Package net.sf.saxon.value
Class SingletonClosure
- java.lang.Object
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- net.sf.saxon.value.Value
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- net.sf.saxon.value.Closure
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- net.sf.saxon.value.SingletonClosure
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- All Implemented Interfaces:
java.io.Serializable
,SequenceIterable
,ValueRepresentation
public class SingletonClosure extends Closure
A SingletonClosure represents a value that has not yet been evaluated: the value is represented by an expression, together with saved values of all the context variables that the expression depends on. The value of a SingletonClosure is always either a single item or an empty sequence.The expression may depend on local variables and on the context item; these values are held in the saved XPathContext object that is kept as part of the Closure, and they will always be read from that object. The expression may also depend on global variables; these are unchanging, so they can be read from the Bindery in the normal way. Expressions that depend on other contextual information, for example the values of position(), last(), current(), current-group(), should not be evaluated using this mechanism: they should always be evaluated eagerly. This means that the Closure does not need to keep a copy of these context variables.
- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.value.Closure
depth, expression, inputIterator, savedXPathContext
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Fields inherited from class net.sf.saxon.value.Value
EMPTY_CLASS_ARRAY, INDETERMINATE_ORDERING
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Fields inherited from interface net.sf.saxon.om.ValueRepresentation
EMPTY_VALUE_ARRAY
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Constructor Summary
Constructors Constructor Description SingletonClosure(Expression exp, XPathContext context)
Constructor should not be called directly, instances should be made using the make() method.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description Item
asItem()
Return the value in the form of an Itemint
getLength()
Get the length of the sequenceItem
itemAt(int n)
Get the n'th item in the sequence (starting from 0).SequenceIterator
iterate()
Evaluate the expression in a given context to return an iterator over a sequenceValue
materialize()
Return a value containing all the items in the sequence returned by this SequenceIteratorvoid
process(XPathContext context)
Process the expression by writing the value to the current Receiver-
Methods inherited from class net.sf.saxon.value.Closure
getCardinality, getItemType, make, makeIteratorClosure, reduce, saveContext
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Methods inherited from class net.sf.saxon.value.Value
asItem, asIterator, asValue, checkPermittedContents, convertToJava, effectiveBooleanValue, equals, fromItem, getCanonicalLexicalRepresentation, getIterator, getSchemaComparable, getStringValue, getStringValueCS, iterate, makeQNameValue, stringToNumber, toString
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Constructor Detail
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SingletonClosure
public SingletonClosure(Expression exp, XPathContext context) throws XPathException
Constructor should not be called directly, instances should be made using the make() method.- Parameters:
exp
- the expression to be lazily evaluatedcontext
- the context in which the expression should be evaluated- Throws:
XPathException
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Method Detail
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iterate
public SequenceIterator iterate() throws XPathException
Evaluate the expression in a given context to return an iterator over a sequence- Overrides:
iterate
in classClosure
- Returns:
- an iterator over the sequence of items
- Throws:
XPathException
- if a dynamic error occurs. This is possible only in the case of values that are materialized lazily, that is, where the iterate() method leads to computation of an expression that delivers the values.
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process
public void process(XPathContext context) throws XPathException
Process the expression by writing the value to the current Receiver- Overrides:
process
in classClosure
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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asItem
public Item asItem() throws XPathException
Return the value in the form of an Item- Overrides:
asItem
in classValue
- Returns:
- the value in the form of an Item
- Throws:
XPathException
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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- Overrides:
itemAt
in classValue
- Parameters:
n
- position of the required item, counting from zero.- Returns:
- the n'th item in the sequence, where the first item in the sequence is numbered zero. If n is negative or >= the length of the sequence, returns null.
- Throws:
XPathException
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getLength
public int getLength() throws XPathException
Get the length of the sequence- Overrides:
getLength
in classValue
- Returns:
- the number of items in the sequence
- Throws:
XPathException
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materialize
public Value materialize() throws XPathException
Return a value containing all the items in the sequence returned by this SequenceIterator- Returns:
- the corresponding value
- Throws:
XPathException
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