Package net.sf.saxon.expr

Class ValueComparison

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.BinaryExpression

net.sf.saxon.expr.ValueComparison

All Implemented Interfaces:

ComparisonExpression, ExportAgent, Locatable, Negatable, IdentityComparable, Traceable

public final class ValueComparison
extends BinaryExpression
implements ComparisonExpression, Negatable

ValueComparison: a boolean expression that compares two atomic values for equals, not-equals, greater-than or less-than. Implements the operators eq, ne, lt, le, gt, ge

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ValueComparison.ValueComparisonElaborator	Elaborator for a value comparison (such as A eq B), including the case where a general comparison is reduced to a value comparison by the optimiser

Field Summary

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

operator

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

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

Constructor Summary

Constructors

Constructor	Description
ValueComparison(Expression p1, int op, Expression p2)	Create a comparison expression identifying the two operands and the operator

Method Summary

Modifier and Type	Method	Description
static boolean	compare(AtomicValue v0, int op, AtomicValue v1, AtomicComparer comparer, boolean checkTypes)	Compare two atomic values, using a specified operator and collation
protected int	computeCardinality()	Determine the static cardinality.
protected int	computeHashCode()	Get a hashCode for comparing two expressions.
boolean	convertsUntypedToOther()	Determine whether untyped atomic values should be converted to the type of the other operand
Expression	copy(RebindingMap rebindings)	Copy an expression.
boolean	effectiveBooleanValue(XPathContext context)	Evaluate the effective boolean value of the expression
boolean	equals(Object other)	Is this expression the same as another expression?
BooleanValue	evaluateItem(XPathContext context)	Evaluate the expression in a given context
protected void	explainExtraAttributes(ExpressionPresenter out)	Add subclass-specific attributes to the expression tree explanation.
AtomicComparer	getAtomicComparer()	Get the AtomicComparer used to compare atomic values.
Elaborator	getElaborator()	Make an elaborator for this expression
String	getExpressionName()	Get a name identifying the kind of expression, in terms meaningful to a user.
ItemType	getItemType()	Determine the data type of the expression
BooleanValue	getResultWhenEmpty()	Get the result to be returned if one of the operands is an empty sequence
int	getSingletonOperator()	Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE
UType	getStaticUType(UType contextItemType)	Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
StringCollator	getStringCollator()	Get the StringCollator used to compare string values.
boolean	isNegatable(TypeHierarchy th)	Check whether this specific instance of the expression is negatable
boolean	needsRuntimeComparabilityCheck()	Determine whether a run-time check is needed to check that the types of the arguments are comparable
Expression	negate()	Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false().
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)	Perform optimisation of an expression and its subexpressions.
void	setResultWhenEmpty(BooleanValue value)	Set the result to be returned if one of the operands is an empty sequence
protected String	tag()	Get the element name used to identify this expression in exported expression format
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)	Type-check the expression

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

computeSpecialProperties, displayOperator, export, getImplementationMethod, getLhs, getLhsExpression, getOperandRole, getOperator, getRhs, getRhsExpression, isAssociative, isCommutative, isInverse, operands, setFlattened, setLhsExpression, setRhsExpression, toShortString, toString

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

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dispatchTailCall, dynamicError, evaluateAsString, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStreamerName, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, makeElaborator, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, supportsLazyEvaluation, suppressValidation, toPattern, typeCheckChildren, typeError, unordered, verifyParentPointers, withLocation

Methods inherited from class java.lang.Object

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

Methods inherited from interface net.sf.saxon.expr.ComparisonExpression

getLhs, getLhsExpression, getRhs, getRhsExpression

Methods inherited from interface net.sf.saxon.trace.Traceable

gatherProperties

Constructor Details

ValueComparison

public ValueComparison(Expression p1,
 int op,
 Expression p2)

Create a comparison expression identifying the two operands and the operator

Parameters:

p1 - the left-hand operand

op - the operator, as a token returned by the Tokenizer (e.g. Token.LT)

p2 - the right-hand operand

Method Details

getExpressionName

public String getExpressionName()

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Expression

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

getAtomicComparer

public AtomicComparer getAtomicComparer()

Get the AtomicComparer used to compare atomic values. This encapsulates any collation that is used. Note that the comparer is always known at compile time.

Specified by:

getAtomicComparer in interface ComparisonExpression

Returns:

the comparer

getStringCollator

public StringCollator getStringCollator()

Get the StringCollator used to compare string values.

