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112 lines
6.7 KiB
HTML
112 lines
6.7 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>Java programming notes</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 Programmer's Reference Guide" />
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<link rel="up" href="java.html" title="Chapter 5. Java API" />
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<link rel="prev" href="java_compat.html" title="Compatibility" />
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<link rel="next" href="java_faq.html" title="Java FAQ" />
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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 11.2.5.3</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">Java programming notes</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="java_compat.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5.
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Java API
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="java_faq.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="java_program"></a>Java programming notes</h2>
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</div>
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</div>
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</div>
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<p>Although the Java API parallels the Berkeley DB C++/C interface in many ways,
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it differs where the Java language requires. For example, the handle
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method names are camel-cased and conform to Java naming patterns. (The
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C++/C method names are currently provided, but are deprecated.)</p>
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<div class="orderedlist">
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<ol type="1">
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<li>The Java runtime does not automatically close Berkeley DB objects on
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finalization. There are several reasons for this. One is that
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finalization is generally run only when garbage collection occurs, and
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there is no guarantee that this occurs at all, even on exit. Allowing
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specific Berkeley DB actions to occur in ways that cannot be replicated seems
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wrong. Second, finalization of objects may happen in an arbitrary
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order, so we would have to do extra bookkeeping to make sure that
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everything was closed in the proper order. The best word of advice is
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to always do a close() for any matching open() call. Specifically, the
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Berkeley DB package requires that you explicitly call close on each individual
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<a class="ulink" href="../java/com/sleepycat/db/Database.html" target="_top">Database</a> and
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<a class="ulink" href="../java/com/sleepycat/db/Cursor.html" target="_top">Cursor</a> object that you opened. Your database
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activity may not be synchronized to disk unless you do so.</li>
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<li>Some methods in the Java API have no return type, and throw a
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<a class="ulink" href="../java/com/sleepycat/db/DatabaseException.html" target="_top">DatabaseException</a> when an severe error
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arises. There are some notable methods that do have a return value, and
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can also throw an exception. The "get" methods in
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<a class="ulink" href="../java/com/sleepycat/db/Database.html" target="_top">Database</a> and
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<a class="ulink" href="../java/com/sleepycat/db/Cursor.html" target="_top">Cursor</a> both return 0 when a get
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succeeds, <a class="link" href="program_errorret.html#program_errorret.DB_NOTFOUND">DB_NOTFOUND</a> when the key is not found, and throw an
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error when there is a severe error. This approach allows the programmer
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to check for typical data-driven errors by watching return values
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without special casing exceptions.
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<p>An object of type <a class="ulink" href="../java/com/sleepycat/db/MemoryException.html" target="_top">MemoryException</a> is
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thrown when a Dbt is too small to hold the corresponding key or data item.</p><p>An object of type <a class="ulink" href="../java/com/sleepycat/db/DeadlockException.html" target="_top">DeadlockException</a> is
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thrown when a deadlock would occur.</p><p>An object of type <a class="ulink" href="../java/com/sleepycat/db/RunRecoveryException.html" target="_top">RunRecoveryException</a>, a
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subclass of <a class="ulink" href="../java/com/sleepycat/db/DatabaseException.html" target="_top">DatabaseException</a>, is thrown when
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there is an error that requires a recovery of the database using <a href="../api_reference/C/db_recover.html" class="olink">db_recover</a> utility.</p><p>An object of type <a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/IllegalArgumentException.html" target="_top">IllegalArgumentException</a>
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a standard Java Language exception, is thrown when there is an error in
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method arguments.</p><p>An object of type <a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/OutOfMemoryError.html" target="_top">OutOfMemoryError</a> is thrown
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when the system cannot provide enough memory to complete the operation
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(the ENOMEM system error on UNIX).</p></li>
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<li>If there are embedded nulls in the <span class="bold"><strong>curslist</strong></span> argument for
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<a class="ulink" href="../java/com/sleepycat/db/Database.html#join(com.sleepycat.db.Cursor[], com.sleepycat.db.JoinConfig)" target="_top">Database.join(com.sleepycat.db.Cursor[], com.sleepycat.db.JoinConfig)</a>,
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they will be treated as the end of the list of cursors, even if you
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may have allocated a longer array. Fill in all the cursors in your
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array unless you intend to cut it short.</li>
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<li>If you are using custom class loaders in your application, make sure
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that the Berkeley DB classes are loaded by the system class loader, not a
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custom class loader. This is due to a JVM bug that can cause an access
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violation during finalization (see the bug 4238486 in Sun Microsystem's
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Java Bug Database).</li>
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</ol>
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</div>
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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="java_compat.html">Prev</a> </td>
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||
<td width="20%" align="center">
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||
<a accesskey="u" href="java.html">Up</a>
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||
</td>
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<td width="40%" align="right"> <a accesskey="n" href="java_faq.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">Compatibility </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"> Java FAQ</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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