net.sf.saxon.expr
Class ValueComparison

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.BinaryExpression
          net.sf.saxon.expr.ValueComparison

All Implemented Interfaces:

Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

public final class ValueComparison

extends BinaryExpression

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.ComputedExpression

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

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

Method Summary

int	computeCardinality() Determine the static cardinality.
protected java.lang.String	displayOperator()
boolean	effectiveBooleanValue(XPathContext context) Evaluate the effective boolean value of the expression
Item	evaluateItem(XPathContext context) Evaluate the expression in a given context
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
ValueComparison	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(Optimizer opt, StaticContext env, ItemType contextItemType) 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
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression

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

computeSpecialProperties, display, equals, getOperands, getOperator, hashCode, isAssociative, isCommutative, isInverse, iterateSubExpressions, promote, simplify

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

ValueComparison

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

Create a relational 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

setResultWhenEmpty

public void setResultWhenEmpty(BooleanValue value)

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

getResultWhenEmpty

public BooleanValue getResultWhenEmpty()

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

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression

Specified by:

typeCheck in interface Expression

Overrides:

typeCheck in class BinaryExpression

Throws:

XPathException

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           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.

Specified by:

optimize in interface Expression

Overrides:

optimize in class BinaryExpression

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

env - the static context of the expression

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:

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

XPathException

negate

public ValueComparison 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 ().

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException

Evaluate the effective boolean value of the expression

Specified by:

effectiveBooleanValue in interface Expression

Overrides:

effectiveBooleanValue in class ComputedExpression

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 Expression

Overrides:

evaluateItem in class ComputedExpression

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

Parameters:

th -

Returns:

Type.BOOLEAN

computeCardinality

public int computeCardinality()

Determine the static cardinality.

Overrides:

computeCardinality in class BinaryExpression

displayOperator

protected java.lang.String displayOperator()

Overrides:

displayOperator in class BinaryExpression