net.sf.saxon.expr
Class BinaryExpression

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.BinaryExpression

All Implemented Interfaces:

Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

Direct Known Subclasses:

net.sf.saxon.expr.ArithmeticExpression, BooleanExpression, GeneralComparison, GeneralComparison10, IdentityComparison, RangeExpression, SingletonComparison, ValueComparison, VennExpression

public abstract class BinaryExpression

extends ComputedExpression

Binary Expression: a numeric or boolean expression consisting of the two operands and an operator

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

BinaryExpression(Expression p0, int op, Expression p1)
Create a binary expression identifying the two operands and the operator

Method Summary

int	computeCardinality() Determine the static cardinality.
int	computeSpecialProperties() Determine the special properties of this expression
void	display(int level, NamePool pool, java.io.PrintStream out) Diagnostic print of expression structure
protected java.lang.String	displayOperator()
boolean	equals(java.lang.Object other) Is this expression the same as another expression?
Expression[]	getOperands() Get the operands
int	getOperator() Get the operator
int	hashCode() Get a hashCode for comparing two expressions.
protected static boolean	isAssociative(int operator) Determine whether an operator is associative, that is, ((a^b)^c) = (a^(b^c))
protected static boolean	isCommutative(int operator) Determine whether a binary operator is commutative, that is, A op B = B op A.
protected static boolean	isInverse(int op1, int op2) Test if one operator is the inverse of another, so that (A op1 B) is equivalent to (B op2 A).
java.util.Iterator	iterateSubExpressions() Get the immediate subexpressions of this expression
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer) Promote this expression if possible
Expression	simplify(StaticContext env) Simplify an expression
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression.

Methods inherited from class net.sf.saxon.expr.ComputedExpression

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface net.sf.saxon.expr.Expression

getItemType

Field Detail

operand0

protected Expression operand0

operand1

protected Expression operand1

operator

protected int operator

Constructor Detail

BinaryExpression

public BinaryExpression(Expression p0,
                        int op,
                        Expression p1)

Create a binary expression identifying the two operands and the operator

Parameters:

p0 - the left-hand operand

op - the operator, as a token returned by the Tokenizer (e.g. Token.AND)

p1 - the right-hand operand

Method Detail

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

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression. Default implementation for binary operators that accept any kind of operand

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

Throws:

XPathException

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           ItemType contextItemType)
                    throws XPathException

Perform optimisation of an expression and its subexpressions.

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.

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

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 if appropriate to optimize execution

Throws:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

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

getOperator

public int getOperator()

Get the operator

getOperands

public Expression[] getOperands()

Get the operands

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

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class ComputedExpression

Returns:

StaticProperty.NON_CREATIVE. This is overridden for some subclasses.

isCommutative

protected static boolean isCommutative(int operator)

Determine whether a binary operator is commutative, that is, A op B = B op A.

Parameters:

operator -

Returns:

true if the operator is commutative

isAssociative

protected static boolean isAssociative(int operator)

Determine whether an operator is associative, that is, ((a^b)^c) = (a^(b^c))

isInverse

protected static boolean isInverse(int op1,
                                   int op2)

Test if one operator is the inverse of another, so that (A op1 B) is equivalent to (B op2 A). Commutative operators are the inverse of themselves and are therefore not listed here.

Parameters:

op1 - the first operator

op2 - the second operator

Returns:

true if the operators are the inverse of each other

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

hashCode

public int hashCode()

Get a 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.

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()