net.sf.saxon.expr
Class IfExpression

java.lang.Object
  |
  +--net.sf.saxon.expr.ComputedExpression
        |
        +--net.sf.saxon.expr.IfExpression

All Implemented Interfaces:

Expression, Instr, Locatable, java.io.Serializable

public class IfExpression

extends ComputedExpression

implements Instr

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.
void	process(XPathContext context)           Process this expression as an instruction, writing results to the current outputter
TailCall	processLeavingTail(XPathContext context)           Process the instruction, optionally returning an uncompleted tail call to be invoked by the caller
Expression	promote(PromotionOffer offer)           Promote this expression if possible
Expression	simplify()           Simplify an expression

 

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

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

 

Methods inherited from class java.lang.Object

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

 

Methods inherited from interface net.sf.saxon.instruct.Locatable

getSourceLocator

 

Constructor Detail

IfExpression

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

Constructor

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

Specified by:

analyze in interface 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

XPathException

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

process

public void process(XPathContext context)
             throws javax.xml.transform.TransformerException

Process this expression as an instruction, writing results to the current outputter

Specified by:

process in interface Instr

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

javax.xml.transform.TransformerException

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws javax.xml.transform.TransformerException

Process the instruction, optionally returning an uncompleted tail call to be invoked by the caller

Specified by:

processLeavingTail in interface Instr

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

javax.xml.transform.TransformerException

getItemType

public ItemType getItemType()

Get data type of items in sequence returned by expression

Specified by:

getItemType in interface 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.

Overrides:

computeSpecialProperties in class ComputedExpression

display

public void display(int level,
                    NamePool pool)

Diagnostic print of expression structure

Specified by:

display in interface Expression

Parameters:

level - indentation level for this expression