net.sf.saxon.expr

Class BinaryExpression

public abstract class BinaryExpression extends Expression

Binary Expression: a numeric or boolean expression consisting of the two operands and an operator
Field Summary
protected Expressionoperand0
protected Expressionoperand1
protected intoperator
Constructor Summary
BinaryExpression(Expression p0, int op, Expression p1)
Create a binary expression identifying the two operands and the operator
Method Summary
intcomputeCardinality()
Determine the static cardinality.
intcomputeSpecialProperties()
Determine the special properties of this expression
protected StringdisplayOperator()
Display the operator used by this binary expression
booleanequals(Object other)
Is this expression the same as another expression?
voidexplain(ExpressionPresenter out)
Diagnostic print of expression structure.
protected voidexplainExtraAttributes(ExpressionPresenter out)
Add subclass-specific attributes to the expression tree explanation.
Expression[]getOperands()
Get the operands
intgetOperator()
Get the operator
inthashCode()
Get a hashCode for comparing two expressions.
protected static booleanisAssociative(int operator)
Determine whether an operator is associative, that is, ((a^b)^c) = (a^(b^c))
protected static booleanisCommutative(int operator)
Determine whether a binary operator is commutative, that is, A op B = B op A.
protected static booleanisInverse(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
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expressionpromote(PromotionOffer offer, Expression parent)
Promote this expression if possible
booleanreplaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
voidsetFlattened(boolean flattened)
Mark an expression as being "flattened".
Expressionsimplify(ExpressionVisitor visitor)
Simplify an expression
StringtoString()
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.
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression.

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

computeCardinality

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

computeSpecialProperties

public int computeSpecialProperties()
Determine the special properties of this expression

Returns: NON_CREATIVE. This is overridden for some subclasses.

displayOperator

protected String displayOperator()
Display the operator used by this binary expression

Returns: String representation of the operator (for diagnostic display only)

equals

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

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

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

getOperands

public Expression[] getOperands()
Get the operands

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

getOperator

public int getOperator()
Get the operator

Returns: the operator, for example PLUS

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.

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 PLUS

Returns: true if the operator is associative

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 PLUS

Returns: true if the operator is commutative

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

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()
Get the immediate subexpressions of this expression

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
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: 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 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)

promote

public Expression promote(PromotionOffer offer, Expression parent)
Promote this expression if possible

replaceSubExpression

public boolean replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression

Parameters: original the original subexpression replacement the replacement subexpression

Returns: true if the original subexpression is found

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.

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

simplify

public Expression simplify(ExpressionVisitor visitor)
Simplify an expression

Parameters: visitor an expression visitor

Returns: the simplified expression

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

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression. Default implementation for binary operators that accept any kind of operand