net.sf.saxon.expr

Class Literal

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.Literal

All Implemented Interfaces:

IdentityComparable

Direct Known Subclasses:

FunctionLiteral, 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 GroundedValue. 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')

Field Summary

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Literal(GroundedValue value) Create a literal as a wrapper around a Value

Method Summary

Methods

Modifier and Type	Method and Description
PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
int	computeCardinality() Determine the cardinality
int	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(Object obj) Determine whether two literals are equal, when considered as expressions.
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	export(ExpressionPresenter out) Diagnostic print of expression structure.
static void	exportAtomicValue(AtomicValue value, ExpressionPresenter out)
static void	exportValue(Sequence value, ExpressionPresenter out)
int	getCost() Return the estimated cost of evaluating an expression.
int	getDependencies() Determine which aspects of the context the expression depends on.
ExpressionCompiler	getExpressionCompiler() Return the compiler of the Literal expression
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
IntegerValue[]	getIntegerBounds() For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.
ItemType	getItemType() Determine the data type of the items in the expression, if possible
protected StreamingAdjunct	getStreamingAdjunct() Get an object that supports streamed evaluation of this expression
GroundedValue	getValue() Get the value represented by this Literal
int	hashCode() Return a hash code to support the equals() function
static 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 true
static boolean	isConstantOne(Expression exp) Test if a literal represents the integer value 1
static boolean	isEmptySequence(Expression exp) Test whether the literal explicitly wraps an empty sequence.
boolean	isSubtreeExpression() Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.
boolean	isVacuousExpression() Determine whether this is a vacuous expression as defined in the XQuery update specification
SequenceIterator	iterate() Return an Iterator to iterate over the values of a sequence.
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
static Literal	makeEmptySequence() Factory method to make an empty-sequence literal
static Literal	makeLiteral(GroundedValue value) Factory method to create a literal as a wrapper around a Value (factory method)
static Literal	makeStringsLiteral(List<String> strings) Create a Literal containing a sequence of strings
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Optimize an expression
void	process(XPathContext context) Process the value as an instruction, without returning any tail calls
Expression	promote(PromotionOffer offer) Offer promotion for this subexpression.
Pattern	toPattern(Configuration config, boolean is30) Convert this expression to an equivalent XSLT pattern
String	toShortString() Produce a short string identifying the expression for use in error messages
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, ContextItemStaticInfo contextInfo) TypeCheck an expression

Methods inherited from class net.sf.saxon.expr.Expression

adoptChildExpression, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, clearStreamabilityData, computeDependencies, computeStaticProperties, doPromotion, dynamicError, explain, getCardinality, getConfiguration, getConstructType, getEvaluationMethod, getExpressionName, getHostLanguage, getIntrinsicDependencies, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getPosture, getPostureAndSweepIfKnown, getProperties, getProperty, getRetainedStaticContext, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStreamability, getSweep, getSystemId, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isCallOnSystemFunction, isIdentical, isUpdatingExpression, iterateEvents, makeStreamingAdjunct, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, optimizeForType, promoteChildren, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setFiltered, setFlattened, setLocation, setParentExpression, setPostureAndSweep, setRetainedStaticContext, setRetainedStaticContextLocally, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toStreamingPattern, typeCheckChildren, typeError, unordered

Methods inherited from class java.lang.Object

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

Constructor Detail

Literal

protected Literal(GroundedValue value)

Create a literal as a wrapper around a Value

Parameters:

value - the value of this literal

Method Detail

makeStringsLiteral

public static Literal makeStringsLiteral(List<String> strings)

Create a Literal containing a sequence of strings

Parameters:

strings - the strings to be wrapped

Returns:

a Literal of the string sequence

getValue

public GroundedValue getValue()

Get the value represented by this Literal

Returns:

the constant value

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                   ContextItemStaticInfo contextInfo)
                     throws XPathException

TypeCheck an expression

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

Returns:

for a Value, this always returns the value unchanged

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ContextItemStaticInfo contextItemType)
                    throws XPathException

Optimize an expression

Overrides:

optimize in class Expression

Parameters:

visitor - an expression visitor

contextItemType - 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 to Type.ITEM_TYPE

Returns:

for a Value, this always returns the value unchanged

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

getCost

public int getCost()

Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.

Overrides:

getCost in class Expression

Returns:

an estimate of the gross cost of evaluating the expression, including the cost of evaluating its operands.

getItemType

public ItemType getItemType()

Determine the data type of the items in the expression, if possible

Specified by:

getItemType in class Expression

Returns:

for the default implementation: AnyItemType (not known)

computeCardinality

public int computeCardinality()

Determine the cardinality

Specified by:

computeCardinality in class Expression

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

computeSpecialProperties

public int computeSpecialProperties()

Compute the static properties of this expression (other than its type). For a Value, the only special property is StaticProperty.NON_CREATIVE.

