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Java Source Code / Java Documentation » XML » XPath Saxon » net.sf.saxon.expr 
Source Cross Reference  Class Diagram Java Document (Java Doc) 


net.sf.saxon.expr.Expression

All known Subclasses:   net.sf.saxon.pattern.PatternSponsor,  net.sf.saxon.value.Value,  net.sf.saxon.expr.ComputedExpression,
Expression
public interface Expression extends Serializable(Code)
Interface supported by an XPath expression. This includes both compile-time and run-time methods.


Field Summary
final public static  intEVALUATE_METHOD
    
final public static  intITERATE_METHOD
    
final public static  intPROCESS_METHOD
    


Method Summary
public  voidcheckPermittedContents(SchemaType parentType, StaticContext env, boolean whole)
     Check statically that the results of the expression are capable of constructing the content of a given schema type.
public  voiddisplay(int level, NamePool pool, PrintStream out)
     Diagnostic print of expression structure.
 booleaneffectiveBooleanValue(XPathContext context)
     Get the effective boolean value of the expression.
public  StringevaluateAsString(XPathContext context)
     Evaluate an expression as a String.
 ItemevaluateItem(XPathContext context)
     Evaluate an expression as a single item.
 intgetCardinality()
    

Determine the static cardinality of the expression.

 intgetDependencies()
     Determine which aspects of the context the expression depends on.
public  intgetImplementationMethod()
     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 directly.
 ItemTypegetItemType(TypeHierarchy th)
     Determine the data type of the expression, if possible.
 ContainergetParentExpression()
     Get the container that immediately contains this expression.
 intgetSpecialProperties()
     Get the static properties of this expression (other than its type).
 SequenceIteratoriterate(XPathContext context)
     Return an Iterator to iterate over the values of a sequence.
 IteratoriterateSubExpressions()
     Get the immediate sub-expressions of this expression.
 Expressionoptimize(Optimizer opt, StaticContext env, ItemType contextItemType)
     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.


Parameters:
  opt - the optimizer in use.
public  voidprocess(XPathContext context)
    
 Expressionpromote(PromotionOffer offer)
     Offer promotion for this subexpression.
 Expressionsimplify(StaticContext env)
     Simplify an expression.
 ExpressiontypeCheck(StaticContext env, ItemType contextItemType)
     Perform type checking of an expression and its subexpressions.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion.


Field Detail
EVALUATE_METHOD
final public static int EVALUATE_METHOD(Code)



ITERATE_METHOD
final public static int ITERATE_METHOD(Code)



PROCESS_METHOD
final public static int PROCESS_METHOD(Code)





Method Detail
checkPermittedContents
public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException(Code)
Check statically that the results of the expression are capable of constructing the content of a given schema type.
Parameters:
  parentType - The schema type
Parameters:
  env - the static context
Parameters:
  whole - true if this expression is expected to make the whole content of the type, falseif it is expected to make up only a part
throws:
  XPathException - if the expression doesn't match the required content type



display
public void display(int level, NamePool pool, PrintStream out)(Code)
Diagnostic print of expression structure. The expression is written to the System.err output stream
Parameters:
  level - indentation level for this expression
Parameters:
  pool - NamePool used to expand any names appearing in the expression
Parameters:
  out - Output destination



effectiveBooleanValue
boolean effectiveBooleanValue(XPathContext context) throws XPathException(Code)
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.
Parameters:
  context - The context in which the expression is to be evaluated
exception:
  net.sf.saxon.trans.XPathException - if any dynamic error occurs evaluating theexpression the effective boolean value



evaluateAsString
public String evaluateAsString(XPathContext context) throws XPathException(Code)
Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.
exception:
  XPathException - if any dynamic error occurs evaluating theexpression
exception:
  ClassCastException - if the result type of theexpression is not xs:string?
Parameters:
  context - The context in which the expression is to be evaluated the value of the expression, evaluated in the current context.The expression must return a string or (); if the value of theexpression is (), this method returns "".



evaluateItem
Item evaluateItem(XPathContext context) throws XPathException(Code)
Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
Parameters:
  context - The context in which the expression is to be evaluated
exception:
  XPathException - if any dynamic error occurs evaluating theexpression the node or atomic value that results from evaluating theexpression; or null to indicate that the result is an emptysequence



getCardinality
int getCardinality()(Code)

Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.

This method should always return a result, though it may be the best approximation that is available at the time.

one of the values StaticProperty.ALLOWS_ONE,StaticProperty.ALLOWS_ZERO_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_ONE,StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.EMPTY. This defaultimplementation returns ZERO_OR_MORE (which effectively gives noinformation).



getDependencies
int getDependencies()(Code)
Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.DEPENDS_ON_CONTEXT_ITEM and StaticProperty.DEPENDS_ON_CURRENT_ITEM . The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression. a set of bit-significant flags identifying the dependencies ofthe expression



getImplementationMethod
public int getImplementationMethod()(Code)
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 directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.



getItemType
ItemType getItemType(TypeHierarchy th)(Code)
Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

This method should always return a result, though it may be the best approximation that is available at the time.

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER,Type.NODE, or Type.ITEM (meaning not known at compile time)
Parameters:
  th -



getParentExpression
Container getParentExpression()(Code)
Get the container that immediately contains this expression. This method returns null for an outermost expression; it also return null in the case of literal values. For an XPath expression occurring within an XSLT stylesheet, this method returns the XSLT instruction containing the XPath expression. the expression that contains this expression, if known; return nullif there is no containing expression or if the containing expression is unknown.



getSpecialProperties
int getSpecialProperties()(Code)
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. a set of flags indicating static properties of this expression



iterate
SequenceIterator iterate(XPathContext context) throws XPathException(Code)
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
exception:
  net.sf.saxon.trans.XPathException - if any dynamic error occurs evaluating theexpression
Parameters:
  context - supplies the context for evaluation a SequenceIterator that can be used to iterate over the resultof the expression



iterateSubExpressions
Iterator iterateSubExpressions()(Code)
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions. an iterator containing the sub-expressions of this expression



optimize
Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException(Code)
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.


Parameters:
  opt - the optimizer in use. This provides access to supporting functions; it also allowsdifferent optimization strategies to be used in different circumstances.
Parameters:
  env - the static context of the expression
Parameters:
  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 tonet.sf.saxon.type.Type.ITEM_TYPE
exception:
  net.sf.saxon.trans.StaticError - if an error is discovered during this phase(typically a type error) the original expression, rewritten if appropriate to optimize execution



process
public void process(XPathContext context) throws XPathException(Code)
Process the instruction, without returning any tail calls
Parameters:
  context - The dynamic context, giving access to the current node,the current variables, etc.



promote
Expression promote(PromotionOffer offer) throws XPathException(Code)
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.
Parameters:
  offer - details of the offer, for example the offer to moveexpressions that don't depend on the context to an outer level inthe containing expression
exception:
  net.sf.saxon.trans.XPathException - if any error is detected if the offer is not accepted, return this expression unchanged.Otherwise return the result of rewriting the expression to promotethis subexpression



simplify
Expression simplify(StaticContext env) throws XPathException(Code)
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.
exception:
  net.sf.saxon.trans.StaticError - if an error is discovered during expressionrewriting the simplified expression



typeCheck
Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException(Code)
Perform type checking of an expression and its subexpressions.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.


Parameters:
  env - the static context of the expression
Parameters:
  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 tonet.sf.saxon.type.Type.ITEM_TYPE
exception:
  net.sf.saxon.trans.StaticError - if an error is discovered during this phase(typically a type error) the original expression, rewritten to perform necessaryrun-time type checks, and to perform other type-relatedoptimizations



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