net.sf.saxon.expr
Class TailExpression

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.TailExpression

All Implemented Interfaces:

Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

public class TailExpression

extends ComputedExpression

A TailExpression represents a FilterExpression of the form EXPR[position() > n] Here n is usually 2, but we allow other values

See Also:

Serialized Form

Nested Class Summary

static class

TailExpression.TailIterator

Field Summary

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

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

TailExpression(Expression base, int start)
Construct a TailExpression, representing a filter expression of the form $base[position() >= $start]

Method Summary

int	computeCardinality()
int	computeSpecialProperties()
void	display(int level, NamePool pool, java.io.PrintStream out) Diagnostic print of expression structure.
boolean	equals(java.lang.Object other)
Expression	getBaseExpression()
ItemType	getItemType(TypeHierarchy th) Determine the data type of the expression, if possible.
int	getStart()
int	hashCode()
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
java.util.Iterator	iterateSubExpressions() Get the immediate sub-expressions of this expression.
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer) Offer promotion for this subexpression.
Expression	typeCheck(StaticContext env, ItemType contextItemType) Perform type checking of an expression and its subexpressions.

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, simplify, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

TailExpression

public TailExpression(Expression base,
                      int start)

Construct a TailExpression, representing a filter expression of the form $base[position() >= $start]

Parameters:

base - the expression to be filtered

start - the position (1-based) of the first item to be included

Method Detail

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Description copied from interface: Expression

Perform type checking of an expression and its subexpressions.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

Parameters:

env - the static context of the expression

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

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           ItemType contextItemType)
                    throws XPathException

Description copied from interface: Expression

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.

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

env - the static context of the expression

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

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Description copied from class: ComputedExpression

Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

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

computeSpecialProperties

public int computeSpecialProperties()

Overrides:

computeSpecialProperties in class ComputedExpression

getItemType

public ItemType getItemType(TypeHierarchy th)

Description copied from interface: Expression

Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

This method should always return a result, though it may be the best approximation that is available at the time.

Parameters:

th -

Returns:

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

computeCardinality

public int computeCardinality()

Specified by:

computeCardinality in class ComputedExpression

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()

Description copied from class: ComputedExpression

Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

an iterator containing the sub-expressions of this expression

getBaseExpression

public Expression getBaseExpression()

getStart

public int getStart()

equals

public boolean equals(java.lang.Object other)

hashCode

public int hashCode()

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Description copied from class: ComputedExpression

Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Specified by:

iterate in interface Expression

Overrides:

iterate in class ComputedExpression

Parameters:

context - supplies the context for evaluation

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

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)

Description copied from interface: Expression

Diagnostic print of expression structure. The expression is written to the System.err output stream

Parameters:

level - indentation level for this expression

pool - NamePool used to expand any names appearing in the expression

out - Output destination