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java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.TailExpression
public class TailExpression
extends Expression
Field Summary |
Fields inherited from class net.sf.saxon.expr.Expression | |
EVALUATE_METHOD , ITERATE_METHOD , PROCESS_METHOD , locationId , staticProperties |
Constructor Summary | |
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Method Summary | |
int |
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int |
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Expression |
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boolean |
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void |
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Expression |
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ItemType |
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int |
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int |
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SequenceIterator |
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Iterator |
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Expression |
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Expression |
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boolean |
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Expression |
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public TailExpression(Expression base, int start)
Construct a TailExpression, representing a filter expression of the form $base[position() >= $start]
- Parameters:
base
- the expression to be filteredstart
- the position (1-based) of the first item to be included
public int computeCardinality()
Compute the static cardinality of this expression
- Overrides:
- computeCardinality in interface Expression
- 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
public int computeSpecialProperties()
Compute the special properties of this expression. These properties are denoted by a bit-significant integer, possible values are in classStaticProperty
. The "special" properties are properties other than cardinality and dependencies, and most of them relate to properties of node sequences, for example whether the nodes are in document order.
- Overrides:
- computeSpecialProperties in interface Expression
- Returns:
- the special properties, as a bit-significant integer
public Expression copy()
Copy an expression. This makes a deep copy.
- Overrides:
- copy in interface Expression
- Returns:
- the copy of the original expression
public boolean equals(Object other)
Compare two expressions to see if they are equal
- Parameters:
other
- the other expression
- Returns:
- true if the expressions are equivalent
public void explain(ExpressionPresenter destination)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
- Overrides:
- explain in interface Expression
public Expression getBaseExpression()
Get the base expression (of which this expression returns the tail part of the value)
- Returns:
- the base expression
public ItemType getItemType(TypeHierarchy th)
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.
- Overrides:
- getItemType in interface Expression
- Parameters:
th
- the type hierarchy cache
- Returns:
- a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)
public int getStart()
Get the start offset
- Returns:
- the one-based start offset (returns 2 if all but the first item is being selected)
public int hashCode()
public 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.
- Specified by:
- iterate in interface SequenceIterable
- Overrides:
- iterate in interface 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
public Iterator iterateSubExpressions()
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.
- Overrides:
- iterateSubExpressions in interface Expression
- Returns:
- an iterator containing the sub-expressions of this expression
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException
Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization. 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 interface Expression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
public 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.
- Overrides:
- promote in interface 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
public boolean replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
- Overrides:
- replaceSubExpression in interface Expression
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression
- Returns:
- true if the original subexpression is found
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException
Perform type checking of an expression and its subexpressions. This is the second phase of static optimization. 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. If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.
- Overrides:
- typeCheck in interface Expression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)