net.sf.saxon.expr

Class ValueComparison

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
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 v1, int op, AtomicValue v2, AtomicComparer collator)
Compare two atomic values, using a specified operator and collation
intcomputeCardinality()
Determine the static cardinality.
protected StringdisplayOperator()
booleaneffectiveBooleanValue(XPathContext context)
Evaluate the effective boolean value of the expression
ItemevaluateItem(XPathContext context)
Evaluate the expression in a given context
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
ValueComparisonnegate()
Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false().
Expressionoptimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
voidsetResultWhenEmpty(BooleanValue value)
Set the result to be returned if one of the operands is an empty sequence
ExpressiontypeCheck(StaticContext env, 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 v1, int op, AtomicValue v2, AtomicComparer collator)
Compare two atomic values, using a specified operator and collation

Parameters: v1 the first operand op the operator, as defined by constants such as FEQ or FLT v2 the second operand collator the Collator to be used when comparing strings

Throws: net.sf.saxon.trans.DynamicError if the values are not comparable

computeCardinality

public int computeCardinality()
Determine the static cardinality.

displayOperator

protected String displayOperator()

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

getItemType

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

Parameters: th

Returns: Type.BOOLEAN

getResultWhenEmpty

public BooleanValue getResultWhenEmpty()
Get the result to be returned if one of the operands is an empty sequence

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 ().

optimize

public Expression optimize(Optimizer opt, StaticContext env, 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: 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 ITEM_TYPE

Returns: the original expression, rewritten if appropriate to optimize execution

Throws: net.sf.saxon.trans.StaticError if an error is discovered during this phase (typically a type error)

setResultWhenEmpty

public void setResultWhenEmpty(BooleanValue value)
Set the result to be returned if one of the operands is an empty sequence

typeCheck

public Expression typeCheck(StaticContext env, ItemType contextItemType)
Type-check the expression