QName

AI-generated Key Takeaways

• QName represents a qualified name consisting of a Namespace URI, local part, and prefix, as defined in XML specifications.

• Equality and hash code are determined solely by the Namespace URI and local part, with the prefix being excluded from these computations.

• Although the prefix is included to retain lexical information, it's not used for equality comparisons or hash code calculations.

• If the Namespace URI isn't specified, it defaults to XMLConstants.NULL_NS_URI, and if the prefix isn't specified, it defaults to XMLConstants.DEFAULT_NS_PREFIX.

• QName is immutable, meaning its value cannot be changed after it's created.

public class QName extends Object
implements Serializable

QName represents a qualified name as defined in the XML specifications: XML Schema Part2: Datatypes specification, Namespaces in XML, Namespaces in XML Errata.

The value of a QName contains a Namespace URI, local part and prefix.

The prefix is included in QName to retain lexical information when present in an XML input source. The prefix is NOT used in QName.equals(Object) or to compute the QName.hashCode(). Equality and the hash code are defined using only the Namespace URI and local part.

If not specified, the Namespace URI is set to XMLConstants.NULL_NS_URI. If not specified, the prefix is set to XMLConstants.DEFAULT_NS_PREFIX.

QName is immutable.

See Also

• XML Schema Part2: Datatypes specification
• Namespaces in XML
• Namespaces in XML Errata

Public Constructor Summary

	QName(String namespaceURI, String localPart) QName constructor specifying the Namespace URI and local part.
	QName(String namespaceURI, String localPart, String prefix) QName constructor specifying the Namespace URI, local part and prefix.
	QName(String localPart) QName constructor specifying the local part.

Public Method Summary

final boolean	equals(Object objectToTest) Test this QName for equality with another Object.
String	getLocalPart() Get the local part of this QName.
String	getNamespaceURI() Get the Namespace URI of this QName.
String	getPrefix() Get the prefix of this QName.
final int	hashCode() Generate the hash code for this QName.
String	toString() String representation of this QName.
static QName	valueOf(String qNameAsString) QName derived from parsing the formatted String.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public QName (String namespaceURI, String localPart)

QName constructor specifying the Namespace URI and local part.

If the Namespace URI is null, it is set to XMLConstants.NULL_NS_URI. This value represents no explicitly defined Namespace as defined by the Namespaces in XML specification. This action preserves compatible behavior with QName 1.0. Explicitly providing the XMLConstants.NULL_NS_URI value is the preferred coding style.

If the local part is null an IllegalArgumentException is thrown. A local part of "" is allowed to preserve compatible behavior with QName 1.0.

When using this constructor, the prefix is set to XMLConstants.DEFAULT_NS_PREFIX.

The Namespace URI is not validated as a URI reference. The local part is not validated as a NCName as specified in Namespaces in XML.

Parameters

namespaceURI	Namespace URI of the QName
localPart	local part of the QName

See Also

• QName(String namespaceURI, String localPart, String prefix)

public QName (String namespaceURI, String localPart, String prefix)

QName constructor specifying the Namespace URI, local part and prefix.

If the Namespace URI is null, it is set to XMLConstants.NULL_NS_URI. This value represents no explicitly defined Namespace as defined by the Namespaces in XML specification. This action preserves compatible behavior with QName 1.0. Explicitly providing the XMLConstants.NULL_NS_URI value is the preferred coding style.

If the local part is null an IllegalArgumentException is thrown. A local part of "" is allowed to preserve compatible behavior with QName 1.0.

If the prefix is null, an IllegalArgumentException is thrown. Use XMLConstants.DEFAULT_NS_PREFIX to explicitly indicate that no prefix is present or the prefix is not relevant.

The Namespace URI is not validated as a URI reference. The local part and prefix are not validated as a NCName as specified in Namespaces in XML.

Parameters

namespaceURI	Namespace URI of the QName
localPart	local part of the QName
prefix	prefix of the QName

public QName (String localPart)

QName constructor specifying the local part.

If the local part is null an IllegalArgumentException is thrown. A local part of "" is allowed to preserve compatible behavior with QName 1.0.

When using this constructor, the Namespace URI is set to XMLConstants.NULL_NS_URI and the prefix is set to XMLConstants.DEFAULT_NS_PREFIX.

In an XML context, all Element and Attribute names exist in the context of a Namespace. Making this explicit during the construction of a QName helps prevent hard to diagnosis XML validity errors. The constructors QName(String namespaceURI, String localPart) and QName(String, String, String) are preferred.

The local part is not validated as a NCName as specified in Namespaces in XML.

Parameters

localPart	local part of the QName

See Also

• QName(String namespaceURI, String localPart)
• QName(String namespaceURI, String localPart, String prefix)

Public Methods

public final boolean equals (Object objectToTest)

Test this QName for equality with another Object.

If the Object to be tested is not a QName or is null, then this method returns false.

Two QNames are considered equal if and only if both the Namespace URI and local part are equal. This method uses String.equals() to check equality of the Namespace URI and local part. The prefix is NOT used to determine equality.

This method satisfies the general contract of Object.equals(Object)

Parameters

objectToTest	the Object to test for equality with this QName

Returns

• true if the given Object is equal to this QName else false

public String getLocalPart ()

Get the local part of this QName.

Returns

• local part of this QName

public String getNamespaceURI ()

Get the Namespace URI of this QName.

Returns

• Namespace URI of this QName

public String getPrefix ()

Get the prefix of this QName.

The prefix assigned to a QName might NOT be valid in a different context. For example, a QName may be assigned a prefix in the context of parsing a document but that prefix may be invalid in the context of a different document.

Returns

• prefix of this QName

public final int hashCode ()

Generate the hash code for this QName.

The hash code is calculated using both the Namespace URI and the local part of the QName. The prefix is NOT used to calculate the hash code.

This method satisfies the general contract of Object.hashCode().

Returns

• hash code for this QName Object

public String toString ()

String representation of this QName.

The commonly accepted way of representing a QName as a String was defined by James Clark. Although this is not a standard specification, it is in common use, e.g. Transformer.setParameter(String, Object). This implementation represents a QName as: "{" + Namespace URI + "}" + local part. If the Namespace URI .equals(XMLConstants.NULL_NS_URI), only the local part is returned. An appropriate use of this method is for debugging or logging for human consumption.

Note the prefix value is NOT returned as part of the String representation.

This method satisfies the general contract of Object.toString().

Returns

• String representation of this QName

public static QName valueOf (String qNameAsString)

QName derived from parsing the formatted String.

If the String is null or does not conform to QName.toString() formatting, an IllegalArgumentException is thrown.

The String MUST be in the form returned by QName.toString().

The commonly accepted way of representing a QName as a String was defined by James Clark. Although this is not a standard specification, it is in common use, e.g. Transformer.setParameter(String, Object). This implementation parses a String formatted as: "{" + Namespace URI + "}" + local part. If the Namespace URI .equals(XMLConstants.NULL_NS_URI), only the local part should be provided.

The prefix value CANNOT be represented in the String and will be set to XMLConstants.DEFAULT_NS_PREFIX.

This method does not do full validation of the resulting QName.

The Namespace URI is not validated as a URI reference. The local part is not validated as a NCName as specified in Namespaces in XML.

Parameters

qNameAsString	String representation of the QName

Returns

• QName corresponding to the given String

See Also

• QName.toString()