net.sf.saxon.expr

Class BooleanExpression

public class BooleanExpression extends BinaryExpression implements Negatable

Boolean expression: two truth values combined using AND or OR.
Constructor Summary
BooleanExpression(Expression p1, int operator, Expression p2)
Construct a boolean expression
Method Summary
intcomputeCardinality()
Determine the static cardinality.
Expressioncopy()
Copy an expression.
booleaneffectiveBooleanValue(XPathContext c)
Evaluate as a boolean.
ItemevaluateItem(XPathContext context)
Evaluate the expression
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the expression
booleanisNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable
static voidlistAndComponents(Expression exp, List list)
Construct a list containing the "anded" subexpressions of an expression: if the expression is (A and B and C), this returns (A, B, C).
Expressionnegate()
Return the negation of this boolean expression, that is, an expression that returns true when this expression returns false, and vice versa
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)

Constructor Detail

BooleanExpression

public BooleanExpression(Expression p1, int operator, Expression p2)
Construct a boolean expression

Parameters: p1 the first operand operator one of AND or OR p2 the second operand

Method Detail

computeCardinality

public int computeCardinality()
Determine the static cardinality. Returns [1..1]

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext c)
Evaluate as a boolean.

evaluateItem

public Item evaluateItem(XPathContext context)
Evaluate the expression

getItemType

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

Parameters: th the type hierarchy cache

Returns: BuiltInAtomicType.BOOLEAN

isNegatable

public boolean isNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable

Returns: true if it is

listAndComponents

public static void listAndComponents(Expression exp, List list)
Construct a list containing the "anded" subexpressions of an expression: if the expression is (A and B and C), this returns (A, B, C).

Parameters: exp the expression to be decomposed list the list to which the subexpressions are to be added.

negate

public Expression negate()
Return the negation of this boolean expression, that is, an expression that returns true when this expression returns false, and vice versa

Returns: the negation 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)

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)