net.sf.saxon.expr

Class CompareToIntegerConstant

public class CompareToIntegerConstant extends Expression implements ComparisonExpression

This class implements a comparison of a numeric value to an integer constant using one of the operators eq, ne, lt, gt, le, ge. The semantics are identical to ValueComparison, but this is a fast path for an important common case.
Constructor Summary
CompareToIntegerConstant(Expression operand, int operator, long comparand)
Create the expression
Method Summary
protected intcomputeCardinality()
intcomputeDependencies()
Compute the dependencies of an expression, as the union of the dependencies of its subexpressions.
intcomputeSpecialProperties()
booleanconvertsUntypedToOther()
Determine whether untyped atomic values should be converted to the type of the other operand
Expressioncopy()
Copy an expression.
booleaneffectiveBooleanValue(XPathContext context)
Get the effective boolean value of the expression.
ItemevaluateItem(XPathContext context)
Evaluate an expression as a single item.
voidexplain(ExpressionPresenter destination)
Diagnostic print of expression structure.
AtomicComparergetAtomicComparer()
Get the AtomicComparer used to compare atomic values.
longgetComparand()
Get the integer value on the rhs of the expression
intgetComparisonOperator()
Get the comparison operator
intgetImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the expression, if possible.
ExpressiongetOperand()
Get the expression on the lhs of the comparison
Expression[]getOperands()
Get the two operands of the comparison
intgetSingletonOperator()
Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE
Iterator<Expression>iterateSubExpressions()
Get the immediate sub-expressions of this expression.
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expressionpromote(PromotionOffer offer, Expression parent)
Offer promotion for this subexpression.
booleanreplaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
Expressionsimplify(ExpressionVisitor visitor)
Simplify an expression.
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Perform type checking of an expression and its subexpressions.

Constructor Detail

CompareToIntegerConstant

public CompareToIntegerConstant(Expression operand, int operator, long comparand)
Create the expression

Parameters: operand the operand to be compared with an integer constant operator the comparison operator, one of FEQ, FNE, FGE, FGT, FLE, FLT comparand the integer constant

Method Detail

computeCardinality

protected int computeCardinality()

computeDependencies

public int computeDependencies()
Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.

Returns: the depencies, as a bit-mask

computeSpecialProperties

public int computeSpecialProperties()

convertsUntypedToOther

public boolean convertsUntypedToOther()
Determine whether untyped atomic values should be converted to the type of the other operand

Returns: true if untyped values should be converted to the type of the other operand, false if they should be converted to strings.

copy

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

Returns: the copy of the original expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
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.

Parameters: context The context in which the expression is to be evaluated

Returns: the effective boolean value

Throws: net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the expression

evaluateItem

public Item evaluateItem(XPathContext context)
Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

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: net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the expression

explain

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

getAtomicComparer

public AtomicComparer getAtomicComparer()
Get the AtomicComparer used to compare atomic values. This encapsulates any collation that is used

getComparand

public long getComparand()
Get the integer value on the rhs of the expression

Returns: the integer constant

getComparisonOperator

public int getComparisonOperator()
Get the comparison operator

Returns: one of FEQ, FNE, FGE, FGT, FLE, FLT

getImplementationMethod

public int getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.

Returns: the value CompareToIntegerConstant

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

This method should always return a result, though it may be the best approximation that is available at the time.

Parameters: th the type hierarchy cache

Returns: a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

getOperand

public Expression getOperand()
Get the expression on the lhs of the comparison

Returns: the left hand operand

getOperands

public Expression[] getOperands()
Get the two operands of the comparison

Returns: the two operands

getSingletonOperator

public int getSingletonOperator()
Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Returns: an iterator containing the sub-expressions of this expression

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

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 the 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)
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

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 parent

Returns: if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws: net.sf.saxon.trans.XPathException if any error is detected

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

simplify

public Expression simplify(ExpressionVisitor visitor)
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Parameters: visitor the expression visitor

Returns: the simplified expression

Throws: XPathException if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Parameters: visitor the 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 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)