javax.xml.namespace

## Interface NamespaceContext

-     public interface NamespaceContext

  Interface for read only XML Namespace context processing.

  An XML Namespace has the properties:

  - Namespace URI: Namespace name expressed as a URI to which the prefix is bound
  - prefix: syntactically, this is the part of the attribute name following the `XMLConstants.XMLNS_ATTRIBUTE` ("xmlns") in the Namespace declaration

  example: `<element xmlns:prefix="http://Namespace-name-URI">`

  All `get*(*)` methods operate in the current scope for Namespace URI and prefix resolution.

  Note that a Namespace URI can be bound to multiple prefixes in the current scope. This can occur when multiple `XMLConstants.XMLNS_ATTRIBUTE` ("xmlns") Namespace declarations occur in the same Start-Tag and refer to the same Namespace URI. e.g.

       <element xmlns:prefix1="http://Namespace-name-URI"
                xmlns:prefix2="http://Namespace-name-URI">

  This can also occur when the same Namespace URI is used in multiple `XMLConstants.XMLNS_ATTRIBUTE` ("xmlns") Namespace declarations in the logical parent element hierarchy. e.g.

       <parent xmlns:prefix1="http://Namespace-name-URI">
         <child xmlns:prefix2="http://Namespace-name-URI">
           ...
         </child>
       </parent>

  A prefix can only be bound to a single Namespace URI in the current scope.

  Since:
    1.5
  See Also:
    `javax.xml.XMLConstants for declarations of common XML values`, XML Schema Part2: Datatypes, Namespaces in XML, Namespaces in XML Errata

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `String` | `getNamespaceURI(String prefix)` Get Namespace URI bound to a prefix in the current scope.
    `String` | `getPrefix(String namespaceURI)` Get prefix bound to Namespace URI in the current scope.
    `Iterator` | `getPrefixes(String namespaceURI)` Get all prefixes bound to a Namespace URI in the current scope.

- - ### Method Detail

    - #### getNamespaceURI

          String getNamespaceURI(String prefix)

      Get Namespace URI bound to a prefix in the current scope.

      When requesting a Namespace URI by prefix, the following table describes the returned Namespace URI value for all possible prefix values:

      `getNamespaceURI(prefix)` return value for specified prefixes
      prefix parameter | Namespace URI return value
      `DEFAULT_NS_PREFIX` ("") | default Namespace URI in the current scope or ``XMLConstants.NULL_NS_URI("")`` when there is no default Namespace URI in the current scope
      bound prefix | Namespace URI bound to prefix in current scope
      unbound prefix | ``XMLConstants.NULL_NS_URI("")``
      `XMLConstants.XML_NS_PREFIX` ("xml") | `XMLConstants.XML_NS_URI` ("http://www.w3.org/XML/1998/namespace")
      `XMLConstants.XMLNS_ATTRIBUTE` ("xmlns") | `XMLConstants.XMLNS_ATTRIBUTE_NS_URI` ("http://www.w3.org/2000/xmlns/")
      `null` | `IllegalArgumentException` is thrown

      Parameters:
        `prefix` - prefix to look up
      Returns:
        Namespace URI bound to prefix in the current scope
      Throws:
        `IllegalArgumentException` - When `prefix` is `null`

    - #### getPrefix

          String getPrefix(String namespaceURI)

      Get prefix bound to Namespace URI in the current scope.

      To get all prefixes bound to a Namespace URI in the current scope, use `getPrefixes(String namespaceURI)`.

      When requesting a prefix by Namespace URI, the following table describes the returned prefix value for all Namespace URI values:

      `getPrefix(namespaceURI)` return value for specified Namespace URIs
      Namespace URI parameter | prefix value returned
      --- | ---
      <default Namespace URI> | `XMLConstants.DEFAULT_NS_PREFIX` ("")
      bound Namespace URI | prefix bound to Namespace URI in the current scope, if multiple prefixes are bound to the Namespace URI in the current scope, a single arbitrary prefix, whose choice is implementation dependent, is returned
      unbound Namespace URI | `null`
      `XMLConstants.XML_NS_URI` ("http://www.w3.org/XML/1998/namespace") | `XMLConstants.XML_NS_PREFIX` ("xml")
      `XMLConstants.XMLNS_ATTRIBUTE_NS_URI` ("http://www.w3.org/2000/xmlns/") | `XMLConstants.XMLNS_ATTRIBUTE` ("xmlns")
      `null` | `IllegalArgumentException` is thrown

      Parameters:
        `namespaceURI` - URI of Namespace to lookup
      Returns:
        prefix bound to Namespace URI in current context
      Throws:
        `IllegalArgumentException` - When `namespaceURI` is `null`

    - #### getPrefixes

          Iterator getPrefixes(String namespaceURI)

      Get all prefixes bound to a Namespace URI in the current scope.

      An Iterator over String elements is returned in an arbitrary, implementation dependent, order.

      The `Iterator` is not modifiable. e.g. the `remove()` method will throw `UnsupportedOperationException`.

      When requesting prefixes by Namespace URI, the following table describes the returned prefixes value for all Namespace URI values:

      `getPrefixes(namespaceURI)` return value for specified Namespace URIs
      Namespace URI parameter | prefixes value returned
      --- | ---
      bound Namespace URI, including the <default Namespace URI> | `Iterator` over prefixes bound to Namespace URI in the current scope in an arbitrary, implementation dependent, order
      unbound Namespace URI | empty `Iterator`
      `XMLConstants.XML_NS_URI` ("http://www.w3.org/XML/1998/namespace") | `Iterator` with one element set to `XMLConstants.XML_NS_PREFIX` ("xml")
      `XMLConstants.XMLNS_ATTRIBUTE_NS_URI` ("http://www.w3.org/2000/xmlns/") | `Iterator` with one element set to `XMLConstants.XMLNS_ATTRIBUTE` ("xmlns")
      `null` | `IllegalArgumentException` is thrown

      Parameters:
        `namespaceURI` - URI of Namespace to lookup
      Returns:
        `Iterator` for all prefixes bound to the Namespace URI in the current scope
      Throws:
        `IllegalArgumentException` - When `namespaceURI` is `null`

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