com.saxonica.deploy
Class ItemClosure

java.lang.Object
  net.sf.saxon.value.Value
      com.saxonica.deploy.ItemClosure

All Implemented Interfaces:

Serializable, SequenceIterable, ValueRepresentation

public class ItemClosure
extends Value

An ItemClosure represents a singleton value that has not yet been evaluated: the value is represented by an EvaluableItem object which performs the evaluation. Once this has been called the first time, the actual item value is stored in the ItemClosure for use on subsequent occasions.

This class is currently used only by the Saxon-EE Java code-generator.

See Also:

Serialized Form

Field Summary

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

INDETERMINATE_ORDERING

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

EMPTY_VALUE_ARRAY

Constructor Summary

protected	ItemClosure()
	ItemClosure(EvaluableItem evaluator, XPathContext context, int primitiveType) Create an ItemClosure

Method Summary

Item	asItem() Evaluate as a singleton item (or empty sequence).
int	getCardinality() Get the cardinality.
ItemType	getItemType(TypeHierarchy th) Get the static item type
int	getLength() Get the length of the value.
Comparable	getSchemaComparable() Get a Comparable value that implements the XML Schema ordering comparison semantics for this value.
Item	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 sequence
Value	reduce() Reduce a value to its simplest form.

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

asItem, asIterator, asValue, checkPermittedContents, convertToJava, effectiveBooleanValue, equals, fromItem, getCanonicalLexicalRepresentation, getIterator, getStringValue, getStringValueCS, hashCode, isIdentical, iterate, process

Methods inherited from class java.lang.Object

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

Constructor Detail

ItemClosure

protected ItemClosure()

ItemClosure

public ItemClosure(EvaluableItem evaluator,
                   XPathContext context,
                   int primitiveType)

Create an ItemClosure

Parameters:

evaluator - used to do deferred evaluation of the item

context - XPath dynamic context for evaluating the item

primitiveType - the expected primitive type of the result

Method Detail

getItemType

public ItemType getItemType(TypeHierarchy th)

Get the static item type

Overrides:

getItemType in class Value

Parameters:

th - the type hierarchy cache

Returns:

for the default implementation: AnyItemType (not known)

getCardinality

public int getCardinality()

Get the cardinality. This method is intended to be implemented in a subclass, but if it is not implemented, the fallback implementation simply returns StaticProperty.ALLOWS_ZERO_OR_MORE

Overrides:

getCardinality in class Value

Returns:

the cardinality

asItem

public Item asItem()
            throws XPathException

Evaluate as a singleton item (or empty sequence). Note: this implementation returns the first item in the sequence. The method should not be used unless appropriate type-checking has been done to ensure that the value will be a singleton.

Overrides:

asItem in class Value

Returns:

the value in the form of an Item

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 Values, but its real benefits come for a sequence Value stored extensionally (or for a MemoClosure, once all the values have been read)

Overrides:

itemAt in class Value

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

iterate

public SequenceIterator iterate()
                         throws XPathException

Evaluate the expression in a given context to return an iterator over a sequence

Specified by:

iterate in class Value

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.

reduce

public Value reduce()
             throws XPathException

Reduce a value to its simplest form. If the value is a closure or some other form of deferred value such as a FunctionCallPackage, then it is reduced to a SequenceExtent. If it is a SequenceExtent containing a single item, then it is reduced to that item. One consequence that is exploited by class FilterExpression is that if the value is a singleton numeric value, then the result will be an instance of NumericValue

Overrides:

reduce in class Value

Returns:

the value in simplified form

Throws:

XPathException

getLength

public int getLength()
              throws XPathException

Get the length of the value. Note: this consumes the iterator!

Overrides:

getLength in class Value

Returns:

the number of items in the sequence

Throws:

XPathException

getSchemaComparable

public Comparable getSchemaComparable()

Get a Comparable value that implements the XML Schema ordering comparison semantics for this value. The default implementation returns "this", which ensures that comparisons between list values are handled by the equals() and compareTo() methods on this class itself. This is overridden for atomic values.

In the case of data types that are partially ordered, the returned Comparable extends the standard semantics of the compareTo() method by returning the value Value.INDETERMINATE_ORDERING when there is no defined order relationship between two given values.

Overrides:

getSchemaComparable in class Value

Returns:

a Comparable that follows XML Schema comparison rules