net.sf.saxon.expr
Class ItemChecker

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.UnaryExpression
          extended by net.sf.saxon.expr.ItemChecker
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, 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
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD
 
Constructor Summary
ItemChecker(Expression sequence, ItemType itemType, RoleLocator role)
          Constructor
 
Method Summary
 Expression copy()
          Copy an expression.
 boolean equals(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.
 String getExpressionName()
          Get a name identifying the kind of expression, in terms meaningful to a user.
 int getImplementationMethod()
          An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
 IntegerValue[] getIntegerBounds()
          For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the items returned by the expression
 ItemMappingFunction getMappingFunction(XPathContext context)
          Get the mapping function used to implement this item check.
 ItemType getRequiredType()
          Get the required type
 RoleLocator getRoleLocator()
          Get the RoleLocator (used to construct error messages)
 int hashCode()
          get HashCode for comparing two expressions.
 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, ExpressionVisitor.ContextItemType contextItemType)
          Type-check the expression
 
Methods inherited from class net.sf.saxon.expr.UnaryExpression
computeCardinality, computeSpecialProperties, displayOperator, getBaseExpression, iterateSubExpressions, optimize, promote, replaceSubExpression, toString
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, 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

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,
                            ExpressionVisitor.ContextItemType 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

getIntegerBounds

public IntegerValue[] getIntegerBounds()
For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.

Overrides:
getIntegerBounds in class Expression
Returns:
the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Iterate over the sequence of values

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

getMappingFunction

public ItemMappingFunction getMappingFunction(XPathContext context)
Get the mapping function used to implement this item check. This mapping function is applied to each item in the input sequence.

Parameters:
context - The dynamic context used to evaluate the mapping function
Returns:
the mapping function. This will be an identity mapping: the output sequence is the same as the input sequence, unless the dynamic type checking reveals an error.

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Evaluate as an Item.

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 - if a dynamic error occurs

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(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

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

getExpressionName

public String getExpressionName()
Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:
getExpressionName in class Expression
Returns:
a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.


Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.