net.sf.saxon.expr
Class IfExpression

java.lang.Object
  |
  +--net.sf.saxon.expr.ComputedExpression
        |
        +--net.sf.saxon.expr.IfExpression
All Implemented Interfaces:
Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

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
locationId, staticProperties
 
Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
IfExpression(Expression condition, Expression thenExp, Expression elseExp)
          Constructor
 
Method Summary
 Expression analyze(StaticContext env, ItemType contextItemType)
          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, java.io.PrintStream out)
          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
 SequenceIterator iterate(XPathContext context)
          Iterate the path-expression in a given context
 java.util.Iterator iterateSubExpressions()
          Get the immediate subexpressions of this expression
 boolean markTailFunctionCalls()
          Mark tail calls on used-defined functions.
 void process(XPathContext context)
          Process this expression as an instruction, writing results to the current receiver
 Expression promote(PromotionOffer offer)
          Promote this expression if possible
 Expression simplify(StaticContext env)
          Simplify an expression
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, computeDependencies, computeStaticProperties, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getParentExpression, getPublicId, getSpecialProperties, getSystemId, resetStaticProperties, setLocationId, setParentExpression, 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(StaticContext env)
                    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,
                          ItemType contextItemType)
                   throws XPathException
Type-check the expression

Parameters:
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 Type.ITEM_TYPE
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

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()
Get the immediate subexpressions of this expression

Specified by:
iterateSubExpressions in interface Expression
Overrides:
iterateSubExpressions in class ComputedExpression
Returns:
an iterator 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 XPathException
Process this expression as an instruction, writing results to the current receiver

Specified by:
process in interface Expression
Overrides:
process in class ComputedExpression
Parameters:
context - The dynamic context, giving access to the current node, the current variables, etc.
XPathException

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.

Overrides:
computeSpecialProperties in class ComputedExpression

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)
Diagnostic print of expression structure

Parameters:
level - indentation level for this expression
pool - NamePool used to expand any names appearing in the expression
out - Output destination