Class Expression
- java.lang.Object
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- org.apache.commons.jxpath.ri.compiler.Expression
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- Direct Known Subclasses:
Constant
,Operation
,Path
,VariableReference
public abstract class Expression extends java.lang.Object
Common superclass for several types of nodes in the parse tree. Provides APIs for optimization of evaluation of expressions. Specifically, an expression only needs to executed once during the evaluation of an xpath if that expression is context-independent. Expression.isContextDependent() provides that hint.- Version:
- $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
Expression.PointerIterator
Pointer iteratorstatic class
Expression.ValueIterator
Value Iterator
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Field Summary
Fields Modifier and Type Field Description private boolean
contextDependencyKnown
private boolean
contextDependent
protected static java.lang.Double
NOT_A_NUMBER
NaNprotected static java.lang.Double
ONE
oneprotected static java.lang.Double
ZERO
zero
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Constructor Summary
Constructors Constructor Description Expression()
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract java.lang.Object
compute(EvalContext context)
Evaluates the expression.abstract boolean
computeContextDependent()
Implemented by subclasses and result is cached by isContextDependent()abstract java.lang.Object
computeValue(EvalContext context)
Evaluates the expression.boolean
isContextDependent()
Returns true if this expression should be re-evaluated each time the current position in the context changes.java.util.Iterator
iterate(EvalContext context)
Iterate over the values from the specified context.java.util.Iterator
iteratePointers(EvalContext context)
Iterate over the pointers from the specified context.
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Field Detail
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ZERO
protected static final java.lang.Double ZERO
zero
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ONE
protected static final java.lang.Double ONE
one
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NOT_A_NUMBER
protected static final java.lang.Double NOT_A_NUMBER
NaN
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contextDependencyKnown
private boolean contextDependencyKnown
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contextDependent
private boolean contextDependent
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Method Detail
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isContextDependent
public boolean isContextDependent()
Returns true if this expression should be re-evaluated each time the current position in the context changes.- Returns:
- boolean
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computeContextDependent
public abstract boolean computeContextDependent()
Implemented by subclasses and result is cached by isContextDependent()- Returns:
- calculated context-dependentness as boolean
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computeValue
public abstract java.lang.Object computeValue(EvalContext context)
Evaluates the expression. If the result is a node set, returns the first element of the node set.- Parameters:
context
- evaluation context- Returns:
- Object
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compute
public abstract java.lang.Object compute(EvalContext context)
Evaluates the expression. If the result is a node set, returns the first element of the node set.- Parameters:
context
- evaluation context- Returns:
- Object
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iterate
public java.util.Iterator iterate(EvalContext context)
Iterate over the values from the specified context.- Parameters:
context
- evaluation context- Returns:
- value Iterator
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iteratePointers
public java.util.Iterator iteratePointers(EvalContext context)
Iterate over the pointers from the specified context.- Parameters:
context
- evaluation context- Returns:
- pointer Iterator
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