net.sf.saxon.expr
Class CastExpression

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

All Implemented Interfaces:

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

public final class CastExpression
extends UnaryExpression

Cast Expression: implements "cast as data-type ( expression )". It also allows an internal cast, which has the same semantics as a user-requested cast, but maps an empty sequence to an empty sequence.

See Also:

Serialized Form

Field Summary

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

operand

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

CastExpression(Expression source, AtomicType target, boolean allowEmpty)
Create a cast expression

Method Summary

boolean	allowsEmpty() Ask whether the expression accepts an empty sequence as input (producing an empty sequence as output)
static AtomicValue	castStringToQName(CharSequence operand, AtomicType targetType, StaticContext env) Evaluate the "pseudo-cast" of a string literal to a QName or NOTATION value.
int	computeCardinality() Get the static cardinality of the expression
int	computeSpecialProperties() Determine the special properties of this expression
Expression	copy() Copy an expression.
boolean	equals(Object other) Is this expression the same as another expression?
Item	evaluateItem(XPathContext context) Evaluate the expression
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
ItemType	getItemType(TypeHierarchy th) Get the static type of the expression
AtomicType	getTargetPrimitiveType() Get the primitive base type of the target type of the cast
AtomicType	getTargetType() Get the target type (the result type)
int	hashCode() get HashCode for comparing two expressions.
static boolean	isPossibleCast(int source, int target) Determine whether casting from a source type to a target type is possible
boolean	isUpCast() Ask whether this is a cast to a supertype of the original type
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	simplify(ExpressionVisitor visitor) Simplify the expression
boolean	targetIsDerived() Ask whether the target type is a derived type (not a primitive type)
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression

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

displayOperator, getBaseExpression, iterateSubExpressions, promote, replaceSubExpression

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, 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, hasLoopingSubexpression, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

CastExpression

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

Create a cast expression

Parameters:

source - expression giving the value to be converted

target - the type to which the value is to be converted

allowEmpty - true if the expression allows an empty sequence as input, producing an empty sequence as output. If false, an empty sequence is a type error.

Method Detail

isPossibleCast

public static boolean isPossibleCast(int source,
                                     int target)

Determine whether casting from a source type to a target type is possible

Parameters:

source - a primitive type (one that has an entry in the casting table)

target - another primitive type

Returns:

true if the entry in the casting table is either "Y" (casting always succeeds) or "M" (casting allowed but may fail for some values)

getTargetPrimitiveType

public AtomicType getTargetPrimitiveType()

Get the primitive base type of the target type of the cast

Returns:

the primitive type of the target type

getTargetType

public AtomicType getTargetType()

Get the target type (the result type)

Returns:

the target type

allowsEmpty

public boolean allowsEmpty()

Ask whether the expression accepts an empty sequence as input (producing an empty sequence as output)

Returns:

true if an empty sequence is accepted

targetIsDerived

public boolean targetIsDerived()

Ask whether the target type is a derived type (not a primitive type)

Returns:

true if the target type is a derived type

isUpCast

public boolean isUpCast()

Ask whether this is a cast to a supertype of the original type

Returns:

true if this is an upcast. This means the value stays unchanged and only the type label changes

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Simplify the expression

Overrides:

simplify in class UnaryExpression

Parameters:

visitor - an expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

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

Type-check the expression

Overrides:

typeCheck in class UnaryExpression

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)

optimize

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

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.

Overrides:

optimize in class UnaryExpression

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 if appropriate to optimize execution

Throws:

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

computeCardinality

public int computeCardinality()

Get the static cardinality of the expression

Overrides:

computeCardinality in class UnaryExpression

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)

Get the static type of the expression

Overrides:

getItemType in class UnaryExpression

Parameters:

th - the type hierarchy cache

Returns:

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

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class UnaryExpression

Returns:

StaticProperty.NON_CREATIVE.

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 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

equals

public boolean equals(Object other)

Is this expression the same as another expression?

Overrides:

equals in class UnaryExpression

hashCode

public int hashCode()

get HashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.

Overrides:

hashCode in class UnaryExpression

toString

public String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:

toString in class UnaryExpression

Returns:

a representation of the expression as a string

explain

public void explain(ExpressionPresenter out)

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

Overrides:

explain in class UnaryExpression

Parameters:

out - the expression presenter used to display the structure

castStringToQName

public static AtomicValue castStringToQName(CharSequence operand,
                                            AtomicType targetType,
                                            StaticContext env)
                                     throws XPathException

Evaluate the "pseudo-cast" of a string literal to a QName or NOTATION value. This can only happen at compile time

Parameters:

operand - the value to be converted

targetType - the type to which it is to be converted

env - the static context

Returns:

the QName or NOTATION value that results from casting the string to a QName. This will either be a QNameValue or a derived AtomicValue derived from QName or NOTATION

Throws:

XPathException