net.sf.saxon.expr

Class ValueComparison

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
Constructor Summary
ValueComparison(Expression p1, int op, Expression p2)
Create a relational expression identifying the two operands and the operator
Method Summary
static booleancompare(AtomicValue v0, int op, AtomicValue v1, AtomicComparer collator, boolean checkTypes)
Compare two atomic values, using a specified operator and collation
intcomputeCardinality()
Determine the static cardinality.
booleanconvertsUntypedToOther()
Determine whether untyped atomic values should be converted to the type of the other operand
Expressioncopy()
Copy an expression.
booleaneffectiveBooleanValue(XPathContext context)
Evaluate the effective boolean value of the expression
ItemevaluateItem(XPathContext context)
Evaluate the expression in a given context
protected voidexplainExtraAttribute(ExpressionPresenter out)
AtomicComparergetAtomicComparer()
Get the AtomicComparer used to compare atomic values.
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the expression
BooleanValuegetResultWhenEmpty()
Get the result to be returned if one of the operands is an empty sequence
intgetSingletonOperator()
Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE
booleanisNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable
booleanneedsRuntimeComparabilityCheck()
Determine whether a run-time check is needed to check that the types of the arguments are comparable
Expressionnegate()
Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false().
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
voidsetAtomicComparer(AtomicComparer comparer)
Set the AtomicComparer used to compare atomic values
voidsetResultWhenEmpty(BooleanValue value)
Set the result to be returned if one of the operands is an empty sequence
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

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

compare

static boolean compare(AtomicValue v0, int op, AtomicValue v1, AtomicComparer collator, boolean checkTypes)
Compare two atomic values, using a specified operator and collation

Parameters: v0 the first operand op the operator, as defined by constants such as FEQ or FLT v1 the second operand collator the Collator to be used when comparing strings checkTypes

Returns: the result of the comparison: -1 for LT, 0 for EQ, +1 for GT

Throws: XPathException if the values are not comparable

computeCardinality

public int computeCardinality()
Determine the static cardinality.

convertsUntypedToOther

public boolean convertsUntypedToOther()
Determine whether untyped atomic values should be converted to the type of the other operand

Returns: true if untyped values should be converted to the type of the other operand, false if they should be converted to strings.

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
Evaluate the effective boolean value of the expression

Parameters: context the given context for evaluation

Returns: a boolean representing the result of the comparison of the two operands

evaluateItem

public Item evaluateItem(XPathContext context)
Evaluate the expression in a given context

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

explainExtraAttribute

protected void explainExtraAttribute(ExpressionPresenter out)

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.

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression

Parameters: th the type hierarchy cache

Returns: Type.BOOLEAN

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)

getSingletonOperator

public int getSingletonOperator()
Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE

isNegatable

public boolean isNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable

Returns: true if it is

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

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 ().

Returns: the inverted comparison

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
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.

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 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)

setAtomicComparer

public void setAtomicComparer(AtomicComparer comparer)
Set the AtomicComparer used to compare atomic values

Parameters: comparer the AtomicComparer

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.

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression