net.sf.saxon.expr
Class Literal

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.Literal

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, 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

Field Summary

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

EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD

Constructor Summary

Literal(Value value)
Create a literal as a wrapper around a Value

Method Summary

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	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 possible
Value	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(XPathContext context) Return an Iterator to iterate over the values of a sequence.
static Literal	makeEmptySequence() Make an empty-sequence literal
static Literal	makeLiteral(Value value) Create a literal as a wrapper around a Value (factory method)
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Optimize an expression
void	process(XPathContext context) Process the value as an instruction, without returning any tail calls
Expression	simplify(ExpressionVisitor visitor) Simplify an expression
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, doPromotion, dynamicError, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getEvaluationMethod, getExecutable, getExpressionName, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, iterateSameFocusSubExpressions, iterateSubExpressions, markTailFunctionCalls, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

Literal

public Literal(Value value)

Create a literal as a wrapper around a Value

Parameters:

value - the value of this literal

Method Detail

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

makeEmptySequence

public static Literal makeEmptySequence()

Make an empty-sequence literal

Returns:

a literal whose value is the empty sequence

getValue

public Value getValue()

Get the value represented by this Literal

Returns:

the constant value

simplify

public Expression simplify(ExpressionVisitor visitor)

Simplify an expression

Overrides:

simplify in class Expression

Parameters:

visitor - an expression visitor

Returns:

for a Value, this always returns the value unchanged

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)

TypeCheck an expression

Overrides:

typeCheck 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

optimize

public final Expression optimize(ExpressionVisitor visitor,
                                 ItemType contextItemType)

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

getItemType

public ItemType getItemType(TypeHierarchy th)

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

Specified by:

getItemType in class Expression

Parameters:

th - The TypeHierarchy. Can be null if the target is an AtomicValue.

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

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

copy

public Expression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

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 -

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.

Specified by:

iterate in interface SequenceIterable

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

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 interface EvaluableItem

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

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

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

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 class Expression

Parameters:

out - the expression presenter used to display the structure

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

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

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:

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:

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.