Specified by:

getStringCollator in interface ComparisonExpression

Returns:

the collator. May return null if the expression will never be used to compare strings

getSingletonOperator

public int getSingletonOperator()

Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE

Specified by:

getSingletonOperator in interface ComparisonExpression

Returns:

the operator, as defined in class Token

convertsUntypedToOther

public boolean convertsUntypedToOther()

Determine whether untyped atomic values should be converted to the type of the other operand

Specified by:

convertsUntypedToOther in interface ComparisonExpression

Returns:

true if untyped values should be converted to the type of the other operand, false if they should be converted to strings.

setResultWhenEmpty

public void setResultWhenEmpty(BooleanValue value)

Set the result to be returned if one of the operands is an empty sequence

Parameters:

value - the result to be returned if an operand is empty. Supply null to mean the empty sequence.

getResultWhenEmpty

public BooleanValue getResultWhenEmpty()

Get the result to be returned if one of the operands is an empty sequence

Returns:

BooleanValue.TRUE, BooleanValue.FALSE, or null (meaning the empty sequence)

needsRuntimeComparabilityCheck

public boolean needsRuntimeComparabilityCheck()

Determine whether a run-time check is needed to check that the types of the arguments are comparable

Returns:

true if a run-time check is needed

typeCheck

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

Type-check the expression

Overrides:

typeCheck in class BinaryExpression

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:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

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

optimize

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

Perform optimisation of an expression and its subexpressions.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:

optimize in class BinaryExpression

Parameters:

visitor - an expression visitor

contextInfo - 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:

the original expression, rewritten if appropriate to optimize execution

Throws:

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

isNegatable

public boolean isNegatable(TypeHierarchy th)

Check whether this specific instance of the expression is negatable

Specified by:

isNegatable in interface Negatable

Parameters:

th - the type hierarchy

Returns:

true if it is

negate

public Expression negate()

Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false(). The result must be the same as not(this) even in the case where one of the operands is ().

Specified by:

negate in interface Negatable

Returns:

the inverted comparison

equals

public boolean equals(Object other)

Description copied from class: BinaryExpression

Is this expression the same as another expression?

Overrides:

equals in class BinaryExpression

Parameters:

other - the other operand; the result is false if this is not an Expression

Returns:

true if the other operand is an expression and if it can be determined that the two expressions are equivalent, in the sense that they will always return the same result.

computeHashCode

protected int computeHashCode()

Get a hashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.

Overrides:

computeHashCode in class BinaryExpression

Returns:

a computed hash code

copy

public Expression copy(RebindingMap rebindings)

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings - variables that need to be re-bound

Returns:

the copy of the original expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException

Evaluate the effective boolean value of the expression

Overrides:

effectiveBooleanValue in class Expression

Parameters:

context - the given context for evaluation

Returns:

a boolean representing the result of the comparison of the two operands

Throws:

XPathException - if any dynamic error occurs evaluating the expression

compare

public static boolean compare(AtomicValue v0,
 int op,
 AtomicValue v1,
 AtomicComparer comparer,
 boolean checkTypes)
                       throws XPathException

Compare two atomic values, using a specified operator and collation

Parameters:

v0 - the first operand

op - the operator, as defined by constants such as Token.FEQ or Token.FLT

v1 - the second operand

comparer - used to compare values. If the comparer is context-sensitive then the context must already have been bound using comparer.provideContext().

checkTypes - set to true if it is necessary to check that the types of the arguments are comparable

Returns:

the result of the comparison: -1 for LT, 0 for EQ, +1 for GT

Throws:

XPathException - if the values are not comparable

evaluateItem

public BooleanValue evaluateItem(XPathContext context)
                          throws XPathException

Evaluate the expression in a given context

Overrides:

evaluateItem in class Expression

Parameters:

context - the given context for evaluation

Returns:

a BooleanValue representing the result of the numeric comparison of the two operands, or null representing the empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

getItemType

public ItemType getItemType()

Determine the data type of the expression

Specified by:

getItemType in class Expression

Returns:

Type.BOOLEAN

getStaticUType

public UType getStaticUType(UType contextItemType)

Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.

Overrides:

getStaticUType in class Expression

Parameters:

contextItemType - the static type of the context item

Returns:

the static item type of the expression according to the XSLT 3.0 defined rules

computeCardinality

protected int computeCardinality()

Determine the static cardinality.

Overrides:

computeCardinality in class BinaryExpression

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. May also return StaticProperty.ALLOWS_ZERO if the result is known to be an empty sequence, or StaticProperty.ALLOWS_MANY if if is known to return a sequence of length two or more.

tag

protected String tag()

Description copied from class: BinaryExpression

Get the element name used to identify this expression in exported expression format

Overrides:

tag in class BinaryExpression

Returns:

the element name used to identify this expression

explainExtraAttributes

protected void explainExtraAttributes(ExpressionPresenter out)

Description copied from class: BinaryExpression

Add subclass-specific attributes to the expression tree explanation. Default implementation does nothing; this is provided for subclasses to override.

Overrides:

explainExtraAttributes in class BinaryExpression

Parameters:

out - the output destination for the displayed expression tree

getElaborator

public Elaborator getElaborator()

Make an elaborator for this expression

Overrides:

getElaborator in class Expression

Returns:

a suitable elaborator