Package net.sf.saxon.value
Class EmptySequence
java.lang.Object
net.sf.saxon.value.Value
net.sf.saxon.value.EmptySequence
- All Implemented Interfaces:
Serializable
,Expression
,ValueRepresentation
An EmptySequence object represents a sequence containing no members.
- See Also:
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Field Summary
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
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Method Summary
Modifier and TypeMethodDescriptionvoid
display
(int level, PrintStream out, Configuration config) Diagnostic print of expression structureboolean
effectiveBooleanValue
(XPathContext context) Get the effective boolean value - always falseboolean
Is this expression the same as another expression?int
Determine the static cardinalityint
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().static EmptySequence
Get the implicit instance of this classDetermine the item typefinal int
Get the length of the sequenceint
Get the static properties of this expression (other than its type).int
hashCode()
Return a hash code to support the equals() functioniterate
(XPathContext context) Return an iteration over the sequenceMethods inherited from class net.sf.saxon.value.Value
asItem, asIterator, asValue, checkPermittedContents, convert, convertJavaObjectToXPath, convertToJava, evaluateAsString, evaluateItem, getDependencies, getIterator, getParentExpression, getStringValue, getStringValueCS, itemAt, iterateSubExpressions, makeQNameValue, optimize, process, promote, reduce, simplify, stringToNumber, toString, typeCheck
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Method Details
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getInstance
Get the implicit instance of this class -
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. -
iterate
Return an iteration over the sequence- 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
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getItemType
Determine the item type- Specified by:
getItemType
in interfaceExpression
- Overrides:
getItemType
in classValue
- Parameters:
th
-- Returns:
- for the default implementation: AnyItemType (not known)
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getCardinality
public int getCardinality()Determine the static cardinality- Specified by:
getCardinality
in interfaceExpression
- Overrides:
getCardinality
in classValue
- 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).
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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 interfaceExpression
- Overrides:
getSpecialProperties
in classValue
- Returns:
StaticProperty.NON_CREATIVE
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getLength
public final int getLength()Get the length of the sequence -
equals
Is this expression the same as another expression?- Overrides:
equals
in classValue
- Throws:
ClassCastException
- if the values are not comparable
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hashCode
public int hashCode()Description copied from class:Value
Return a hash code to support the equals() function -
effectiveBooleanValue
Get the effective boolean value - always false- Specified by:
effectiveBooleanValue
in interfaceExpression
- Overrides:
effectiveBooleanValue
in classValue
- Parameters:
context
- The context in which the expression is to be evaluated- Returns:
- the effective boolean value
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display
Diagnostic print of expression structure- Specified by:
display
in interfaceExpression
- Overrides:
display
in classValue
- Parameters:
level
- indentation level for this expressionout
- Output destinationconfig
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