Package net.sf.saxon.expr
Class AxisExpression
java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.AxisExpression
- All Implemented Interfaces:
ExportAgent
,Locatable
,IdentityComparable
,Traceable
An AxisExpression is always obtained by simplifying a PathExpression.
It represents a PathExpression that starts at the context node, and uses
a simple node-test with no filters. For example "*", "title", "./item",
"@*", or "ancestor::chapter*".
An AxisExpression delivers nodes in axis order (not in document order). To get nodes in document order, in the case of a reverse axis, the expression should be wrapped in a call on reverse().
-
Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
Elaborator for an AxisExpression -
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
ConstructorsConstructorDescriptionAxisExpression
(int axis, NodeTest nodeTest) Constructor for an AxisExpression whose origin is the context item -
Method Summary
Modifier and TypeMethodDescriptionaddToPathMap
(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.protected final int
Determine the cardinality of the result of this expressionprotected int
get HashCode for comparing two expressionsprotected int
Get the static properties of this expression (other than its type).copy
(RebindingMap rebindings) Copy an expression.boolean
Is this expression the same as another expression?void
export
(ExpressionPresenter destination) Diagnostic print of expression structure.int
getAxis()
Get the axisGet the static type of the context item for this AxisExpression.double
getCost()
Return the estimated cost of evaluating an expression.Make an elaborator for this expressionGet a name identifying the kind of expression, in terms meaningful to a user.int
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().int
Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.final ItemType
Determine the data type of the items returned by this expressionGet the NodeTest.Find any necessary preconditions for the satisfaction of this expression as a set of boolean expressions to be evaluated on the context nodegetStaticUType
(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.Get the (partial) name of a class that supports streaming of this kind of expressionboolean
Ask whether there is a possibility that the context item will be undefinedboolean
Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.iterate
(XPathContext context) Evaluate the path-expression in a given context to return a NodeSetIterate the axis from a given starting node, without regard to contextoptimize
(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform optimisation of an expression and its subexpressions.void
setAxis
(int axis) Set the axissimplify()
Simplify an expressiontoPattern
(Configuration config) Convert this expression to an equivalent XSLT patternProduce a short string identifying the expression for use in error messagestoString()
Represent the expression as a string.typeCheck
(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Type-check the expressionMethods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dispatchTailCall, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, getCardinality, getConfiguration, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isUpdatingExpression, isVacuousExpression, makeElaborator, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplifyChildren, staticTypeCheck, supportsLazyEvaluation, suppressValidation, typeCheckChildren, typeError, unordered, verifyParentPointers, withLocation
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface net.sf.saxon.trace.Traceable
gatherProperties
-
Constructor Details
-
AxisExpression
Constructor for an AxisExpression whose origin is the context item- Parameters:
axis
- The axis to be used in this AxisExpression: relevant constants are defined in classAxisInfo
.nodeTest
- The conditions to be satisfied by selected nodes. May be null, indicating that any node on the axis is acceptable- See Also:
-
-
Method Details
-
setAxis
public void setAxis(int axis) Set the axis- Parameters:
axis
- the new axis
-
getExpressionName
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.
-
simplify
Simplify an expression- Overrides:
simplify
in classExpression
- Returns:
- the simplified expression (or the original if unchanged, or if modified in-situ)
- Throws:
XPathException
- if an error is discovered during expression rewriting
-
typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException Type-check the expression- Overrides:
typeCheck
in classExpression
- Parameters:
visitor
- an expression visitorcontextInfo
- 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)
-
getContextItemType
Get the static type of the context item for this AxisExpression. May be null if not known.- Returns:
- the statically-inferred type, or null if not known
-
optimize
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 classExpression
- Parameters:
visitor
- an expression visitorcontextInfo
- 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 toType.ITEM_TYPE
- Returns:
- the original expression, rewritten if appropriate to optimize execution
-
getCost
public double getCost()Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.- Overrides:
getCost
in classExpression
- Returns:
- the estimated cost
-
equals
Is this expression the same as another expression?- Overrides:
equals
in classExpression
- 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.
