| net.sf.saxon.expr.Expression
All known Subclasses: net.sf.saxon.value.Value, net.sf.saxon.expr.ComputedExpression, net.sf.saxon.pattern.PatternSponsor,
| Expression | | public interface Expression extends Serializable(Code) | | Interface supported by an XPath expression. This includes both compile-time
and run-time methods.
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| Method Summary | |
| public void | checkPermittedContents(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 void | display(int level, NamePool pool, PrintStream out)
Diagnostic print of expression structure. | | boolean | effectiveBooleanValue(XPathContext context)
Get the effective boolean value of the expression. | | public String | evaluateAsString(XPathContext context)
Evaluate an expression as a String. | | Item | evaluateItem(XPathContext context)
Evaluate an expression as a single item. | | int | getCardinality()
Determine the static cardinality of the expression. | | int | getDependencies()
Determine which aspects of the context the expression depends on. | | 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 directly. | | ItemType | getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible. | | Container | getParentExpression()
Get the container that immediately contains this expression. | | int | getSpecialProperties()
Get the static properties of this expression (other than its type). | | SequenceIterator | iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence. | | Iterator | iterateSubExpressions()
Get the immediate sub-expressions of this expression. | | Expression | optimize(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 void | process(XPathContext context)
| | Expression | promote(PromotionOffer offer)
Offer promotion for this subexpression. | | Expression | simplify(StaticContext env)
Simplify an expression. | | Expression | typeCheck(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. |
| 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) | | |
| 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 |
| 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.
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| 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 |
| 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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