Overrides:

computeSpecialProperties in class Expression

Returns:

the value StaticProperty.NON_CREATIVE

getIntegerBounds

public IntegerValue[] getIntegerBounds()

For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.

Overrides:

getIntegerBounds in class Expression

Returns:

the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

isVacuousExpression

public boolean isVacuousExpression()

Determine whether this is a vacuous expression as defined in the XQuery update specification

Overrides:

isVacuousExpression in class Expression

Returns:

true if this expression is vacuous

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is accepted. This method is always called at compile time.

Overrides:

promote in class Expression

Parameters:

offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression

Returns:

if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws:

XPathException - if any error is detected

copy

public Expression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

a copy of the original literal. Note that the underlying value is not copied; the code relies on the caller treating the underlying value as immutable.

toPattern

public Pattern toPattern(Configuration config,
                boolean is30)
                  throws XPathException

Convert this expression to an equivalent XSLT pattern

Overrides:

toPattern in class Expression

Parameters:

config - the Saxon configuration

is30 - true if this is XSLT 3.0

Returns:

the equivalent pattern

Throws:

XPathException - if conversion is not possible

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 class Expression

Parameters:

pathMap - the PathMap to which the expression should be added

pathMapNodeSet - the set of nodes within the path map

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

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 class Expression

Returns:

for a Value, this always returns zero.

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.

Overrides:

iterate in class Expression

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

iterate

public SequenceIterator iterate()
                         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.

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

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.

Overrides:

evaluateItem in class Expression

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

process

public void process(XPathContext context)
             throws XPathException

Process the value as an instruction, without returning any tail calls

Overrides:

process in class Expression

Parameters:

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

Throws:

XPathException - if a dynamic error occurs

getImplementationMethod

public int getImplementationMethod()

Description copied from class: Expression

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.

Specified by:

getImplementationMethod in class Expression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

evaluateAsString

public 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 class Expression

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

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 class Expression

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

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 class Expression

Parameters:

context - the XPath dynamic evaluation context

pul - the pending update list to which the results should be written

Throws:

XPathException - if evaluation fails

equals

public boolean equals(Object obj)

Determine whether two literals are equal, when considered as expressions.

Overrides:

equals in class Object

Parameters:

obj - the other expression

Returns:

true if the two literals are equal. The test here requires (a) identity in the sense defined by XML Schema (same value in the same value space), and (b) identical type annotations. For example the literal xs:int(3) is not equal (as an expression) to xs:short(3), because the two expressions are not interchangeable.

hashCode

public int hashCode()

Return a hash code to support the equals() function

Overrides:

hashCode in class Object

toString

public 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 class Expression

Returns:

a representation of the expression as a string

export

public void export(ExpressionPresenter out)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in class Expression

Parameters:

out - the expression presenter used to display the structure

exportValue

public static void exportValue(Sequence value,
               ExpressionPresenter out)

exportAtomicValue

public static void exportAtomicValue(AtomicValue value,
                     ExpressionPresenter out)

toShortString

public String toShortString()

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class Expression

Returns:

a short string, sufficient to identify the expression

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:

true if the expression is a literal and the literal wraps an AtomicValue

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:

true if the expression is a literal and the value of the literal is an empty sequence

isConstantBoolean

public static boolean isConstantBoolean(Expression exp,
                        boolean value)

Test if a literal represents the boolean value true

Parameters:

exp - an expression

value - true or false

Returns:

true if the expression is a literal and the literal represents the boolean value given in the second argument

isConstantOne

public static boolean isConstantOne(Expression exp)

Test if a literal represents the integer value 1

Parameters:

exp - an expression

Returns:

true if the expression is a literal and the literal represents the integer value 1

isSubtreeExpression

public boolean isSubtreeExpression()

Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.

Overrides:

isSubtreeExpression in class Expression

Returns:

true if the expression has no dependencies on the context node, or if the only dependencies on the context node are downward selections using the self, child, descendant, attribute, and namespace axes.

makeEmptySequence

public static Literal makeEmptySequence()

Factory method to make an empty-sequence literal

Returns:

a literal whose value is the empty sequence

makeLiteral

public static Literal makeLiteral(GroundedValue value)

Factory method to create a literal as a wrapper around a Value (factory method)

Parameters:

value - the value of this literal

Returns:

the Literal

getStreamingAdjunct

protected StreamingAdjunct getStreamingAdjunct()

Description copied from class: Expression

Get an object that supports streamed evaluation of this expression

Overrides:

getStreamingAdjunct in class Expression

Returns:

the relevant StreamingAdjunct, or null if none is available

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the Literal expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler