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java.lang.Object | +--net.sf.saxon.expr.ComputedExpression | +--net.sf.saxon.expr.UnaryExpression | +--net.sf.saxon.expr.FirstItemExpression
A FirstItemExpression returns the first item in the sequence returned by a given base expression
Field Summary |
Fields inherited from class net.sf.saxon.expr.UnaryExpression |
operand |
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 | |
FirstItemExpression(Expression base)
Constructor |
Method Summary | |
Expression |
analyze(StaticContext env,
ItemType contextItemType)
Type-check the expression |
int |
computeCardinality()
Get the static cardinality |
java.lang.String |
displayOperator(NamePool pool)
Diagnostic print of expression structure |
Item |
evaluateItem(XPathContext context)
Evaluate the expression |
Expression |
promote(PromotionOffer offer)
Promote this expression if possible |
Methods inherited from class net.sf.saxon.expr.UnaryExpression |
computeSpecialProperties, display, equals, getBaseExpression, getItemType, hashCode, iterateSubExpressions, simplify |
Methods inherited from class java.lang.Object |
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
public FirstItemExpression(Expression base)
base
- A sequence expression denoting sequence whose first item is to be returnedMethod Detail |
public Expression analyze(StaticContext env, ItemType contextItemType) throws XPathException
analyze
in interface Expression
analyze
in class UnaryExpression
env
- the static context of the expressioncontextItemType
- 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
XPathException
public Expression promote(PromotionOffer offer) throws XPathException
promote
in interface Expression
promote
in class UnaryExpression
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
XPathException
- if any error is detectedpublic int computeCardinality()
computeCardinality
in class UnaryExpression
public Item evaluateItem(XPathContext context) throws XPathException
evaluateItem
in interface Expression
evaluateItem
in class ComputedExpression
context
- The context in which the expression is to be evaluated
XPathException
- if any dynamic error occurs evaluating the
expressionpublic java.lang.String displayOperator(NamePool pool)
displayOperator
in class UnaryExpression
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