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

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, org.xml.sax.Locator
```
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.UnaryExpression
  operand
- Fields inherited from class net.sf.saxon.expr.Expression
  EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties

Constructor Summary

Constructors
Constructor	Description
`CastableExpression(Expression source, AtomicType target, boolean allowEmpty)`	Create a "castable" expression of the form "source castable as target"

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`boolean`	`allowsEmpty()`	Determine whether the empty sequence is allowed
`int`	`computeCardinality()`	Determine the static cardinality.
`int`	`computeSpecialProperties()`	Determine the special properties of this expression
`Expression`	`copy()`	Copy an expression.
`boolean`	`effectiveBooleanValue(XPathContext context)`	Get the effective boolean value of the expression.
`boolean`	`equals(java.lang.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)`	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)`	Determine whether a value is castable to a given type
`Expression`	`optimize(ExpressionVisitor visitor, ItemType contextItemType)`	Optimize the expression
`Expression`	`simplify(ExpressionVisitor visitor)`	Simplify the expression
`Expression`	`typeCheck(ExpressionVisitor visitor, ItemType contextItemType)`	Type-check the expression

Methods inherited from class net.sf.saxon.expr.UnaryExpression
displayExpressionName, displayOperator, getBaseExpression, hashCode, iterateSubExpressions, promote, replaceSubExpression, toString

Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, dynamicError, evaluateAsString, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterate, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - CastableExpression
```
public CastableExpression(Expression source,
                          AtomicType target,
                          boolean allowEmpty)
```
    Create a "castable" expression of the form "source castable as target"
    
    Parameters:
    
    source - The source expression
    
    target - The type being tested against
    
    allowEmpty - true if an empty sequence is acceptable, that is if the expression was written as "source castable as target?"
- Method Detail
  - getTargetType
```
public AtomicType getTargetType()
```
    Get the target type
    
    Returns:
    
    the target type
  - allowsEmpty
```
public boolean allowsEmpty()
```
    Determine whether the empty sequence is allowed
    
    Returns:
    
    true if an empty sequence is allowed
  - 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
```
    Optimize the expression
    
    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)
  - equals
```
public boolean equals(java.lang.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 - the type hierarchy cache
    
    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
    
    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
  - 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
  - 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)
```
    Determine whether a value is castable to a given type
    
    Parameters:
    
    value - the value to be tested
    
    targetType - the type to be tested against
    
    context - XPath dynamic context
    
    Returns:
    
    true if the value is castable to the required type
  - 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

Class CastableExpression

Field Summary

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

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

Constructor Summary

Method Summary

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

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

Methods inherited from class java.lang.Object

Constructor Detail

CastableExpression

Method Detail

getTargetType

allowsEmpty

simplify

typeCheck

optimize

equals

getItemType

computeCardinality

computeSpecialProperties

copy

evaluateItem

effectiveBooleanValue

isCastable

explain