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, ComparisonExpression, Container, EvaluableItem, SequenceIterable, InstructionInfoProvider

public final class ValueComparison
extends BinaryExpression
implements ComparisonExpression

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.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.
boolean	convertsUntypedToOther() Determine whether untyped atomic values should be converted to the type of the other operand
boolean	effectiveBooleanValue(XPathContext context) Evaluate the effective boolean value of the expression
Item	evaluateItem(XPathContext context) Evaluate the expression in a given context
AtomicComparer	getAtomicComparer() Get the AtomicComparer used to compare atomic values.
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
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, iterateSubExpressions, promote, replaceSubExpression, simplify

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

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

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, 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 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

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

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

Overrides:

typeCheck in class BinaryExpression

Parameters:

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 to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

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

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.

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

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 -

Returns:

Type.BOOLEAN

computeCardinality

public int computeCardinality()

Determine the static cardinality.

Overrides:

computeCardinality in class BinaryExpression