net.sf.saxon.value

Class SingletonNode

java.lang.Object

net.sf.saxon.value.Value

net.sf.saxon.value.SingletonNode

All Implemented Interfaces:

java.io.Serializable, Expression, ValueRepresentation

public class SingletonNode
extends Value

A value that is a sequence containing zero or one nodes

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected NodeInfo	node

Fields inherited from class net.sf.saxon.value.Value

EMPTY_CLASS_ARRAY

Fields inherited from interface net.sf.saxon.expr.Expression

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Fields inherited from interface net.sf.saxon.om.ValueRepresentation

EMPTY_VALUE_ARRAY

Constructor Summary

Constructors

Constructor and Description
SingletonNode(NodeInfo node) Create a node-set containing zero or one nodes

Method Summary

Modifier and Type	Method and Description
java.lang.Object	convertToJava(java.lang.Class target, XPathContext context) Convert to Java object (for passing to external functions)
void	display(int depth, java.io.PrintStream out, Configuration config) Diagnostic display
boolean	effectiveBooleanValue(XPathContext context) Get the effective boolean value
java.lang.String	evaluateAsString(XPathContext context) Evaluate an expression as a String.
Item	evaluateItem(XPathContext context) Evaluate as an item
int	getCardinality() Determine the static cardinality
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items in the expression.
int	getLength() Get the length of the sequence
NodeInfo	getNode() Get the node that forms the node-set.
int	getSpecialProperties() Get the static properties of this expression (other than its type).
java.lang.String	getStringValue() Convert the value to a string, using the serialization rules.
Item	itemAt(int n) Get the n'th item in the sequence (starting from 0).
SequenceIterator	iterate(XPathContext context) Return an enumeration of this nodeset value.
void	process(XPathContext context) Process the instruction, without returning any tail calls

Methods inherited from class net.sf.saxon.value.Value

asItem, asIterator, asValue, checkPermittedContents, convert, convertJavaObjectToXPath, equals, getDependencies, getIterator, getParentExpression, getStringValueCS, hashCode, iterateSubExpressions, makeQNameValue, optimize, promote, reduce, simplify, stringToNumber, toString, typeCheck

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

node

protected NodeInfo node

Constructor Detail

SingletonNode

public SingletonNode(NodeInfo node)

Create a node-set containing zero or one nodes

Parameters:

node - The node to be contained in the node-set, or null if the node-set is to be empty

Method Detail

getImplementationMethod

public int getImplementationMethod()

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is prefered.

process

public void process(XPathContext context)
             throws XPathException

Process the instruction, without returning any tail calls

Specified by:

process in interface Expression

Overrides:

process in class Value

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the items in the expression. This method determines the most precise type that it can, because it is called when testing that the node conforms to a required type.

Specified by:

getItemType in interface Expression

Overrides:

getItemType in class Value

Parameters:

th -

Returns:

the most precise possible type of the node.

getCardinality

public int getCardinality()

Determine the static cardinality

Specified by:

getCardinality in interface Expression

Overrides:

getCardinality in class Value

Returns:

one of the values StaticProperty.ALLOWS_ONE, StaticProperty.ALLOWS_ZERO_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

getLength

public int getLength()
              throws XPathException

Get the length of the sequence

Overrides:

getLength in class Value

Throws:

XPathException

itemAt

public Item itemAt(int n)
            throws XPathException

Get the n'th item in the sequence (starting from 0). This is defined for all SequenceValues, but its real benefits come for a SequenceValue stored extensionally (or for a MemoClosure, once all the values have been read)

Overrides:

itemAt in class Value

Throws:

XPathException

getNode

public NodeInfo getNode()

Get the node that forms the node-set. Return null if there is none.

getSpecialProperties

public int getSpecialProperties()

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Specified by:

getSpecialProperties in interface Expression

Overrides:

getSpecialProperties in class Value

Returns:

StaticProperty.NON_CREATIVE

iterate

public SequenceIterator iterate(XPathContext context)

Return an enumeration of this nodeset value.

Parameters:

context - The context in which the expression is to be evaluated. Note that this context must contain a stackframe with sufficient slots to allow evaluation of any variables contained in the expression (including variables allocated internally by the optimizer)

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

evaluateItem

public Item evaluateItem(XPathContext context)

Evaluate as an item

Specified by:

evaluateItem in interface Expression

Overrides:

evaluateItem in class Value

Parameters:

context - The context in which the expression is to be evaluated. Note that this context must contain a stackframe with sufficient slots to allow evaluation of any variables contained in the expression (including variables allocated internally by the optimizer)

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)

Get the effective boolean value

Specified by:

effectiveBooleanValue in interface Expression

Overrides:

effectiveBooleanValue in class Value

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the effective boolean value

getStringValue

public java.lang.String getStringValue()

Convert the value to a string, using the serialization rules. For atomic values this is the same as a cast; for sequence values it gives a space-separated list. For QNames and NOTATIONS, or lists containing them, it fails.

Specified by:

getStringValue in interface ValueRepresentation

Overrides:

getStringValue in class Value

evaluateAsString

public java.lang.String evaluateAsString(XPathContext context)
                                  throws XPathException

Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.

Specified by:

evaluateAsString in interface Expression

Overrides:

evaluateAsString in class Value

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".

Throws:

XPathException - if any dynamic error occurs evaluating the expression

display

public void display(int depth,
                    java.io.PrintStream out,
                    Configuration config)

Diagnostic display

Specified by:

display in interface Expression

Overrides:

display in class Value

Parameters:

depth - indentation level for this expression

out - Output destination

convertToJava

public java.lang.Object convertToJava(java.lang.Class target,
                                      XPathContext context)
                               throws XPathException

Convert to Java object (for passing to external functions)

Overrides:

convertToJava in class Value

Throws:

XPathException