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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>有關(guān)代碼的說明</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 4 頁（共7 頁）</nobr></font></td>
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<p>您應(yīng)該注意前一頁代碼中創(chuàng)建子類的使用。在 <code>ManagerImpl</code> 類聲明中，請注意附加標(biāo)記屬性 <code>persistence-capable-superclass</code>，它標(biāo)識了也具有持久性能力的超類。集合的標(biāo)識也非常有趣。有關(guān)集合的附加信息包含在 <code>DepartmentImpl</code> 的 <code>employees</code> 字段聲明中（請回憶 <code>employees</code> 屬于類型 <code>Collection</code>）。<code>element-type</code> 屬性標(biāo)識包含在常規(guī)集合內(nèi)的類的類型。</p>
<p>本教程中我們簡單地查看了元數(shù)據(jù)，只顯示啟動和運行所需的屬性。在 JDO 規(guī)范中，您會找到標(biāo)題為&ldquo;XML Metadata&rdquo;的一節(jié)；請閱讀此節(jié)以了解有關(guān)控制應(yīng)用程序中數(shù)據(jù)的更多信息。</p>
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