net.sf.saxon.expr
Class BinaryExpression

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

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator

Direct Known Subclasses:

ArithmeticExpression, ArithmeticExpression10, BooleanExpression, GeneralComparison, GeneralComparison10, IdentityComparison, RangeExpression, SingletonComparison, ValueComparison, VennExpression

public abstract class BinaryExpression
extends Expression

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.Expression

EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties

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
protected String	displayOperator() Display the operator used by this binary expression
boolean	equals(Object other) Is this expression the same as another expression?
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
protected void	explainExtraAttributes(ExpressionPresenter out) Add subclass-specific attributes to the expression tree explanation.
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).
Iterator<Expression>	iterateSubExpressions() Get the immediate subexpressions of this expression
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer, Expression parent) Promote this expression if possible
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
void	setFlattened(boolean flattened) Mark an expression as being "flattened".
Expression	simplify(ExpressionVisitor visitor) Simplify an expression
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression.

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, copy, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getItemType, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object

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

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(ExpressionVisitor visitor)
                    throws XPathException

Simplify an expression

Overrides:

simplify in class Expression

Parameters:

visitor - an expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException

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

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

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

optimize

public Expression optimize(ExpressionVisitor visitor,
                           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.

Overrides:

optimize in class Expression

Parameters:

visitor - an expression visitor

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:

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

setFlattened

public void setFlattened(boolean flattened)

Mark an expression as being "flattened". This is a collective term that includes extracting the string value or typed value, or operations such as simple value construction that concatenate text nodes before atomizing. The implication of all of these is that although the expression might return nodes, the identity of the nodes has no significance. This is called during type checking of the parent expression.

Overrides:

setFlattened in class Expression

Parameters:

flattened - set to true if the result of the expression is atomized or otherwise turned into an atomic value

promote

public Expression promote(PromotionOffer offer,
                          Expression parent)
                   throws XPathException

Promote this expression if possible

Overrides:

promote in class 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

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Get the immediate subexpressions of this expression

Overrides:

iterateSubExpressions in class Expression

Returns:

an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

getOperator

public int getOperator()

Get the operator

Returns:

the operator, for example Token.PLUS

getOperands

public Expression[] getOperands()

Get the operands

Returns:

the two operands of the binary expression, as an array of length 2

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 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

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class Expression

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 - the operator, for example Token.PLUS

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))

Parameters:

operator - the operator, for example Token.PLUS

Returns:

true if the operator is associative

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(Object other)

Is this expression the same as another expression?

Overrides:

equals in class Object

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.

Overrides:

hashCode in class Object

toString

public String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:

toString in class Expression

Returns:

a representation of the expression as a string

explain

public void explain(ExpressionPresenter out)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

explain in class Expression

Parameters:

out - the output destination for the displayed expression tree

explainExtraAttributes

protected void explainExtraAttributes(ExpressionPresenter out)

Add subclass-specific attributes to the expression tree explanation. Default implementation does nothing; this is provided for subclasses to override.

Parameters:

out - the output destination for the displayed expression tree

displayOperator

protected String displayOperator()

Display the operator used by this binary expression

Returns:

String representation of the operator (for diagnostic display only)