Package net.sf.saxon.expr
Class Literal
- java.lang.Object
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- net.sf.saxon.expr.Expression
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- net.sf.saxon.expr.Literal
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,LocationProvider
,SaxonLocator
,EvaluableItem
,SequenceIterable
,InstructionInfo
,org.xml.sax.Locator
- Direct Known Subclasses:
StringLiteral
public class Literal extends Expression
A Literal is an expression whose value is constant: it is a class that implements the Expression interface as a wrapper around a Value. This may derive from an actual literal in an XPath expression or query, or it may be the result of evaluating a constant subexpression such as true() or xs:date('2007-01-16')- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description PathMap.PathMapNodeSet
addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.int
computeCardinality()
Determine the cardinalityint
computeSpecialProperties()
Compute the static properties of this expression (other than its type).Expression
copy()
Copy an expression.boolean
effectiveBooleanValue(XPathContext context)
Get the effective boolean value of the expression.boolean
equals(java.lang.Object obj)
Determine whether two literals are equal, when considered as expressions.java.lang.CharSequence
evaluateAsString(XPathContext context)
Evaluate an expression as a String.Item
evaluateItem(XPathContext context)
Evaluate as a singleton item (or empty sequence).void
evaluatePendingUpdates(XPathContext context, PendingUpdateList pul)
Evaluate an updating expression, adding the results to a Pending Update List.void
explain(ExpressionPresenter out)
Diagnostic print of expression structure.int
getDependencies()
Determine which aspects of the context the expression depends on.ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items in the expression, if possibleValue
getValue()
Get the value represented by this Literalint
hashCode()
Return a hash code to support the equals() functionstatic boolean
isAtomic(Expression exp)
Test whether the literal wraps an atomic value.static boolean
isConstantBoolean(Expression exp, boolean value)
Test if a literal represents the boolean value truestatic boolean
isConstantOne(Expression exp)
Test if a literal represents the integer value 1static boolean
isEmptySequence(Expression exp)
Test whether the literal explicitly wraps an empty sequence.SequenceIterator
iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence.static Literal
makeEmptySequence()
Make an empty-sequence literalstatic Literal
makeLiteral(Value value)
Create a literal as a wrapper around a Value (factory method)Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Optimize an expressionvoid
process(XPathContext context)
Process the value as an instruction, without returning any tail callsExpression
simplify(ExpressionVisitor visitor)
Simplify an expressionjava.lang.String
toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.Expression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
TypeCheck an expression-
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, dynamicError, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, iterateSubExpressions, markTailFunctionCalls, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError
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Constructor Detail
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Literal
public Literal(Value value)
Create a literal as a wrapper around a Value- Parameters:
value
- the value of this literal
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Method Detail
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makeLiteral
public static Literal makeLiteral(Value value)
Create a literal as a wrapper around a Value (factory method)- Parameters:
value
- the value of this literal- Returns:
- the Literal
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makeEmptySequence
public static Literal makeEmptySequence()
Make an empty-sequence literal- Returns:
- a literal whose value is the empty sequence
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getValue
public Value getValue()
Get the value represented by this Literal- Returns:
- the constant value
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simplify
public final Expression simplify(ExpressionVisitor visitor)
Simplify an expression- Overrides:
simplify
in classExpression
- Parameters:
visitor
- an expression visitor- Returns:
- for a Value, this always returns the value unchanged
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typeCheck
public final Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
TypeCheck an expression- Overrides:
typeCheck
in classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set toType.ITEM_TYPE
- Returns:
- for a Value, this always returns the value unchanged
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optimize
public final Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
Optimize an expression- Overrides:
optimize
in classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set toType.ITEM_TYPE
- Returns:
- for a Value, this always returns the value unchanged
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getItemType
public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items in the expression, if possible- Specified by:
getItemType
in classExpression
- Parameters:
th
- The TypeHierarchy. Can be null if the target is an AtomicValue.- Returns:
- for the default implementation: AnyItemType (not known)
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computeCardinality
public int computeCardinality()
Determine the cardinality- Specified by:
computeCardinality
in classExpression
- Returns:
- the computed cardinality, as one of the values
StaticProperty.ALLOWS_ZERO_OR_ONE
,StaticProperty.EXACTLY_ONE
,StaticProperty.ALLOWS_ONE_OR_MORE
,StaticProperty.ALLOWS_ZERO_OR_MORE
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computeSpecialProperties
public int computeSpecialProperties()
Compute the static properties of this expression (other than its type). For a Value, the only special property isStaticProperty.NON_CREATIVE
.- Overrides:
computeSpecialProperties
in classExpression
- Returns:
- the value
StaticProperty.NON_CREATIVE
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copy
public Expression copy()
Copy an expression. This makes a deep copy.- Specified by:
copy
in classExpression
- Returns:
- the copy of the original expression
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addToPathMap
public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.- Overrides:
addToPathMap
in classExpression
- Parameters:
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
-- Returns:
- the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression
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getDependencies
public final int getDependencies()
Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.VARIABLES and StaticProperty.CURRENT_NODE- Overrides:
getDependencies
in classExpression
- Returns:
- for a Value, this always returns zero.
