net.sf.saxon.expr
Class ExpressionVisitor

java.lang.Object
  net.sf.saxon.expr.ExpressionVisitor

public class ExpressionVisitor
extends Object

The ExpressionVisitor supports the various phases of processing of an expression tree which require a recursive walk of the tree structure visiting each node in turn. In maintains a stack holding the ancestor nodes of the node currently being visited.

Constructor Summary

ExpressionVisitor()
Create an ExpressionVisitor

Method Summary

Configuration	getConfiguration() Get the Saxon configuration
Expression	getCurrentExpression() Get the current expression, the one being visited
Executable	getExecutable() Get the Executable containing the expressions being visited
Expression	getParentExpression() Get the parent expression of the current expression in the expression tree
Stack<Expression>	getStack() Get the stack containing all the expressions currently being visited
StaticContext	getStaticContext() Get the static context for the expressions being visited.
boolean	isLoopingSubexpression(Expression ancestor) Return true if the current expression at the top of the visitor's stack is evaluated repeatedly when a given ancestor expression is evaluated once
static ExpressionVisitor	make(StaticContext env) Factory method: make an expression visitor
Expression	optimize(Expression exp, ItemType contextItemType) Optimize an expression, via the ExpressionVisitor
void	resetStaticProperties() Reset the static properties for the current expression and for all its containing expressions.
void	setConfiguration(Configuration configuration) Set the Saxon configuration
void	setExecutable(Executable executable) Set the Executable containing the expressions being visited
void	setStack(Stack<Expression> stack) Set the stack used to hold the expressions being visited
void	setStaticContext(StaticContext staticContext) Set the static context for the expressions being visited.
Expression	simplify(Expression exp) Simplify an expression, via the ExpressionVisitor
Expression	typeCheck(Expression exp, ItemType contextItemType) Type check an expression, via the ExpressionVisitor

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExpressionVisitor

public ExpressionVisitor()

Create an ExpressionVisitor

Method Detail

getConfiguration

public Configuration getConfiguration()

Get the Saxon configuration

Returns:

the Saxon configuration

setConfiguration

public void setConfiguration(Configuration configuration)

Set the Saxon configuration

Parameters:

configuration - the Saxon configuration

getExecutable

public Executable getExecutable()

Get the Executable containing the expressions being visited

Returns:

the Executable

setExecutable

public void setExecutable(Executable executable)

Set the Executable containing the expressions being visited

Parameters:

executable - the Executable

getStack

public Stack<Expression> getStack()

Get the stack containing all the expressions currently being visited

Returns:

the expression stack holding all the containing expressions of the current expression; the objects on this Stack are instances of Expression

setStack

public void setStack(Stack<Expression> stack)

Set the stack used to hold the expressions being visited

Parameters:

stack - the expression stack

getStaticContext

public StaticContext getStaticContext()

Get the static context for the expressions being visited. Note: this may not reflect all changes in static context (e.g. namespace context, base URI) applying to nested expressions

Returns:

the static context

setStaticContext

public void setStaticContext(StaticContext staticContext)

Set the static context for the expressions being visited. Note: this may not reflect all changes in static context (e.g. namespace context, base URI) applying to nested expressions

Parameters:

staticContext - the static context

getCurrentExpression

public Expression getCurrentExpression()

Get the current expression, the one being visited

Returns:

the current expression

make

public static ExpressionVisitor make(StaticContext env)

Factory method: make an expression visitor

Parameters:

env - the static context

Returns:

the new expression visitor

simplify

public Expression simplify(Expression exp)
                    throws XPathException

Simplify an expression, via the ExpressionVisitor

Parameters:

exp - the expression to be simplified

Returns:

the simplified expression

Throws:

XPathException

typeCheck

public Expression typeCheck(Expression exp,
                            ItemType contextItemType)
                     throws XPathException

Type check an expression, via the ExpressionVisitor

Parameters:

exp - the expression to be typechecked

contextItemType - the static type of the context item for this expression

Returns:

the expression that results from type checking (this may be wrapped in expressions that perform dynamic checking of the item type or cardinality, or that perform atomization or numeric promotion)

Throws:

XPathException - if static type checking fails, that is, if the expression cannot possibly deliver a value of the required type

optimize

public Expression optimize(Expression exp,
                           ItemType contextItemType)
                    throws XPathException

Optimize an expression, via the ExpressionVisitor

Parameters:

exp - the expression to be typechecked

contextItemType - the static type of the context item for this expression

Returns:

the rewritten expression

Throws:

XPathException

getParentExpression

public Expression getParentExpression()

Get the parent expression of the current expression in the expression tree

Returns:

the parent of the current expression (or null if this is the root)

isLoopingSubexpression

public boolean isLoopingSubexpression(Expression ancestor)

Return true if the current expression at the top of the visitor's stack is evaluated repeatedly when a given ancestor expression is evaluated once

Parameters:

ancestor - the ancestor expression. May be null, in which case the search goes all the way to the base of the stack.

Returns:

true if the current expression is evaluated repeatedly

resetStaticProperties

public final void resetStaticProperties()

Reset the static properties for the current expression and for all its containing expressions. This should be done whenever the expression is changed in a way that might affect the properties. It causes the properties to be recomputed next time they are needed.