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java.lang.Objectnet.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 | |
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 |
optimize(Optimizer opt,
StaticContext env,
ItemType contextItemType)
Perform optimisation of an expression and its subexpressions. |
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, typeCheck |
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 optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException
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.
optimize
in interface Expression
optimize
in class UnaryExpression
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 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
StaticError
- if an error is discovered during this phase
(typically a type error)
XPathException
public Expression promote(PromotionOffer offer) throws XPathException
promote
in interface Expression
promote
in class UnaryExpression
XPathException
public 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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