Package net.sf.saxon.expr
Class FirstItemExpression
java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.UnaryExpression
net.sf.saxon.expr.SingleItemFilter
net.sf.saxon.expr.FirstItemExpression
- All Implemented Interfaces:
Serializable
,SourceLocator
,LocationProvider
,SaxonLocator
,InstructionInfo
,Locator
A FirstItemExpression returns the first item in the sequence returned by a given
base expression
- See Also:
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Field Summary
Fields inherited from class net.sf.saxon.expr.UnaryExpression
operand
Fields inherited from class net.sf.saxon.expr.Expression
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD
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Method Summary
Modifier and TypeMethodDescriptioncopy()
Copy an expression.evaluateItem
(XPathContext context) Evaluate the expressionGet a name identifying the kind of expression, in terms meaningful to a user.static Expression
Static factory methodMethods inherited from class net.sf.saxon.expr.SingleItemFilter
computeCardinality, optimize, promote
Methods inherited from class net.sf.saxon.expr.UnaryExpression
computeSpecialProperties, displayOperator, equals, explain, getBaseExpression, getItemType, hashCode, iterateSubExpressions, replaceSubExpression, simplify, toString, typeCheck
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError
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Method Details
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makeFirstItemExpression
Static factory method- Parameters:
base
- A sequence expression denoting sequence whose first item is to be returned- Returns:
- the FirstItemExpression, or an equivalent
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copy
Copy an expression. This makes a deep copy.- Specified by:
copy
in classExpression
- Returns:
- the copy of the original expression
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evaluateItem
Evaluate the expression- Overrides:
evaluateItem
in classExpression
- Parameters:
context
- The context in which the expression is to be evaluated- 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
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getExpressionName
Description copied from class:Expression
Get a name identifying the kind of expression, in terms meaningful to a user.- Overrides:
getExpressionName
in classExpression
- Returns:
- a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.
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