net.sf.saxon.expr
Class PathExpression

java.lang.Object
  extended bynet.sf.saxon.expr.ComputedExpression
      extended bynet.sf.saxon.expr.PathExpression
All Implemented Interfaces:
Expression, MappingFunction, Serializable

public final class PathExpression
extends ComputedExpression
implements MappingFunction

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.

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
lineNumber, NO_ARGUMENTS, staticProperties
 
Constructor Summary
PathExpression(Expression start, Expression step)
          Constructor
 
Method Summary
 Expression analyze(StaticContext env)
          Type-check the expression
 int computeCardinality()
          Determine the static cardinality of the expression
 int computeDependencies()
          Determine which aspects of the context the expression depends on.
 int computeSpecialProperties()
          Get the static properties of this expression (other than its type).
 void display(int level, NamePool pool)
          Diagnostic print of expression structure
 boolean equals(Object other)
          Is this expression the same as another expression?
 Expression getAllExceptLastStep()
          Get all steps before the last.
 Expression getFirstStep()
          Get the first step in this expression.
 ItemType getItemType()
          Determine the data type of the items returned by this exprssion
 Expression getLastStep()
          Get the last step in this expression.
 Expression getRemainingSteps()
          Get all steps after the first.
 Expression[] getSubExpressions()
          Get the immediate subexpressions of this expression
 int hashCode()
          get HashCode for comparing two expressions
 SequenceIterator iterate(XPathContext context)
          Iterate the path-expression in a given context
 Object map(Item item, XPathContext context, Object info)
          Mapping function, from a node returned by the start iteration, to a sequence returned by the child.
 Expression promote(PromotionOffer offer)
          Promote this expression if possible
 Expression simplify()
          Simplify an expression
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getDependencies, getIntrinsicDependencies, getLineNumber, getSpecialProperties, markTailFunctionCalls, setLineNumber, typeError
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 

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

getItemType

public final ItemType getItemType()
Determine the data type of the items returned by this exprssion

Specified by:
getItemType in interface Expression
Returns:
Type.NODE, or some subtype thereof

simplify

public Expression simplify()
                    throws XPathException
Simplify an expression

Specified by:
simplify in interface Expression
Overrides:
simplify in class ComputedExpression
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

analyze

public Expression analyze(StaticContext env)
                   throws XPathException
Type-check the expression

Specified by:
analyze in interface Expression
Parameters:
env - the static context of the expression
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)

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException
Promote this expression if possible

Specified by:
promote in interface Expression
Overrides:
promote in class ComputedExpression
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

getSubExpressions

public Expression[] getSubExpressions()
Get the immediate subexpressions of this expression

Specified by:
getSubExpressions in interface Expression
Overrides:
getSubExpressions in class ComputedExpression
Returns:
an array containing the sub-expressions of this expression

computeDependencies

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

Overrides:
computeDependencies in class ComputedExpression
Returns:
the depencies, as a bit-mask

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 ComputedExpression

computeCardinality

public int computeCardinality()
Determine the static cardinality of the expression

Specified by:
computeCardinality in class ComputedExpression

equals

public boolean equals(Object other)
Is this expression the same as another expression?


hashCode

public int hashCode()
get HashCode for comparing two expressions


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


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


getLastStep

public Expression getLastStep()
Get the last step in this expression. A path expression A/B/C is represented as (A/B)/C, but the last step is C


getAllExceptLastStep

public Expression getAllExceptLastStep()
Get all steps before the last.


iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Iterate the path-expression in a given context

Specified by:
iterate in interface Expression
Overrides:
iterate in class ComputedExpression
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

map

public Object map(Item item,
                  XPathContext context,
                  Object info)
           throws XPathException
Mapping function, from a node returned by the start iteration, to a sequence returned by the child.

Specified by:
map in interface MappingFunction
Parameters:
item - The item to be mapped. If context is supplied, this must be the same as context.currentItem().
context - The processing context. This is supplied only for mapping constructs that set the context node, position, and size. Otherwise it is null.
info - Arbitrary information supplied by the creator of the MappingIterator. It must be read-only and immutable for the duration of the iteration.
Returns:
either (a) a SequenceIterator over the sequence of items that the supplied input item maps to, or (b) an Item if it maps to a single item, or (c) null if it maps to an empty sequence.
Throws:
XPathException

display

public void display(int level,
                    NamePool pool)
Diagnostic print of expression structure

Specified by:
display in interface Expression
Parameters:
level - indentation level for this expression