net.sf.saxon.expr
Class IfExpression

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.IfExpression

All Implemented Interfaces:

Serializable, Expression

public class IfExpression
extends ComputedExpression

An IfExpression returns the value of either the "then" part or the "else" part, depending on the value of the condition

See Also:

Serialized Form

Field Summary

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

lineNumber, NO_ARGUMENTS, staticProperties

Constructor Summary

IfExpression(Expression condition, Expression thenExp, Expression elseExp)
Constructor

Method Summary

Expression	analyze(StaticContext env) Type-check the expression
int	computeCardinality() Determine the static cardinality of the result
int	ComputeSpecialProperties() Get the static properties of this expression (other than its type).
void	display(int level, NamePool pool) Diagnostic print of expression structure
Item	evaluateItem(XPathContext context) Evaluate the conditional expression in a given context
ItemType	getItemType() Get data type of items in sequence returned by expression
Expression[]	getSubExpressions() Get the immediate subexpressions of this expression
SequenceIterator	iterate(XPathContext context) Iterate the path-expression in a given context
boolean	markTailFunctionCalls() Mark tail calls on used-defined functions.
Expression	promote(PromotionOffer offer) Promote this expression if possible
Expression	simplify() Simplify an expression

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

computeDependencies, computeSpecialProperties, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getDependencies, getIntrinsicDependencies, getLineNumber, getSpecialProperties, setLineNumber, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

IfExpression

public IfExpression(Expression condition,
                    Expression thenExp,
                    Expression elseExp)

Constructor

Method Detail

simplify

public Expression simplify()
                    throws XPathException

Simplify an expression

Specified by:

simplify in interface Expression

Overrides:

simplify in class ComputedExpression

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

analyze

public Expression analyze(StaticContext env)
                   throws XPathException

Type-check the expression

Parameters:

env - the static context of the expression

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)

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

Specified by:

promote in interface Expression

Overrides:

promote in class ComputedExpression

Parameters:

offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression

Returns:

if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws:

XPathException - if any error is detected

getSubExpressions

public Expression[] getSubExpressions()

Get the immediate subexpressions of this expression

Specified by:

getSubExpressions in interface Expression

Overrides:

getSubExpressions in class ComputedExpression

Returns:

an array containing the sub-expressions of this expression

markTailFunctionCalls

public boolean markTailFunctionCalls()

Mark tail calls on used-defined functions. For most expressions, this does nothing.

Overrides:

markTailFunctionCalls in class ComputedExpression

Returns:

true if a tail recursive call was found and if this call accounts for the whole of the value.

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the conditional expression in a given context

Specified by:

evaluateItem in interface Expression

Overrides:

evaluateItem in class ComputedExpression

Parameters:

context - the evaluation context

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate the path-expression in a given context

Specified by:

iterate in interface Expression

Overrides:

iterate in class ComputedExpression

Parameters:

context - the evaluation context

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

Throws:

XPathException - if any dynamic error occurs evaluating the expression

getItemType

public ItemType getItemType()

Get data type of items in sequence returned by expression

Returns:

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

computeCardinality

public int computeCardinality()

Determine the static cardinality of the result

Specified by:

computeCardinality in class ComputedExpression

ComputeSpecialProperties

public int ComputeSpecialProperties()

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

display

public void display(int level,
                    NamePool pool)

Diagnostic print of expression structure

Parameters:

level - indentation level for this expression