com.saxonica.expr
Class TryCatch

java.lang.Object
  net.sf.saxon.expr.Expression
      com.saxonica.expr.TryCatch

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator

public class TryCatch
extends Expression

This class implements a try/catch expression. It consists of a try expression, and a sequence of Nametest/Catch expression pairs. If the try expression succeeds, its result is returned; otherwise the error code of the exception is matched against each of the Nametests in turn, and the first matching catch expression is evaluated.

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD

Constructor Summary

TryCatch(Expression tryExpr)

Method Summary

void	addCatchExpression(QNameTest test, Expression catchExpr)
int	computeCardinality() Determine the cardinality of the function.
Expression	copy() Copy an expression.
Item	evaluateItem(XPathContext c) Evaluate as a singleton item
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
ItemType	getItemType(TypeHierarchy th) Determine the item type of the value returned by the function
boolean	hasLoopingSubexpression(Expression child) Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
SequenceIterator	iterate(XPathContext c) Iterate over the results of the function
Iterator<Expression>	iterateSubExpressions() Get the immediate sub-expressions of this expression.
Expression	promote(PromotionOffer offer, Expression parent) Offer promotion for this subexpression.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Perform type checking of an expression and its subexpressions.

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getExpressionName, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, optimize, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

TryCatch

public TryCatch(Expression tryExpr)

Method Detail

addCatchExpression

public void addCatchExpression(QNameTest test,
                               Expression catchExpr)

computeCardinality

public int computeCardinality()

Determine the cardinality of the function.

Specified by:

computeCardinality in class Expression

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

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the item type of the value returned by the function

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

Returns:

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

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException

Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

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.

If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Overrides:

typeCheck in class Expression

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)

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Get the immediate sub-expressions of this expression.

Overrides:

iterateSubExpressions in class Expression

Returns:

an iterator containing the sub-expressions of this expression

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)

Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly

Overrides:

hasLoopingSubexpression in class Expression

Parameters:

child - the immediate subexpression

Returns:

true if the child expression is evaluated repeatedly

promote

public Expression promote(PromotionOffer offer,
                          Expression parent)
                   throws XPathException

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.

This method must be overridden for any Expression that has subexpressions.

Overrides:

promote in class Expression

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

parent -

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

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

copy

public Expression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

evaluateItem

public Item evaluateItem(XPathContext c)
                  throws XPathException

Evaluate as a singleton item

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Expression

Parameters:

c - the dynamic XPath evaluation context

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

iterate

public SequenceIterator iterate(XPathContext c)
                         throws XPathException

Iterate over the results of the function

Specified by:

iterate in interface SequenceIterable

Overrides:

iterate in class Expression

Parameters:

c - 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

explain

public void explain(ExpressionPresenter out)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

explain in class Expression

Parameters:

out - the expression presenter used to display the structure