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

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, org.xml.sax.Locator
```
public final class InstanceOfExpression
extends UnaryExpression
```
InstanceOf Expression: implements "Expr instance of data-type"

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
`InstanceOfExpression(Expression source, SequenceType target)`	Construct an "instance of" expression in the form "source instance of target"

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`int`	`computeCardinality()`	Determine the cardinality
`Expression`	`copy()`	Copy an expression.
`boolean`	`effectiveBooleanValue(XPathContext context)`	Evaluate the expression as a boolean
`boolean`	`equals(java.lang.Object other)`	Is this expression the same as another expression?
`Item`	`evaluateItem(XPathContext context)`	Evaluate the expression
`void`	`explain(ExpressionPresenter destination)`	Diagnostic print of expression structure.
`ItemType`	`getItemType(TypeHierarchy th)`	Determine the data type of the result of the InstanceOf expression
`int`	`getRequiredCardinality()`	Get the cardinality that we are testing for membership of
`ItemType`	`getRequiredItemType()`	Get the item type that we are testing for membership of
`Expression`	`optimize(ExpressionVisitor visitor, ItemType contextItemType)`	Perform optimisation of an expression and its subexpressions.
`Expression`	`typeCheck(ExpressionVisitor visitor, ItemType contextItemType)`	Type-check the expression

Methods inherited from class net.sf.saxon.expr.UnaryExpression
computeSpecialProperties, displayExpressionName, displayOperator, getBaseExpression, hashCode, iterateSubExpressions, promote, replaceSubExpression, simplify, 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
  - InstanceOfExpression
```
public InstanceOfExpression(Expression source,
                            SequenceType target)
```
    Construct an "instance of" expression in the form "source instance of target"
    
    Parameters:
    
    source - the expression whose type is to be tested
    
    target - the type against which it is tested
- Method Detail
  - getRequiredItemType
```
public ItemType getRequiredItemType()
```
    Get the item type that we are testing for membership of
    
    Returns:
    
    the item type
  - getRequiredCardinality
```
public int getRequiredCardinality()
```
    Get the cardinality that we are testing for membership of
    
    Returns:
    
    the required cardinality
  - 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 checked expression
    
    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)
  - equals
```
public boolean equals(java.lang.Object other)
```
    Is this expression the same as another expression?
    
    Overrides:
    
    equals in class UnaryExpression
  - computeCardinality
```
public int computeCardinality()
```
    Determine the cardinality
    
    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
  - 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
  - getItemType
```
public ItemType getItemType(TypeHierarchy th)
```
    Determine the data type of the result of the InstanceOf 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.
  - 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
```
    Evaluate the expression as a boolean
    
    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
  - explain
```
public void explain(ExpressionPresenter destination)
```
    Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
    
    Overrides:
    
    explain in class UnaryExpression
    
    Parameters:
    
    destination - the expression presenter used to display the structure

Class InstanceOfExpression

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

InstanceOfExpression

Method Detail

getRequiredItemType

getRequiredCardinality

typeCheck

optimize

equals

computeCardinality

copy

getItemType

evaluateItem

effectiveBooleanValue

explain