## 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)

Copyright (C) Michael H. Kay. All rights reserved.