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## 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, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, 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, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD`

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

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
`Expression` | `copy()` Copy an 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
`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
`int` | `hashCode()` get HashCode for comparing two expressions.
`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
`displayOperator, getBaseExpression, iterateSubExpressions, promote, replaceSubExpression, toString`

Methods inherited from class net.sf.saxon.expr.Expression
`addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, 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

### 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(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`

### 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

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Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.