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.- Specified by:
iterate
in interfaceSequenceIterable
- Overrides:
iterate
in classExpression
- Parameters:
context
- supplies the context for evaluation- Returns:
- a SequenceIterator that can be used to iterate over the result of the expression
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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evaluateItem
public Item evaluateItem(XPathContext context) 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.- Specified by:
evaluateItem
in interfaceEvaluableItem
- Overrides:
evaluateItem
in classExpression
- Parameters:
context
- The context in which the expression is to be evaluated- Returns:
- the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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process
public void process(XPathContext context) throws XPathException
Process the value as an instruction, without returning any tail calls- Overrides:
process
in classExpression
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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evaluateAsString
public java.lang.CharSequence evaluateAsString(XPathContext context) throws XPathException
Description copied from class:Expression
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.- Overrides:
evaluateAsString
in classExpression
- 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
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effectiveBooleanValue
public boolean effectiveBooleanValue(XPathContext context) throws XPathException
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.- Overrides:
effectiveBooleanValue
in classExpression
- Parameters:
context
- The context in which the expression is to be evaluated- Returns:
- the effective boolean value
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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evaluatePendingUpdates
public void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) throws XPathException
Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException. The implementation for a literal representing an empty sequence, however, is a no-op.- Overrides:
evaluatePendingUpdates
in classExpression
- Parameters:
context
- the XPath dynamic evaluation contextpul
- the pending update list to which the results should be written- Throws:
XPathException
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equals
public boolean equals(java.lang.Object obj)
Determine whether two literals are equal, when considered as expressions.- Overrides:
equals
in classjava.lang.Object
- Parameters:
obj
- the other expression- Returns:
- true if the two literals are equal
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hashCode
public int hashCode()
Return a hash code to support the equals() function- Overrides:
hashCode
in classjava.lang.Object
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toString
public java.lang.String toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax- Overrides:
toString
in classExpression
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explain
public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
explain
in classExpression
- Parameters:
out
- the expression presenter used to display the structure
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isAtomic
public static boolean isAtomic(Expression exp)
Test whether the literal wraps an atomic value. (Note, if this method returns false, this still leaves the possibility that the literal wraps a sequence that happens to contain a single atomic value).- Parameters:
exp
- an expression- Returns:
- if the expression is a literal and the literal wraps an AtomicValue
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isEmptySequence
public static boolean isEmptySequence(Expression exp)
Test whether the literal explicitly wraps an empty sequence. (Note, if this method returns false, this still leaves the possibility that the literal wraps a sequence that happens to be empty).- Parameters:
exp
- an expression- Returns:
- if the expression is a literal and the literal wraps an AtomicValue
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isConstantBoolean
public static boolean isConstantBoolean(Expression exp, boolean value)
Test if a literal represents the boolean value true- Parameters:
exp
- an expressionvalue
- true or false- Returns:
- if the expression is a literal and the literal represents the boolean value given in the second argument
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isConstantOne
public static boolean isConstantOne(Expression exp)
Test if a literal represents the integer value 1- Parameters:
exp
- an expression- Returns:
- if the expression is a literal and the literal represents the integer value 1
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