net.sf.saxon.expr

Class RootExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.RootExpression

All Implemented Interfaces:

ExportAgent, Locatable, IdentityComparable

public class RootExpression
extends Expression

An expression whose value is always a set of nodes containing a single node, the document root. This corresponds to the XPath Expression "/", including the implicit "/" at the start of a path expression with a leading "/".

Field Summary

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

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

Constructor Summary

Constructors

Constructor and Description
RootExpression()

Method Summary

Modifier and Type	Method and Description
PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
int	computeCardinality() Specify that the expression returns a singleton
int	computeHashCode() get HashCode for comparing two expressions
int	computeSpecialProperties() Compute the special properties of this expression.
Expression	copy(RebindingMap rebindings) Copy an expression.
boolean	effectiveBooleanValue(XPathContext context) Get the effective boolean value of the expression.
boolean	equals(java.lang.Object other) Is this expression the same as another expression?
NodeInfo	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	export(ExpressionPresenter destination) Diagnostic print of expression structure.
java.lang.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().
int	getIntrinsicDependencies() Determine which aspects of the context the expression depends on.
ItemType	getItemType() Determine the data type of the items returned by this expression
NodeInfo	getNode(XPathContext context) Return the first element selected by this Expression
UType	getStaticUType(UType contextItemType) Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
java.lang.String	getStreamerName() Get the (partial) name of a class that supports streaming of this kind of expression
boolean	isContextPossiblyUndefined() Ask whether there is a possibility that the context item will be undefined
SequenceIterator<?>	iterate(XPathContext context) Evaluate the expression in a given context to return an iterator
protected java.lang.String	noContextMessage() Customize the error message on type checking
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Perform optimisation of an expression and its subexpressions.
Pattern	toPattern(Configuration config) Convert this expression to an equivalent XSLT pattern
java.lang.String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Type-check the expression.

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

adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toShortString, typeCheckChildren, typeError, unordered, verifyParentPointers

Methods inherited from class java.lang.Object

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

Constructor Detail

RootExpression

public RootExpression()

Method Detail

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ContextItemStaticInfo contextInfo)
                     throws XPathException

Type-check the expression.

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ContextItemStaticInfo contextItemType)
                    throws XPathException

Perform optimisation of an expression and its subexpressions.

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.

Overrides:

optimize in class Expression

Parameters:

visitor - an expression visitor

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 if appropriate to optimize execution

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

computeSpecialProperties

public int computeSpecialProperties()

Description copied from class: Expression

Compute the special properties of this expression. These properties are denoted by a bit-significant integer, possible values are in class StaticProperty. The "special" properties are properties other than cardinality and dependencies, and most of them relate to properties of node sequences, for example whether the nodes are in document order.

Overrides:

computeSpecialProperties in class Expression

Returns:

the special properties, as a bit-significant integer

isContextPossiblyUndefined

public boolean isContextPossiblyUndefined()

Ask whether there is a possibility that the context item will be undefined

Returns:

true if this is a possibility

noContextMessage

protected java.lang.String noContextMessage()

Customize the error message on type checking

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

Overrides:

equals in class Expression

Parameters:

other - the other operand; the result is false if this is not an Expression

Returns:

true if the other operand is an expression and if it can be determined that the two expressions are equivalent, in the sense that they will always return the same result.

computeCardinality

public final int computeCardinality()

Specify that the expression returns a singleton

Specified by:

computeCardinality in class Expression

Returns:

the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE. May also return StaticProperty.ALLOWS_ZERO if the result is known to be an empty sequence, or StaticProperty.ALLOWS_MANY if if is known to return a sequence of length two or more.

getItemType

public ItemType getItemType()

Determine the data type of the items returned by this expression

Specified by:

getItemType in class Expression

Returns:

Type.NODE

getStaticUType

public UType getStaticUType(UType contextItemType)

Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.

Overrides:

getStaticUType in class Expression

Parameters:

contextItemType -

Returns:

the static item type of the expression according to the XSLT 3.0 defined rules

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

computeHashCode

public int computeHashCode()

get HashCode for comparing two expressions

Overrides:

computeHashCode in class Expression

Returns:

a computed hash code

getNode

public NodeInfo getNode(XPathContext context)
                 throws XPathException

Return the first element selected by this Expression

Parameters:

context - The evaluation context

Returns:

the NodeInfo of the first selected element, or null if no element is selected

Throws:

XPathException

getIntrinsicDependencies

public int getIntrinsicDependencies()

Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.VARIABLES and StaticProperty.CURRENT_NODE

Overrides:

getIntrinsicDependencies in class Expression

Returns:

a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

copy

public Expression copy(RebindingMap rebindings)

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings -

Returns:

the copy of the original expression

toPattern

public Pattern toPattern(Configuration config)
                  throws XPathException

Convert this expression to an equivalent XSLT pattern

Overrides:

toPattern in class Expression

Parameters:

config - the Saxon configuration

Returns:

the equivalent pattern

Throws:

XPathException - if conversion is not possible

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                           PathMap.PathMapNodeSet pathMapNodeSet)

Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

Overrides:

addToPathMap in class Expression

Parameters:

pathMap - the PathMap to which the expression should be added

pathMapNodeSet -

Returns:

the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

toString

public java.lang.String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:

toString in class Expression

Returns:

a representation of the expression as a string

getExpressionName

public java.lang.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.

export

public void export(ExpressionPresenter destination)
            throws XPathException

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in interface ExportAgent

Specified by:

export in class Expression

Parameters:

destination - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

iterate

public SequenceIterator<?> iterate(XPathContext context)
                            throws XPathException

Evaluate the expression in a given context to return an iterator

Overrides:

iterate in class Expression

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

evaluateItem

public NodeInfo evaluateItem(XPathContext context)
                      throws XPathException

Description copied from class: Expression

Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException

Description copied from class: Expression

Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Overrides:

effectiveBooleanValue in class Expression

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the effective boolean value

Throws:

XPathException - if any dynamic error occurs evaluating the expression

getStreamerName

public java.lang.String getStreamerName()

Get the (partial) name of a class that supports streaming of this kind of expression

Overrides:

getStreamerName in class Expression

Returns:

the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class