Node and Other Generic Interfaces (XML in a Nutshell, 2nd Edition)

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18.3. Node and Other Generic Interfaces

The Node interface is the DOM Core class hierarchy's root. Though never instantiated directly, it is the root interface of all specific interfaces, and you can use it to extract information from any DOM object without knowing its actual type. It is possible to access a document's complete structure and content using only the methods and properties exposed by the Node interface. As shown in Table 18-1, this interface contains information about the type, location, name, and value of the corresponding underlying document data.

Table 18-1. Node interface

Type		Name	Read-only	DOM 2.0
Attributes
DOMString		nodeName
DOMString		nodeValue
Short		Unsigned type
Node		parentNode
NodeList		childNodes
Node		firstChild
Node		lastChild
Node		previousSibling
Node		nextSibling
NamedNodeMap		attributes
Document		ownerDocument
DOMString		namespaceURI
DOMString		Prefix
DOMString		localName
Methods
Boolean		hasAttributes
Node		insertBefore
	Node	newChild
	Node	refChild
Node		replaceChild
	Node	newChild
	Node	oldChild
Node		removeChild
	Node	oldChild
Node		appendChild
	Node	newChild
Boolean		hasChildNodes
Node		cloneNode
	Boolean	Deep
Void		normalize
Boolean		isSupported
	DOMString	Feature
	DOMString	Version

Since the Node interface is never instantiated directly, the nodeType attribute contains a value that indicates the given instance's specific object type. Based on the nodeType, it is possible to cast a generic Node reference safely to a specific interface for further processing. Table 18-2 shows the node type values and their corresponding DOM interfaces, and Table 18-3 shows the values they provide for nodeName, nodeValue, and attributes attributes.

Table 18-2. DOM node types and interfaces

Node type	DOM interface
`ATTRIBUTE_NODE`	`Attr`
`CDATA_SECTION_NODE`	`CDATASection`
`COMMENT_NODE`	`Comment`
`DOCUMENT_FRAGMENT_NODE`	`DocumentFragment`
`DOCUMENT_NODE`	`Document`
`DOCUMENT_TYPE_NODE`	`DocumentType`
`ELEMENT_NODE`	`Element`
`ENTITY_NODE`	`Entity`
`ENTITY_REFERENCE_NODE`	`EntityReference`
`NOTATION_NODE`	`Notation`
`PROCESSING_INSTRUCTION_NODE`	`ProcessingInstruction`
`TEXT_NODE`	`Text`

Table 18-3. DOM node types and method results

Node type	nodeName	nodeValue	Attributes
`ATTRIBUTE_NODE`	att name	att value	null
`CDATA_SECTION_NODE`	`#cdata-section`	content	null
`COMMENT_NODE`	`#comment`	content	null
`DOCUMENT_FRAGMENT_NODE`	`#document-fragment`	null	null
`DOCUMENT_NODE`	`#document`	null	null
`DOCUMENT_TYPE_NODE`	document type name	null	null
`ELEMENT_NODE`	tag name	null	NamedNodeMap
`ENTITY_NODE`	entity name	null	null
`ENTITY_REFERENCE_NODE`	name of entity referenced	null	null
`NOTATION_NODE`	notation name	null	null
`PROCESSING_INSTRUCTION_NODE`	target	content excluding the target	null
`TEXT_NODE`	`#text`	content	null

Note that the nodeValue attribute returns the contents of simple text and comment nodes, but returns nothing for elements. Retrieving the text of an element requires inspecting the text nodes it contains.

18.3.1. The NodeList Interface

The NodeList interface provides access to the ordered content of a node. Most frequently, it is used to retrieve text nodes and child elements of element nodes. See Table 18-4 for a summary of the NodeList interface.

Table 18-4. NodeList interface

Type		Name	Read-only	DOM 2.0
Attributes
Long		length
Methods
Node		item
	Long	index

The NodeList interface is extremely basic and is generally combined with a loop to iterate over the children of a node.

18.3.2. The NamedNodeMap Interface

The NamedNodeMap interface is used for unordered collections whose contents are identified by name. In practice, this interface is used to access attributes. See Table 18-5 for a summary of the NamedNodeMap interface.

Table 18-5. NamedNodeMap interface

Type		Name	Read-only	DOM 2.0
Attributes
Long		length
Methods
Node		getNamedItem
	DOMString	name
Node		setNamedItem
	Node	arg
Node		removeNamedItem
	DOMString	name
Node		getNamedItemNS
	DOMString	namespaceURI
	DOMString	localName
Node		setNamedItemNS
	Node	arg
Node		removeNamedItemNS
	DOMString	namespaceURI
	DOMString	localName

18.3.3. Relating Document Structure to Nodes

Although the DOM doesn't specify an interface to cause a document to be parsed, it does specify how the document's syntax structures are encoded as DOM objects. A document is stored as a hierarchical tree structure, with each item in the tree linked to its parent, children, and siblings:

<sample bogus="value"><text_node>Test data.</text_node></sample>

Figure 18-1 shows how the preceding short sample document would be stored by a DOM parser.

Figure 18-1

Figure 18-1. Document storage and linkages

Each Node-derived object in a parsed DOM document contains references to its parent, child, and sibling nodes. These references make it possible for applications to enumerate document data using any number of standard tree-traversal algorithms. "Walking the tree" is a common approach to finding information stored in a DOM and is demonstrated in Example 18-1 at the end of this chapter.

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