TupleOutput</a>
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classes are used instead of
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/Object.html" target="_top">Object</a>
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(representing a deserialized object).
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</p>
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</li>
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<li>
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<p>
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Instead of returning a key output object, these methods call
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tuple write methods such as
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleOutput.html#writeString(java.lang.String)" target="_top">TupleOutput.writeString</a>.
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</p>
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</li>
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</ul>
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</div>
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<p>
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In addition to writing key tuples, the
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<code class="classname">ShipmentByPartKeyCreator</code> and
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<code class="classname">ShipmentBySupplierKeyCreator</code> classes also read the key tuple
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of the primary key. This is because they extract the index key from
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fields in the Shipment's primary key. Instead of calling getter
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methods on the <code class="classname">ShipmentKey</code> object, as in prior examples,
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these methods call
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleInput.html#readString()" target="_top">TupleInput.readString</a>.
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The <code class="classname">ShipmentKey</code> consists of two string fields that are read
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in sequence.
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</p>
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<p>
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The modified key creators are shown below:
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<code class="classname">SupplierByCityKeyCreator</code>,
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<code class="classname">ShipmentByPartKeyCreator</code>
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and <code class="classname">ShipmentBySupplierKeyCreator</code>.
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</p>
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<a id="tuple_SupplierByCityKeyCreator"></a>
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<pre class="programlisting"><strong class="userinput"><code>import com.sleepycat.bind.serial.TupleSerialKeyCreator;
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import com.sleepycat.bind.tuple.TupleInput;
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import com.sleepycat.bind.tuple.TupleOutput;
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...</code></strong>
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public class SampleDatabase
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{
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...
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private static class SupplierByCityKeyCreator
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<strong class="userinput"><code> extends TupleSerialKeyCreator</code></strong>
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{
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private SupplierByCityKeyCreator(ClassCatalog catalog,
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<strong class="userinput"><code>Class valueClass</code></strong>)
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{
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super(catalog, valueClass);
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}
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<strong class="userinput"><code> public boolean createSecondaryKey(TupleInput primaryKeyInput,
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Object valueInput,
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TupleOutput indexKeyOutput)
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{
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SupplierData supplierData = (SupplierData) valueInput;
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String city = supplierData.getCity();
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if (city != null) {
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indexKeyOutput.writeString(supplierData.getCity());
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return true;
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} else {
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return false;
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}
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}</code></strong>
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}
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private static class ShipmentByPartKeyCreator
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<strong class="userinput"><code>extends TupleSerialKeyCreator</code></strong>
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{
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private ShipmentByPartKeyCreator(ClassCatalog catalog,
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<strong class="userinput"><code>Class valueClass</code></strong>)
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{
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super(catalog, valueClass);
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}
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<strong class="userinput"><code>public boolean createSecondaryKey(TupleInput primaryKeyInput,
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Object valueInput,
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TupleOutput indexKeyOutput)
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{
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String partNumber = primaryKeyInput.readString();
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// don't bother reading the supplierNumber
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indexKeyOutput.writeString(partNumber);
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return true;
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}</code></strong>
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}
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private static class ShipmentBySupplierKeyCreator
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<strong class="userinput"><code>extends TupleSerialKeyCreator</code></strong>
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{
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private ShipmentBySupplierKeyCreator(ClassCatalog catalog,
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<strong class="userinput"><code>Class valueClass</code></strong>)
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{
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super(catalog, valueClass);
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}
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<strong class="userinput"><code>public boolean createSecondaryKey(TupleInput primaryKeyInput,
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Object valueInput,
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TupleOutput indexKeyOutput)
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{
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primaryKeyInput.readString(); // skip the partNumber
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String supplierNumber = primaryKeyInput.readString();
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indexKeyOutput.writeString(supplierNumber);
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return true;
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}</code></strong>
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}
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...
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}
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</pre>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="Tuple.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="Tuple.html">Up</a>
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</td>
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|
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<td width="40%" align="right"> <a accesskey="n" href="tuplekeybindings.html">Next</a></td>
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|
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</tr>
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|
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<tr>
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|
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<td width="40%" align="left" valign="top">Chapter 5.
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|||
|
|
Using Tuples
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|||
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</td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top">
|
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|
|
Creating Tuple Key Bindings
|
|||
|
|
</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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