net.sf.saxon.expr
Interface Expression
- All Known Implementing Classes:
- Adjust, Aggregate, AnyURIValue, AppendExpression, ArithmeticExpression, ArithmeticExpression.DateAndDuration, ArithmeticExpression.DateDifference, ArithmeticExpression.DurationAddition, ArithmeticExpression.DurationMultiplication, ArithmeticExpression.NumericArithmetic, Assignation, AtomicSequenceConverter, AtomicUserDefinedValue, AtomicValue, Atomizer, Attribute, AttributeReference, Available, AxisExpression, Base64BinaryValue, BaseURI, BinaryExpression, BooleanExpression, BooleanFn, BooleanValue, CalendarValue, CardinalityChecker, CastableExpression, CastAsQName, CastExpression, Closure, CollatingFunction, Collection, Comment, Compare, CompileTimeFunction, Component, ComputedExpression, Concat, Contains, ContextItemExpression, ConvertToString, Copy, CopyOf, Current, CurrentDateTime, CurrentGroup, Data, DateTimeValue, DateValue, DecimalValue, DeepEqual, DefaultCollation, DistinctValues, Doc, Document, DocumentInstr, DocumentSorter, DoubleValue, DurationValue, Element, ElementCreator, EmptySequence, Error, ErrorExpression, EscapeURI, Evaluate, Existence, ExprInstruction, FilterExpression, FirstItemExpression, FixedAttribute, FixedElement, FloatValue, ForceCase, ForExpression, FormatDate, FormatNumber, FormatNumber2, FunctionCall, FunctionProxy, GDayValue, GeneralComparison, GMonthDayValue, GMonthValue, GYearMonthValue, GYearValue, HexBinaryValue, Id, IdentityComparison, Idref, IfExpression, IndexOf, InScopeNamespaces, Insert, InstanceOfExpression, IntegerRangeTest, IntegerValue, IsLastExpression, ItemChecker, Key, Lang, Last, LetExpression, Matches, Minimax, MinimaxComparison, MonthDurationValue, NamePart, Namespace, NamespaceForPrefix, NormalizeSpace, NumberFn, NumericValue, ObjectValue, ParentNodeExpression, Parse, PathExpression, Position, PositionRange, ProcessingInstruction, QNameFn, QNameValue, QuantifiedExpression, RangeExpression, RegexGroup, Remove, Replace, ResolveQName, ResolveURI, RestrictedStringValue, Reverse, Reverser, Root, RootExpression, Rounding, SecondsDurationValue, Sequence, SequenceExtent, SequenceIntent, SequenceValue, Serialize, SimpleNodeConstructor, SingleNodeExpression, SingletonComparison, SingletonNode, SortExpression, StringFn, StringJoin, StringLength, StringValue, Subsequence, Substring, SuppliedParameterReference, SystemFunction, SystemProperty, TailExpression, Text, TimeValue, Tokenize, Trace, Translate, TreatFn, TupleExpression, TupleSorter, TypeExpression, Unicode, Unordered, UnparsedEntity, UnparsedText, UntypedAtomicConverter, UntypedAtomicValue, UserFunctionCall, Value, ValueComparison, ValueOf, VariableReference, VennExpression
public interface Expression
Interface supported by an XPath expression. This includes both compile-time
and run-time methods.
simplify
Expression simplify()
throws XPathException
- Simplify an expression. This performs any static optimization (by rewriting the expression
as a different expression). The default implementation does nothing.
- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression
rewriting
analyze
Expression analyze(StaticContext env)
throws XPathException
- Perform static analysis 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 will only be accurately known if they have been explicitly declared.
- Parameters:
env
- the static context of the expression
- 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)
promote
Expression promote(PromotionOffer offer)
throws XPathException
- 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 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
getSpecialProperties
int getSpecialProperties()
- 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:
- a set of flags indicating static properties of this expression
getCardinality
int getCardinality()
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.
- Returns:
- one of the values Cardinality.ONE_OR_MORE,
Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE,
Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default
implementation returns ZERO_OR_MORE (which effectively gives no
information).
getItemType
ItemType getItemType()
- 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.
- Returns:
- a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER,
Type.NODE, or Type.ITEM (meaning not known at compile time)
getDependencies
int getDependencies()
- Determine which aspects of the context the expression depends on. The result is
a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and
XPathContext.CURRENT_NODE. 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.
- Returns:
- a set of bit-significant flags identifying the dependencies of
the expression
getSubExpressions
Expression[] getSubExpressions()
- Get the immediate sub-expressions of this expression. Default implementation
returns a zero-length array, appropriate for an expression that has no
sub-expressions.
- Returns:
- an array containing the sub-expressions of this expression
evaluateItem
Item evaluateItem(XPathContext context)
throws XPathException
- 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
- 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
iterate
SequenceIterator iterate(XPathContext context)
throws XPathException
- 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.
- 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
effectiveBooleanValue
boolean effectiveBooleanValue(XPathContext context)
throws XPathException
- 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
- Returns:
- the effective boolean value
- Throws:
XPathException
- if any dynamic error occurs evaluating the
expression
evaluateAsString
String evaluateAsString(XPathContext context)
throws XPathException
- 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.
- Parameters:
context
- The context in which the expression is to be evaluated
- Returns:
- the value of the expression, evaluated in the current context.
The expression must return a string or (); if the value of the
expression is (), this method returns "".
- Throws:
XPathException
- if any dynamic error occurs evaluating the
expression
ClassCastException
- if the result type of the
expression is not xs:string?
display
void display(int level,
NamePool pool)
- Diagnostic print of expression structure. The expression is written to the System.err
output stream
- Parameters:
level
- indentation level for this expression