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:

Serializable, SourceLocator, LocationProvider, SaxonLocator, ComparisonExpression, EvaluableItem, Negatable, SequenceIterable, InstructionInfo, Locator

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

See Also:

Serialized Form

Field Summary

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

operand0, operand1, operator

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

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

Method Summary

int	computeCardinality() Determine the static cardinality.
boolean	convertsUntypedToOther() Determine whether untyped atomic values should be converted to the type of the other operand
Expression	copy() Copy an expression.
boolean	effectiveBooleanValue(XPathContext context) Evaluate the effective boolean value of the expression
Item	evaluateItem(XPathContext context) Evaluate the expression in a given context
protected void	explainExtraAttribute(ExpressionPresenter out)
AtomicComparer	getAtomicComparer() Get the AtomicComparer used to compare atomic values.
String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
ItemType	getItemType(TypeHierarchy th) 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
boolean	isNegatable(ExpressionVisitor visitor) 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, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
void	setAtomicComparer(AtomicComparer comparer) Set the AtomicComparer used to compare atomic values
void	setResultWhenEmpty(BooleanValue value) Set the result to be returned if one of the operands is an empty sequence
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression

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

computeSpecialProperties, displayOperator, equals, explain, explainExtraAttributes, getOperands, getOperator, hashCode, isAssociative, isCommutative, isInverse, iterateSubExpressions, promote, replaceSubExpression, setFlattened, simplify, toString

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object

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

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

getOperands

Constructor Detail

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 Detail

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.

setAtomicComparer

public void setAtomicComparer(AtomicComparer comparer)

Set the AtomicComparer used to compare atomic values

Parameters:

comparer - the AtomicComparer

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

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

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,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression

Overrides:

typeCheck in class BinaryExpression

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:

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,
                           ItemType contextItemType)
                    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

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:

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(ExpressionVisitor visitor)

Check whether this specific instance of the expression is negatable

Specified by:

isNegatable in interface Negatable

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

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

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

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the expression in a given context

Specified by:

evaluateItem in interface EvaluableItem

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(TypeHierarchy th)

Determine the data type of the expression

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

Returns:

Type.BOOLEAN

computeCardinality

public 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

explainExtraAttribute

protected void explainExtraAttribute(ExpressionPresenter out)