net.sf.saxon.expr
Class ValueComparison

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.BinaryExpression
          extended by net.sf.saxon.expr.ValueComparison
All Implemented Interfaces:
Serializable, SourceLocator, ComparisonExpression, EvaluableItem, Negatable, SequenceIterable, InstructionInfoProvider

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.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
 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
 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
 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 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, equals, explain, getOperands, getOperator, hashCode, iterateSubExpressions, promote, replaceSubExpression, setFlattened, simplify, toString
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, evaluateAsString, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
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 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

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


Copyright (C) Michael H. Kay. All rights reserved.