19.3 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 object within a DOM document tree 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 19-1, this interface contains information about the type, location, name , and value of the corresponding underlying document data.

Table 19-1. The Node interface

Name

Type

Read-only

2.0

3.0

Attributes

       

attributes

NamedNodeMap

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baseURI

DOMString

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childNodes

NodeList

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firstChild

Node

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lastChild

Node

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localName

DOMString

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namespaceURI

DOMString

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nextSibling

Node

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nodeName

DOMString

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nodeType

unsigned short

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nodeValue

DOMString

     

ownerDocument

Document

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parentNode

Node

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prefix

DOMString

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previousSibling

Node

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textContent

DOMString

    figs/check.gif

Methods

       

appendChild

Node

     

cloneNode

Node

     

compareDocumentPosition

unsigned short

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getFeature

DOMObject

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getUserData

DOMUserData

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hasAttributes

boolean

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hasChildNodes

boolean

     

insertBefore

Node

     

isDefaultNamespace

boolean

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isEqualNode

boolean

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isSameNode

boolean

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isSupported

boolean

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lookupNamespaceURI

DOMString

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lookupPrefix

DOMString

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normalize

void

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removeChild

Node

     

replaceChild

Node

     

setUserData

DOMUserData

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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 19-2 shows the node type values and their corresponding DOM interfaces, and Table 19-3 shows the values they provide for nodeName , nodeValue , and attributes attributes.

Table 19-2. The 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 19-3. The 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. Prior to DOM Level 3, retrieving the text content of an element required locating any child Text nodes it might contain, but DOM Level 3 introduced the getTextContent( ) and setTextContent() convenience methods.

19.3.1 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 19-4 for a summary of the NodeList interface.

Table 19-4. The NodeList interface

Name

Type

Read-only

2.0

3.0

Attribute

       

length

Long

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Method

       

item

Node

     

The NodeList interface is extremely basic and is generally combined with a loop to iterate through the children of a node, as in the following example:

 NodeList nl = nd.getChildNodes( ); for (int i = 0; i < nl.getLength( ); i++) {   Node ndChild = nl.item(i);   if (ndChild.getNodeType( ) =  = Node.COMMENT_NODE) {     System.out.println("found comment: " + ndChild.getNodeValue( ));   } } 

19.3.2 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 of elements. See Table 19-5 for a summary of the NamedNodeMap interface.

Table 19-5. The NamedNodeMap interface

Name

Type

Read-only

2.0

3.0

Attribute

       

length

Long

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Methods

       

getNamedItem

Node

     

getNamedItemNS

Node

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removeNamedItem

Node

     

removeNamedItemNS

Node

     

setNamedItem

Node

     

setNamedItemNS

Node

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19.3.3 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 19-1 shows how the preceding short sample document would be stored by a DOM parser.

Figure 19-1. Document storage and linkages
figs/xian3_1901.gif

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 19-1 at the end of this chapter.



XML in a Nutshell
XML in a Nutshell, Third Edition
ISBN: 0596007647
EAN: 2147483647
Year: 2003
Pages: 232

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