<?xml version="1.0" encoding="UTF-8"?>
<books>
    <book id="12">
        <name>think in java</name>
        <price>85.5</price>
        <author>Edwrad Saverin</author>
    </book>
    <book id="15">
        <name>Spring in Action</name>
        <price>39.0</price>
        <author>Edward Saverin</author>    
    </book>
</books>

NodeList bookNodes=element.getElementsByTagName("book");
        for(int i=0;i<bookNodes.getLength();i++){
            Element bookElement=(Element)bookNodes.item(i);
            Book book=new Book();
            book.setId(Integer.parseInt(bookElement.getAttribute("id")));
            NodeList childNodes=bookElement.getChildNodes();
            System.out.println("childnodes："+childNodes.getLength());

为什么childnodes的长度为7？