net.sf.saxon.expr
Class IdentityComparison

java.lang.Object
  |
  +--net.sf.saxon.expr.ComputedExpression
        |
        +--net.sf.saxon.expr.BinaryExpression
              |
              +--net.sf.saxon.expr.IdentityComparison
All Implemented Interfaces:
Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

public final class IdentityComparison
extends net.sf.saxon.expr.BinaryExpression

IdentityComparison: a boolean expression that compares two nodes for equals, not-equals, greater-than or less-than based on identity and document ordering

See Also:
Serialized Form

Field Summary
protected  Expression operand0
           
protected  Expression operand1
           
protected  int operator
           
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
 
Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
IdentityComparison(Expression p1, int op, Expression p2)
          Create an identity comparison identifying the two operands and the operator
 
Method Summary
 Expression analyze(StaticContext env, ItemType contextItemType)
          Type-check the expression
 int computeCardinality()
          Determine the static cardinality.
 void display(int level, NamePool pool, java.io.PrintStream out)
          Diagnostic print of expression structure
protected  java.lang.String displayOperator()
           
 boolean effectiveBooleanValue(XPathContext context)
          Get the effective boolean value of the expression.
 boolean equals(java.lang.Object other)
          Is this expression the same as another expression?
 Item evaluateItem(XPathContext context)
          Evaluate the expression
 ItemType getItemType()
          Determine the data type of the expression
 int hashCode()
          get HashCode for comparing two expressions.
protected static boolean isCommutative(int operator)
           
 java.util.Iterator iterateSubExpressions()
          Get the immediate subexpressions of this expression
 Expression promote(PromotionOffer offer)
          Promote this expression if possible
 void setGenerateIdEmulation(boolean flag)
          Set flag to indicate different empty-sequence behavior when emulating comparison of two generate-id's
 Expression simplify(StaticContext env)
          Simplify an expression
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, computeDependencies, computeSpecialProperties, computeStaticProperties, dynamicError, dynamicError, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getParentExpression, getPublicId, getSpecialProperties, getSystemId, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, typeError
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

operand0

protected Expression operand0

operand1

protected Expression operand1

operator

protected int operator
Constructor Detail

IdentityComparison

public IdentityComparison(Expression p1,
                          int op,
                          Expression p2)
Create an identity comparison identifying the two operands and the operator

Parameters:
p1 - the left-hand operand
op - the operator, as a token returned by the Tokenizer (e.g. Token.LT)
p2 - the right-hand operand
Method Detail

setGenerateIdEmulation

public void setGenerateIdEmulation(boolean flag)
Set flag to indicate different empty-sequence behavior when emulating comparison of two generate-id's


analyze

public Expression analyze(StaticContext env,
                          ItemType contextItemType)
                   throws XPathException
Type-check the expression

Specified by:
analyze in interface Expression
Overrides:
analyze in class net.sf.saxon.expr.BinaryExpression
Parameters:
env - the static context of the expression
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 to Type.ITEM_TYPE
Returns:
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
XPathException

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Evaluate the expression

Specified by:
evaluateItem in interface Expression
Overrides:
evaluateItem in class ComputedExpression
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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException
Description copied from class: ComputedExpression
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.

Specified by:
effectiveBooleanValue in interface Expression
Overrides:
effectiveBooleanValue in class ComputedExpression
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

getItemType

public ItemType getItemType()
Determine the data type of the expression

Returns:
Type.BOOLEAN

simplify

public Expression simplify(StaticContext env)
                    throws XPathException
Simplify an expression

Specified by:
simplify in interface Expression
Overrides:
simplify in class ComputedExpression
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException
Promote this expression if possible

Specified by:
promote in interface Expression
Overrides:
promote in class ComputedExpression
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

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()
Get the immediate subexpressions of this expression

Specified by:
iterateSubExpressions in interface Expression
Overrides:
iterateSubExpressions in class ComputedExpression
Returns:
an iterator containing the sub-expressions of this expression

computeCardinality

public int computeCardinality()
Determine the static cardinality. Default implementation returns [0..1] if either operand can be empty, or [1..1] otherwise.

Specified by:
computeCardinality in class ComputedExpression

isCommutative

protected static boolean isCommutative(int operator)

equals

public boolean equals(java.lang.Object other)
Is this expression the same as another expression?

Overrides:
equals in class java.lang.Object

hashCode

public int hashCode()
get HashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.

Overrides:
hashCode in class java.lang.Object

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)
Diagnostic print of expression structure

Parameters:
level - indentation level for this expression
pool - NamePool used to expand any names appearing in the expression
out - Output destination

displayOperator

protected java.lang.String displayOperator()