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

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, org.xml.sax.Locator
```
public final class ItemChecker
extends UnaryExpression
```
A ItemChecker implements the item type checking of "treat as": that is, it returns the supplied sequence, checking that all its items are of the correct 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

ItemChecker(Expression sequence, ItemType itemType, RoleLocator role)
Constructor

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`Expression`	`copy()`	Copy an expression.
`boolean`	`equals(java.lang.Object other)`	Is this expression the same as another expression?
`Item`	`evaluateItem(XPathContext context)`	Evaluate as an Item.
`void`	`explain(ExpressionPresenter out)`	Diagnostic print of expression structure.
`int`	`getImplementationMethod()`	An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
`ItemType`	`getItemType(TypeHierarchy th)`	Determine the data type of the items returned by the expression
`ItemType`	`getRequiredType()`	Get the required type
`RoleLocator`	`getRoleLocator()`	Get the RoleLocator (used to construct error messages)
`SequenceIterator`	`iterate(XPathContext context)`	Iterate over the sequence of values
`void`	`process(XPathContext context)`	Process the instruction, without returning any tail calls
`Expression`	`simplify(ExpressionVisitor visitor)`	Simplify an expression
`Expression`	`typeCheck(ExpressionVisitor visitor, ItemType contextItemType)`	Type-check the expression

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

Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, markTailFunctionCalls, 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
  - ItemChecker
```
public ItemChecker(Expression sequence,
                   ItemType itemType,
                   RoleLocator role)
```
    Constructor
    
    Parameters:
    
    sequence - the expression whose value we are checking
    
    itemType - the required type of the items in the sequence
    
    role - information used in constructing an error message
- Method Detail
  - getRequiredType
```
public ItemType getRequiredType()
```
    Get the required type
    
    Returns:
    
    the required type of the items in the sequence
  - getRoleLocator
```
public RoleLocator getRoleLocator()
```
    Get the RoleLocator (used to construct error messages)
    
    Returns:
    
    the RoleLocator
  - simplify
```
public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
```
    Simplify an 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)
  - getImplementationMethod
```
public int getImplementationMethod()
```
    An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided. This implementation provides both iterate() and process() methods natively.
    
    Overrides:
    
    getImplementationMethod in class Expression
    
    Returns:
    
    the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD
  - iterate
```
public SequenceIterator iterate(XPathContext context)
                         throws XPathException
```
    Iterate over the sequence of values
    
    Specified by:
    
    iterate in interface SequenceIterable
    
    Overrides:
    
    iterate in class Expression
    
    Parameters:
    
    context - supplies the context for evaluation
    
    Returns:
    
    a SequenceIterator that can be used to iterate over the result of the expression
    
    Throws:
    
    XPathException - if any dynamic error occurs evaluating the expression
  - evaluateItem
```
public Item evaluateItem(XPathContext context)
                  throws XPathException
```
    Evaluate as an Item.
    
    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
  - process
```
public void process(XPathContext context)
             throws XPathException
```
    Process the instruction, without returning any tail calls
    
    Overrides:
    
    process in class Expression
    
    Parameters:
    
    context - The dynamic context, giving access to the current node, the current variables, etc.
    
    Throws:
    
    XPathException
  - 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 items returned by 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.
  - equals
```
public boolean equals(java.lang.Object other)
```
    Is this expression the same as another expression?
    
    Overrides:
    
    equals in class UnaryExpression
  - 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 ItemChecker

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

ItemChecker

Method Detail

getRequiredType

getRoleLocator

simplify

typeCheck

getImplementationMethod

iterate

evaluateItem

process

copy

getItemType

equals

explain