net.sf.saxon.expr

Class CompareToConstant

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.UnaryExpression

net.sf.saxon.expr.CompareToConstant

All Implemented Interfaces:

ComparisonExpression, ExportAgent, Locatable, IdentityComparable, Traceable

Direct Known Subclasses:

CompareToIntegerConstant, CompareToStringConstant

public abstract class CompareToConstant
extends UnaryExpression
implements ComparisonExpression

This class implements a comparison of a computed value to a literal 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. Different subclasses handle different types of constant.

Field Summary

Fields

Modifier and Type	Field and Description
protected int	operator

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
CompareToConstant(Expression p0)

Method Summary

Modifier and Type	Method and Description
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
boolean	convertsUntypedToOther() Determine whether untyped atomic values should be converted to the type of the other operand
BooleanValue	evaluateItem(XPathContext context) Evaluate an expression as a single item.
int	getComparisonOperator() Get the comparison operator
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemType	getItemType() Determine the data type of the expression, if possible.
Operand	getLhs() Get the two operands of the comparison
Expression	getLhsExpression()
protected OperandRole	getOperandRole() Get the usage (in terms of streamability analysis) of the single operand
Operand	getRhs()
abstract Expression	getRhsExpression()
int	getSingletonOperator() Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform optimisation of an expression and its subexpressions.

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

computeCardinality, computeHashCode, displayOperator, emitExtraAttributes, equals, export, getBaseExpression, getOperand, operands, setBaseExpression, toShortString, toString, typeCheck

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

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, copy, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExpressionName, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getStreamerName, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, typeCheckChildren, typeError, unordered, verifyParentPointers

Methods inherited from class java.lang.Object

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

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

getAtomicComparer

Methods inherited from interface net.sf.saxon.trace.Traceable

gatherProperties

Field Detail

operator

protected int operator

Constructor Detail

CompareToConstant

public CompareToConstant(Expression p0)

Method Detail

getOperandRole

protected OperandRole getOperandRole()

Description copied from class: UnaryExpression

Get the usage (in terms of streamability analysis) of the single operand

Specified by:

getOperandRole in class UnaryExpression

Returns:

the operand usage

getLhsExpression

public Expression getLhsExpression()

Specified by:

getLhsExpression in interface ComparisonExpression

getLhs

public Operand getLhs()

Description copied from interface: ComparisonExpression

Get the two operands of the comparison

Specified by:

getLhs in interface ComparisonExpression

getRhsExpression

public abstract Expression getRhsExpression()

Specified by:

getRhsExpression in interface ComparisonExpression

getRhs

public Operand getRhs()

Specified by:

getRhs in interface ComparisonExpression

getComparisonOperator

public int getComparisonOperator()

Get the comparison operator

Returns:

one of Token.FEQ, Token.FNE, Token.FGE, Token.FGT, Token.FLE, Token.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.

Specified by:

getImplementationMethod in class Expression

Returns:

the value Expression.EVALUATE_METHOD

computeSpecialProperties

public int computeSpecialProperties()

Description copied from class: UnaryExpression

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:

computeSpecialProperties in class UnaryExpression

Returns:

the special properties, as a bit-significant integer

evaluateItem

public BooleanValue evaluateItem(XPathContext context)
                          throws XPathException

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.

Overrides:

evaluateItem in class Expression

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:

XPathException - if any dynamic error occurs evaluating the expression

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ContextItemStaticInfo contextInfo)
                    throws XPathException

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.

Overrides:

optimize in class UnaryExpression

Parameters:

visitor - the expression visitor

contextInfo - 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)

getItemType

public ItemType getItemType()

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.

Overrides:

getItemType in class UnaryExpression

Returns:

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

getSingletonOperator

public int getSingletonOperator()

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

Specified by:

getSingletonOperator in interface ComparisonExpression

convertsUntypedToOther

public boolean convertsUntypedToOther()

Determine whether untyped atomic values should be converted to the type of the other operand

Specified by:

convertsUntypedToOther in interface ComparisonExpression

Returns:

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