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HTML
216 lines
7.7 KiB
HTML
<?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>Retrieving Database Items</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="BasicProgram.html" title="Chapter 2. The Basic Program" />
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<link rel="prev" href="addingdatabaseitems.html" title="Adding Database Items" />
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<link rel="next" href="handlingexceptions.html" title="Handling Exceptions" />
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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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Retrieving Database Items
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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="addingdatabaseitems.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The Basic Program
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="handlingexceptions.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="retrievingdatabaseitems"></a>
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Retrieving Database Items
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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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Retrieving information from the database is accomplished via the
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standard Java collections API. In the example, the
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Set.html#iterator()" target="_top">Set.iterator</a>
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method is used to iterate all
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.Entry.html" target="_top">Map.Entry</a>
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objects for each store. All standard Java methods for retrieving
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objects from a collection may be used with the JE JE Collections API.
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</p>
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<p>
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The <code class="methodname">PrintDatabase.doWork()</code> method calls
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<code class="methodname">printEntries()</code>
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to print the map entries for each database store. It is called via
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the
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<a class="ulink" href="../../java/com/sleepycat/collections/TransactionRunner.html" target="_top">TransactionRunner</a>
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class and was outlined in the previous section.
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</p>
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<a id="cb_printdatabase"></a>
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<pre class="programlisting">import java.util.Iterator;
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...
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public class Sample
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{
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...
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private SampleViews views;
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...
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private class PrintDatabase implements TransactionWorker
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{
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public void doWork()
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throws Exception
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{
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<strong class="userinput"><code> printEntries("Parts",
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views.getPartEntrySet().iterator());
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printEntries("Suppliers",
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views.getSupplierEntrySet().iterator());
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printEntries("Shipments",
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views.getShipmentEntrySet().iterator());</code></strong>
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}
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}
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...
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<strong class="userinput"><code> private void printEntries(String label, Iterator iterator)
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{
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}</code></strong>
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...
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} </pre>
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<p>
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The
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Set.html" target="_top">Set</a>
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of
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.Entry.html" target="_top">Map.Entry</a>
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objects for each store is obtained from the <code class="classname">SampleViews</code>
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object. This set can also be obtained by calling the
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.html#entrySet()" target="_top">Map.entrySet</a>
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method of a stored map.
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</p>
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<p>
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The <code class="methodname">printEntries()</code> prints the map entries for any stored
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map. The
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/Object.html#toString()" target="_top">Object.toString</a>
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method of each key and value is called to
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obtain a printable representation of each object.
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</p>
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<a id="cb_printentries"></a>
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<pre class="programlisting"> private void printEntries(String label, Iterator iterator)
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{
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<strong class="userinput"><code> System.out.println("\n--- " + label + " ---");
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while (iterator.hasNext())
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{
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Map.Entry entry = (Map.Entry) iterator.next();
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System.out.println(entry.getKey().toString());
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System.out.println(entry.getValue().toString());
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}</code></strong>
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} </pre>
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<p>
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This is one of a small number of behavioral differences between
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standard Java collections and stored collections. For a complete
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list see
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<a class="xref" href="UsingStoredCollections.html" title="Using Stored Collections">
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Using Stored Collections
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</a>.
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</p>
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<p>
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The output of the example program is shown below.
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</p>
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<pre class="programlisting">Adding Suppliers
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Adding Parts
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Adding Shipments
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--- Parts ---
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PartKey: number=P1
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PartData: name=Nut color=Red weight=[12.0 grams] city=London
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PartKey: number=P2
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PartData: name=Bolt color=Green weight=[17.0 grams] city=Paris
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PartKey: number=P3
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PartData: name=Screw color=Blue weight=[17.0 grams] city=Rome
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PartKey: number=P4
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PartData: name=Screw color=Red weight=[14.0 grams] city=London
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PartKey: number=P5
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PartData: name=Cam color=Blue weight=[12.0 grams] city=Paris
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PartKey: number=P6
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PartData: name=Cog color=Red weight=[19.0 grams] city=London
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--- Suppliers ---
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SupplierKey: number=S1
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SupplierData: name=Smith status=20 city=London
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SupplierKey: number=S2
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SupplierData: name=Jones status=10 city=Paris
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SupplierKey: number=S3
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SupplierData: name=Blake status=30 city=Paris
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SupplierKey: number=S4
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SupplierData: name=Clark status=20 city=London
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SupplierKey: number=S5
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SupplierData: name=Adams status=30 city=Athens
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--- Shipments ---
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ShipmentKey: supplier=S1 part=P1
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ShipmentData: quantity=300
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ShipmentKey: supplier=S2 part=P1
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ShipmentData: quantity=300
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ShipmentKey: supplier=S1 part=P2
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ShipmentData: quantity=200
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ShipmentKey: supplier=S2 part=P2
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ShipmentData: quantity=400
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ShipmentKey: supplier=S3 part=P2
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ShipmentData: quantity=200
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ShipmentKey: supplier=S4 part=P2
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ShipmentData: quantity=200
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ShipmentKey: supplier=S1 part=P3
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ShipmentData: quantity=400
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ShipmentKey: supplier=S1 part=P4
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ShipmentData: quantity=200
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ShipmentKey: supplier=S4 part=P4
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ShipmentData: quantity=300
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ShipmentKey: supplier=S1 part=P5
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ShipmentData: quantity=100
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ShipmentKey: supplier=S4 part=P5
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ShipmentData: quantity=400
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ShipmentKey: supplier=S1 part=P6
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ShipmentData: quantity=100 </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="addingdatabaseitems.html">Prev</a> </td>
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||
<td width="20%" align="center">
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<a accesskey="u" href="BasicProgram.html">Up</a>
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||
</td>
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||
<td width="40%" align="right"> <a accesskey="n" href="handlingexceptions.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">
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Adding Database Items
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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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Handling Exceptions
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</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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