net.sf.saxon.expr
Class UnaryExpression

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.UnaryExpression
All Implemented Interfaces:
Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider
Direct Known Subclasses:
AtomicSequenceConverter, Atomizer, CardinalityChecker, CastableExpression, CastExpression, DocumentSorter, FirstItemExpression, InstanceOfExpression, ItemChecker, LazyExpression, NegateExpression, NumericPromoter, SingletonAtomizer, TailCallLoop, UntypedAtomicConverter

public abstract class UnaryExpression
extends Expression

Unary Expression: an expression taking a single operand expression

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
UnaryExpression(Expression p0)
           
 
Method Summary
 int computeCardinality()
          Determine the static cardinality.
 int computeSpecialProperties()
          Get the static properties of this expression (other than its type).
 boolean equals(Object other)
          Is this expression the same as another expression?
 void explain(ExpressionPresenter out)
          Diagnostic print of expression structure.
 Expression getBaseExpression()
           
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the expression, if possible.
 int hashCode()
          get HashCode for comparing two expressions.
 Iterator iterateSubExpressions()
          Get the immediate subexpressions of this expression
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 Expression promote(PromotionOffer offer)
          Promote this expression if possible
 boolean replaceSubExpression(Expression original, Expression replacement)
          Replace one subexpression by a replacement subexpression
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression
 String toString()
          The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Type-check the expression.
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, copy, display, doPromotion, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

UnaryExpression

public UnaryExpression(Expression p0)
Method Detail

getBaseExpression

public Expression getBaseExpression()

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
Simplify an expression

Overrides:
simplify in class Expression
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. Default implementation for unary operators that accept any kind of operand

Overrides:
typeCheck in class Expression
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
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 Expression
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)

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException
Promote this expression if possible

Overrides:
promote in class Expression
Parameters:
offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
Returns:
if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
Throws:
XPathException - if any error is detected

iterateSubExpressions

public Iterator iterateSubExpressions()
Get the immediate subexpressions of this expression

Overrides:
iterateSubExpressions in class Expression
Returns:
an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression

Overrides:
replaceSubExpression in class Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

computeSpecialProperties

public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Returns:
the special properties, as a bit-significant integer

computeCardinality

public int computeCardinality()
Determine the static cardinality. Default implementation returns the cardinality of the operand

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

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible. The default implementation for unary expressions returns the item type of the operand

Specified by:
getItemType in class Expression
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 Object

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 Object

toString

public String toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:
toString in class Expression

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:
explain in class Expression
Parameters:
out - the expression presenter used to display the structure


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