net.sf.saxon.expr

Class IdentityComparison

Implemented Interfaces:
EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator

public final class IdentityComparison
extends BinaryExpression

IdentityComparison: a boolean expression that compares two nodes for equals, not-equals, greater-than or less-than based on identity and document ordering

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, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

IdentityComparison(Expression p1, int op, Expression p2)
Create an identity comparison identifying the two operands and the operator

Method Summary

Expression
copy()
Copy an expression.
boolean
effectiveBooleanValue(XPathContext context)
Get the effective boolean value of the expression.
Item
evaluateItem(XPathContext context)
Evaluate the expression
ItemType
getItemType(TypeHierarchy th)
Determine the data type of the expression
boolean
isGenerateIdEmulation()
Test the flag that indicates different empty-sequence behavior when emulating comparison of two generate-id's
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
void
setGenerateIdEmulation(boolean flag)
Set flag to indicate different empty-sequence behavior when emulating comparison of two generate-id's
Expression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

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

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

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Constructor Details

IdentityComparison

public IdentityComparison(Expression p1,
                          int op,
                          Expression p2)
Create an identity comparison 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

copy

public Expression copy()
Copy an expression. This makes a deep copy.
Overrides:
copy in interface Expression
Returns:
the copy of the original 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 interface 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

evaluateItem

public Item evaluateItem(XPathContext context)
            throws XPathException
Evaluate the expression
Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in interface Expression

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression
Overrides:
getItemType in interface Expression
Parameters:
th - the type hierarchy cache
Returns:
Type.BOOLEAN

isGenerateIdEmulation

public boolean isGenerateIdEmulation()
Test the flag that indicates different empty-sequence behavior when emulating comparison of two generate-id's
Returns:
true if this function is being used to compare generate-id() output

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 interface 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)

setGenerateIdEmulation

public void setGenerateIdEmulation(boolean flag)
Set flag to indicate different empty-sequence behavior when emulating comparison of two generate-id's
Parameters:
flag - true if this function is being used to compare generate-id() output

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
            throws XPathException
Type-check the expression
Overrides:
typeCheck in interface BinaryExpression