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java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.IsLastExpression
public final class IsLastExpression
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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Item |
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void |
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boolean |
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int |
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ItemType |
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Expression |
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Expression |
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public IsLastExpression(boolean condition)
Construct a condition that tests position() eq last() (if condition is true) or position() ne last() (if condition is false).
- Parameters:
condition
- true if we are testing "equals", false for "not equals".
public int computeCardinality()
Determine the static cardinality
- Overrides:
- computeCardinality in interface Expression
public int computeSpecialProperties()
Determine the special properties of this expression
- Overrides:
- computeSpecialProperties in interface Expression
- Returns:
StaticProperty.NON_CREATIVE
.
public Expression copy()
Copy an expression. This makes a deep copy.
- Overrides:
- copy in interface Expression
- Returns:
- the copy of the original expression
public Item evaluateItem(XPathContext c) 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.
- Specified by:
- evaluateItem in interface EvaluableItem
- Overrides:
- evaluateItem in interface Expression
- Parameters:
- 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
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 boolean getCondition()
Get the condition we are testing for
- Returns:
- true if we are testing "equals", false for "not equals".
public int getIntrinsicDependencies()
Get the dependencies of this expression on the context
- Overrides:
- getIntrinsicDependencies in interface Expression
public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression
- Overrides:
- getItemType in interface Expression
- Parameters:
th
- the type hierarchy cache
- Returns:
- Type.BOOLEAN
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
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
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
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