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254 lines
9.1 KiB
HTML
254 lines
9.1 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>Implementing the Main Program</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="createbindingscollections.html" title="Creating Bindings and Collections" />
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<link rel="next" href="usingtransactions.html" title="Using Transactions" />
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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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Implementing the Main Program
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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="createbindingscollections.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="usingtransactions.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="implementingmain"></a>
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Implementing the Main Program
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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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The main program opens the environment and databases, stores and retrieves
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objects within a transaction, and finally closes the environment
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databases. This section describes the main program shell, and the
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next section describes how to run transactions for storing and
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retrieving objects.
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</p>
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<p>
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The <code class="classname">Sample</code> class contains the main program. The skeleton
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for the <code class="classname">Sample</code> class follows.
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</p>
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<a id="cb_je_sample"></a>
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<pre class="programlisting"><strong class="userinput"><code>import com.sleepycat.je.DatabaseException;
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import java.io.FileNotFoundException;
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public class Sample
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{
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private SampleDatabase db;
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private SampleViews views;
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public static void main(String args)
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{
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}
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private Sample(String homeDir)
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throws DatabaseException, FileNotFoundException
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{
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}
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private void close()
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throws DatabaseException
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{
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}
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private void run()
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throws Exception
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{
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}
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}</code></strong> </pre>
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<p>
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The main program uses the <code class="classname">SampleDatabase</code> and
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<code class="classname">SampleViews</code> classes that were described in the preceding
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sections. The <code class="methodname">main</code> method will create an instance of the
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<code class="classname">Sample</code> class, and call its <code class="methodname">run()</code> and <code class="methodname">close()</code>
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methods.
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</p>
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<p>
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The following statements parse the program's command line
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arguments.
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</p>
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<a id="cb_main"></a>
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<pre class="programlisting"> public static void main(String[] args)
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{
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<strong class="userinput"><code> System.out.println("\nRunning sample: " + Sample.class);
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String homeDir = "./tmp";
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for (int i = 0; i < args.length; i += 1)
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{
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String arg = args[i];
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if (args[i].equals("-h") && i < args.length - 1)
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{
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i += 1;
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homeDir = args[i];
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}
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else
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{
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System.err.println("Usage:\n java " +
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Sample.class.getName() +
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"\n [-h <home-directory>]");
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System.exit(2);
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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 usage command is:
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</p>
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<pre class="programlisting"><strong class="userinput"><code>java com.sleepycat.examples.bdb.shipment.basic.Sample
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[-h <home-directory> ]</code></strong> </pre>
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<p>
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The <code class="literal">-h</code> command is used to set the <code class="filename">homeDir</code>
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variable, which will later be passed to the <code class="methodname">SampleDatabase()</code>
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constructor. Normally all Berkeley DB programs should provide a way
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to configure their database environment home directory.
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</p>
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<p>
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The default for the home directory is <code class="filename">./tmp</code> — the tmp
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subdirectory of the current directory where the sample is run. The
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home directory must exist before running the sample. To re-create
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the sample database from scratch, delete all files in the home
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directory before running the sample.
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</p>
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<p>
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The home directory was described previously in
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<a class="xref" href="opendbenvironment.html" title="Opening and Closing the Database Environment">
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Opening and Closing the Database Environment
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</a>.
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</p>
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<p>
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Of course, the command line arguments shown are only examples
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and a real-life application may use different techniques for
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configuring these options.
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</p>
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<p>
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The following statements create an instance of the <code class="classname">Sample</code>
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class and call its <code class="methodname">run()</code> and <code class="methodname">close()</code> methods.
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</p>
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<a id="cb_main2"></a>
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<pre class="programlisting"> public static void main(String args)
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{
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...
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<strong class="userinput"><code> Sample sample = null;
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try
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{
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sample = new Sample(homeDir);
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sample.run();
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}
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catch (Exception e)
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{
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e.printStackTrace();
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}
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finally
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{
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if (sample != null)
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{
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try
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{
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sample.close();
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}
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catch (Exception e)
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{
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System.err.println("Exception during database close:");
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e.printStackTrace();
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}
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}
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}</code></strong>
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} </pre>
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<p>
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The <code class="methodname">Sample()</code> constructor will open the environment and
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databases, and the <code class="methodname">run()</code> method will run transactions for
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storing and retrieving objects. If either of these throws an
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exception, then the program was unable to run and should normally
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terminate. (Transaction retries are handled at a lower level and
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will be described later.) The first <code class="literal">catch</code> statement handles
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such exceptions.
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</p>
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<p>
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The <code class="literal">finally</code> statement is used to call the <code class="methodname">close()</code>
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method since an attempt should always be made to close the environment and
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databases
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cleanly. If an exception is thrown during close and a prior
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exception occurred above, then the exception during close is likely
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a side effect of the prior exception.
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</p>
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<p>
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The <code class="methodname">Sample()</code> constructor creates the <code class="literal">SampleDatabase</code>
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and <code class="classname">SampleViews</code> objects.
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</p>
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<a id="cb_sample"></a>
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<pre class="programlisting"> private Sample(String homeDir)
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throws DatabaseException, FileNotFoundException
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{
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<strong class="userinput"><code> db = new SampleDatabase(homeDir);
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views = new SampleViews(db);</code></strong>
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} </pre>
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<p>
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Recall that creating the <code class="classname">SampleDatabase</code> object will open
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the environment and all databases.
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</p>
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<p>
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To close the database the <code class="methodname">Sample.close()</code> method simply
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calls <code class="methodname">SampleDatabase.close()</code>.
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</p>
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<a id="cb_sample-close"></a>
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<pre class="programlisting"> private void close()
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throws DatabaseException
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{
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<strong class="userinput"><code> db.close();</code></strong>
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} </pre>
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<p>
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The <code class="methodname">run()</code> method is described in the next section.
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</p>
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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>
|
||
<td width="40%" align="left"><a accesskey="p" href="createbindingscollections.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="usingtransactions.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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Creating Bindings and Collections
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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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Using Transactions
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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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