PathExpression

java.lang.Object
- net.sf.saxon.expr.Expression
- - net.sf.saxon.expr.SlashExpression
  - - net.sf.saxon.expr.PathExpression

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction, EvaluableItem, SequenceIterable, InstructionInfo, org.xml.sax.Locator
```
public final class PathExpression
extends SlashExpression
implements ContextMappingFunction
```
An expression that establishes a set of nodes by following relationships between nodes in the document. Specifically, it consists of a start expression which defines a set of nodes, and a step which defines a relationship to be followed from those nodes to create a new set of nodes.
This class inherits from SlashExpression; it is used in the common case where the SlashExpression is known to return nodes rather than atomic values.

This class is not responsible for sorting the results into document order or removing duplicates. That is done by a DocumentSorter expression which is wrapped around the path expression. However, this class does contain the logic for deciding statically whether the DocumentSorter is needed or not.

See Also:

Serialized Form

Field Summary
- Fields inherited from class net.sf.saxon.expr.Expression
  EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties

Constructor Summary

Constructors
Constructor Description

PathExpression(Expression start, Expression step)
Constructor

Constructors
Constructor	Description
`PathExpression(Expression start, Expression step)`	Constructor

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`PathMap.PathMapNodeSet`	`addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)`	Add a representation of this expression to a PathMap.
`int`	`computeSpecialProperties()`	Get the static properties of this expression (other than its type).
`Expression`	`copy()`	Copy an expression.
`void`	`explain(ExpressionPresenter destination)`	Diagnostic print of expression structure.
`Expression`	`getFirstStep()`	Get the first step in this expression.
`Expression`	`getLastStep()`	Get the last step of the path expression
`Expression`	`getLeadingSteps()`	Get a path expression consisting of all steps except the last
`Expression`	`getRemainingSteps()`	Get all steps after the first.
`boolean`	`isAbsolute(TypeHierarchy th)`	Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
`boolean`	`isHybrid()`	Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values.
`SequenceIterator`	`iterate(XPathContext context)`	Iterate the path-expression in a given context
`Expression`	`optimize(ExpressionVisitor visitor, ItemType contextItemType)`	Optimize the expression and perform type analysis
`Expression`	`promote(PromotionOffer offer)`	Promote this expression if possible
`Expression`	`simplify(ExpressionVisitor visitor)`	Simplify an expression
`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.
`PathExpression`	`tryToMakeAbsolute(TypeHierarchy th)`	Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path.
`Expression`	`typeCheck(ExpressionVisitor visitor, ItemType contextItemType)`	Perform type analysis

Methods inherited from interface net.sf.saxon.expr.ContextMappingFunction
map

Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from class net.sf.saxon.expr.SlashExpression
computeCardinality, computeDependencies, equals, getItemType, getStartExpression, getStepExpression, hashCode, hasLoopingSubexpression, iterateSubExpressions, makeSlashExpression, map, promoteFocusIndependentSubexpressions, replaceSubExpression, setStartExpression, setStepExpression

- Constructor Detail
  - PathExpression
```
public PathExpression(Expression start,
                      Expression step)
```
    Constructor
    
    Parameters:
    
    start - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.
    
    step - The step to be followed from each node in the start expression to yield a new node-set
- Method Detail
  - isHybrid
```
public boolean isHybrid()
```
    Description copied from class: SlashExpression
    
    Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values. If so, this needs to be prevented at run time
    
    Overrides:
    
    isHybrid in class SlashExpression
    
    Returns:
    
    true if the static type allows both nodes and atomic values
  - simplify
```
public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
```
    Simplify an expression
    
    Overrides:
    
    simplify in class SlashExpression
    
    Parameters:
    
    visitor - the expression visitor
    
    Returns:
    
    the simplified expression
    
    Throws:
    
    XPathException - if an error is discovered during expression rewriting
  - typeCheck
```
public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException
```
    Perform type analysis
    
    Overrides:
    
    typeCheck in class SlashExpression
    
    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 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,
                           ItemType contextItemType)
                    throws XPathException
```
    Optimize the expression and perform type analysis
    
    Overrides:
    
    optimize in class SlashExpression
    
    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)
  - promote
```
public Expression promote(PromotionOffer offer)
                   throws XPathException
```
    Promote this expression if possible
    
    Overrides:
    
    promote in class SlashExpression
    
    Parameters:
    
    offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
    
    Returns:
    
    if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
    
    Throws:
    
    XPathException - if any error is detected
  - copy
```
public Expression copy()
```
    Copy an expression. This makes a deep copy.
    
    Overrides:
    
    copy in class SlashExpression
    
    Returns:
    
    the copy of the original expression
  - computeSpecialProperties
```
public 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 class SlashExpression
    
    Returns:
    
    the special properties, as a bit-significant integer
  - getFirstStep
```
public Expression getFirstStep()
```
    Get the first step in this expression. A path expression A/B/C is represented as (A/B)/C, but the first step is A
    
    Returns:
    
    the first step in the expression, after expanding any nested path expressions
  - getRemainingSteps
```
public Expression getRemainingSteps()
```
    Get all steps after the first. This is complicated by the fact that A/B/C is represented as ((A/B)/C; we are required to return B/C
    
    Returns:
    
    a path expression containing all steps in this path expression other than the first, after expanding any nested path expressions
  - getLastStep
```
public Expression getLastStep()
```
    Get the last step of the path expression
    
    Returns:
    
    the last step in the expression, after expanding any nested path expressions
  - getLeadingSteps
```
public Expression getLeadingSteps()
```
    Get a path expression consisting of all steps except the last
    
    Returns:
    
    a path expression containing all steps in this path expression other than the last, after expanding any nested path expressions
  - isAbsolute
```
public boolean isAbsolute(TypeHierarchy th)
```
    Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
    
    Parameters:
    
    th - the type hierarchy cache
    
    Returns:
    
    true if the first step in this path expression selects a document node
  - tryToMakeAbsolute
```
public PathExpression tryToMakeAbsolute(TypeHierarchy th)
```
    Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path. This is possible in cases where the path expression has the form a/b/c and it is known that the context item is a document node; in this case it is safe to change the path expression to /a/b/c
    
    Parameters:
    
    th - the type hierarchy cache
    
    Returns:
    
    the path expression if it is absolute; the converted path expression if it can be made absolute; or null if neither condition applies.
  - 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
  - iterate
```
public SequenceIterator iterate(XPathContext context)
                         throws XPathException
```
    Iterate the path-expression in a given context
    
    Specified by:
    
    iterate in interface SequenceIterable
    
    Overrides:
    
    iterate in class SlashExpression
    
    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
  - 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
  - explain
```
public void explain(ExpressionPresenter destination)
```
    Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
    
    Overrides:
    
    explain in class SlashExpression
    
    Parameters:
    
    destination - the expression presenter used to display the structure

Class PathExpression

Field Summary

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

Constructor Summary

Method Summary

Methods inherited from interface net.sf.saxon.expr.ContextMappingFunction

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

Methods inherited from class java.lang.Object

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

Constructor Detail

PathExpression

Method Detail

isHybrid

simplify

typeCheck

optimize

promote

copy

computeSpecialProperties

getFirstStep

getRemainingSteps

getLastStep

getLeadingSteps

isAbsolute

tryToMakeAbsolute

addToPathMap

iterate

toString

explain