-
computeHashCode
protected int computeHashCode()get HashCode for comparing two expressions- Overrides:
computeHashCode
in classExpression
- Returns:
- a computed hash code
-
copy
Copy an expression. This makes a deep copy.- Specified by:
copy
in classExpression
- Parameters:
rebindings
- a mutable list of (old binding, new binding) pairs that is used to update the bindings held in any local variable references that are copied.- Returns:
- the copy of the original expression
-
computeSpecialProperties
protected int computeSpecialProperties()Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.- Overrides:
computeSpecialProperties
in classExpression
- Returns:
- the special properties, as a bit-significant integer
-
getItemType
Determine the data type of the items returned by this expression- Specified by:
getItemType
in classExpression
- Returns:
- Type.NODE or a subtype, based on the NodeTest in the axis step, plus information about the content type if this is known from schema analysis
-
getStaticUType
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 classExpression
- Parameters:
contextItemType
- the static type of the context item for the expression evaluation- Returns:
- the static item type of the expression according to the XSLT 3.0 defined rules
-
getIntrinsicDependencies
public int getIntrinsicDependencies()Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".- Overrides:
getIntrinsicDependencies
in classExpression
- Returns:
- a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
-
computeCardinality
protected final int computeCardinality()Determine the cardinality of the result of this expression- Specified by:
computeCardinality
in classExpression
- 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 returnStaticProperty.ALLOWS_ZERO
if the result is known to be an empty sequence, orStaticProperty.ALLOWS_MANY
if if is known to return a sequence of length two or more.
-
isSubtreeExpression
public boolean isSubtreeExpression()Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.- Overrides:
isSubtreeExpression
in classExpression
- Returns:
- true if the expression has no dependencies on the context node, or if the only dependencies on the context node are downward selections using the self, child, descendant, attribute, and namespace axes.
-
getAxis
public int getAxis()Get the axis- Returns:
- the axis number, for example
AxisInfo.CHILD
-
getNodeTest
Get the NodeTest. Returns null if the AxisExpression can return any node.- Returns:
- the node test, or null if all nodes are returned
-
addToPathMap
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 classExpression
- Parameters:
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
- the PathMapNodeSet to which the paths embodied in this expression should be added- 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
-
isContextPossiblyUndefined
public boolean isContextPossiblyUndefined()Ask whether there is a possibility that the context item will be undefined- Returns:
- true if this is a possibility
-
getContextItemStaticInfo
-
toPattern
Convert this expression to an equivalent XSLT pattern- Overrides:
toPattern
in classExpression
- Parameters:
config
- the Saxon configuration- Returns:
- the equivalent pattern
- Throws:
XPathException
- if conversion is not possible
-
getImplementationMethod
public int getImplementationMethod()Description copied from class:Expression
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 classExpression
- Returns:
- the implementation method, for example
Expression.ITERATE_METHOD
orExpression.EVALUATE_METHOD
orExpression.PROCESS_METHOD
-
iterate
Evaluate the path-expression in a given context to return a NodeSet- Overrides:
iterate
in classExpression
- 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
-
iterate
Iterate the axis from a given starting node, without regard to context- Parameters:
origin
- the starting node- Returns:
- the iterator over the axis
-
export
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
export
in interfaceExportAgent
- Specified by:
export
in classExpression
- 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.
-
toString
Represent the expression as a string. The resulting string will be a valid XPath 3.0 expression with no dependencies on namespace bindings other than the binding of the prefix "xs" to the XML Schema namespace.- Overrides:
toString
in classExpression
- Returns:
- the expression as a string in XPath 3.0 syntax
-
toShortString
Description copied from class:Expression
Produce a short string identifying the expression for use in error messages- Overrides:
toShortString
in classExpression
- Returns:
- a short string, sufficient to identify the expression
-
getStreamerName
Description copied from class:Expression
Get the (partial) name of a class that supports streaming of this kind of expression- Overrides:
getStreamerName
in classExpression
- 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
-
getPreconditions
Find any necessary preconditions for the satisfaction of this expression as a set of boolean expressions to be evaluated on the context node- Returns:
- A set of conditions, or null if none have been computed
-
getElaborator
Make an elaborator for this expression- Overrides:
getElaborator
in classExpression
- Returns:
- a suitable elaborator
-