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:

IdentityComparable

public final class FirstItemExpression
extends SingleItemFilter

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.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Method Summary

Methods

Modifier and Type	Method and Description
Expression	copy() Copy an expression.
Item	evaluateItem(XPathContext context) Evaluate the expression
ExpressionCompiler	getExpressionCompiler() Return the compiler of the FirstItem expression
String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
FirstItemExpressionAdjunct	getStreamingAdjunct() Get an object that supports streamed evaluation of this expression
static Expression	makeFirstItemExpression(Expression base) Static factory method
Pattern	toPattern(Configuration config, boolean is30) Convert this expression to an equivalent XSLT pattern
String	toShortString() Produce a short string identifying the expression for use in error messages

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

computeCardinality, getOperandRole, optimize

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

computeSpecialProperties, displayOperator, equals, export, getBaseExpression, getItemType, getOperand, hashCode, operands, setBaseExpression, toString, typeCheck

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

addToPathMap, adoptChildExpression, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, clearStreamabilityData, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getDependencies, getEvaluationMethod, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getPosture, getPostureAndSweepIfKnown, getProperties, getProperty, getRetainedStaticContext, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStreamability, getSweep, getSystemId, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isCallOnSystemFunction, isIdentical, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, makeStreamingAdjunct, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, optimizeForType, process, promote, promoteChildren, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setFiltered, setFlattened, setLocation, setParentExpression, setPostureAndSweep, setRetainedStaticContext, setRetainedStaticContextLocally, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toStreamingPattern, typeCheckChildren, typeError, unordered

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Method Detail

makeFirstItemExpression

public static Expression makeFirstItemExpression(Expression base)

Static factory method

Parameters:

base - A sequence expression denoting sequence whose first item is to be returned

Returns:

the FirstItemExpression, or an equivalent

copy

public Expression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

toPattern

public Pattern toPattern(Configuration config,
                boolean is30)
                  throws XPathException

Convert this expression to an equivalent XSLT pattern

Overrides:

toPattern in class Expression

Parameters:

config - the Saxon configuration

is30 - true if this is XSLT 3.0

Returns:

the equivalent pattern

Throws:

XPathException - if conversion is not possible

getImplementationMethod

public int getImplementationMethod()

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.

Specified by:

getImplementationMethod in class Expression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the expression

Overrides:

evaluateItem in class Expression

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

getExpressionName

public String getExpressionName()

Description copied from class: Expression

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Expression

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 export() output displaying the expression.

toShortString

public String toShortString()

Description copied from class: Expression

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class UnaryExpression

Returns:

a short string, sufficient to identify the expression

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the FirstItem expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler

getStreamingAdjunct

public FirstItemExpressionAdjunct getStreamingAdjunct()

Description copied from class: Expression

Get an object that supports streamed evaluation of this expression

Overrides:

getStreamingAdjunct in class Expression

Returns:

the relevant StreamingAdjunct, or null if none is available