net.sf.saxon.expr
Class CastableExpression

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.UnaryExpression
          net.sf.saxon.expr.CastableExpression

All Implemented Interfaces:

Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, InstructionInfoProvider

public final class CastableExpression
extends UnaryExpression

Castable Expression: implements "Expr castable as atomic-type?". The implementation simply wraps a cast expression with a try/catch.

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

CastableExpression(Expression source, AtomicType target, boolean allowEmpty)

Method Summary

boolean	allowsEmpty() Determine whether the empty sequence is allowed
int	computeCardinality() Determine the static cardinality.
int	computeSpecialProperties() Determine the special properties of this expression
boolean	effectiveBooleanValue(XPathContext context) Get the effective boolean value of the expression.
boolean	equals(Object other) Is this expression the same as another expression?
Item	evaluateItem(XPathContext context) Evaluate the expression
ItemType	getItemType(TypeHierarchy th) Determine the data type of the result of the Castable expression
AtomicType	getTargetType() Get the target type
static boolean	isCastable(AtomicValue value, AtomicType targetType, XPathContext context)
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Optimize the expression
Expression	simplify(StaticContext env) Simplify the expression
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression

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

display, getBaseExpression, hashCode, iterateSubExpressions, promote, replaceSubExpression

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, evaluateAsString, getCardinality, getColumnNumber, getContainingProcedure, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CastableExpression

public CastableExpression(Expression source,
                          AtomicType target,
                          boolean allowEmpty)

Method Detail

getTargetType

public AtomicType getTargetType()

Get the target type

allowsEmpty

public boolean allowsEmpty()

Determine whether the empty sequence is allowed

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify the expression

Overrides:

simplify in class UnaryExpression

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

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

Type-check the expression

Overrides:

typeCheck in class UnaryExpression

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:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

optimize

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

Optimize the expression

Overrides:

optimize in class UnaryExpression

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:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

equals

public boolean equals(Object other)

Is this expression the same as another expression?

Overrides:

equals in class UnaryExpression

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the result of the Castable expression

Overrides:

getItemType in class UnaryExpression

Parameters:

th -

Returns:

the item type of the items in the result sequence, insofar as this is known statically.

computeCardinality

public int computeCardinality()

Description copied from class: UnaryExpression

Determine the static cardinality. Default implementation returns the cardinality of the operand

Overrides:

computeCardinality in class UnaryExpression

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class UnaryExpression

Returns:

StaticProperty.NON_CREATIVE.

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the expression

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Expression

Parameters:

context - The context in which the expression is to be evaluated

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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException

Description copied from class: Expression

Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Overrides:

effectiveBooleanValue in class Expression

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the effective boolean value

Throws:

XPathException - if any dynamic error occurs evaluating the expression

isCastable

public static boolean isCastable(AtomicValue value,
                                 AtomicType targetType,
                                 XPathContext context)