## net.sf.saxon.expr
Class SingletonComparison

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

All Implemented Interfaces:
  Serializable, SourceLocator, LocationProvider, SaxonLocator, ComparisonExpression, EvaluableItem, SequenceIterable, InstructionInfo, Locator

    public class SingletonComparison

extends BinaryExpression
implements ComparisonExpression

Class to handle comparisons of singletons. Unlike ValueComparison, this class converts untyped atomic values to the type of the other argument, and returns false (rather than ()) if either operand is ().

See Also:
  Serialized Form

Field Summary

Fields inherited from class net.sf.saxon.expr.BinaryExpression
`operand0, operand1, operator`

Fields inherited from class net.sf.saxon.expr.Expression
`EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD`

Constructor Summary
`SingletonComparison(Expression p1, int operator, Expression p2, boolean checkTypes)` Create a singleton comparison - that is, a comparison between two singleton (0:1) sequences using the general comparison semantics

Method Summary
`int` `computeCardinality()` Determine the static cardinality.
`boolean` `convertsUntypedToOther()` Determine whether untyped atomic values should be converted to the type of the other operand
`Expression` `copy()` Copy an expression.
`boolean` `effectiveBooleanValue(XPathContext context)` Evaluate the expression in a boolean context
`Item` `evaluateItem(XPathContext context)` Evaluate the expression in a given context
`protected void` `explainExtraAttributes(ExpressionPresenter out)` Add subclass-specific attributes to the expression tree explanation.
`AtomicComparer` `getAtomicComparer()` Get the AtomicComparer used to compare atomic values.
`ItemType` `getItemType(TypeHierarchy th)` Determine the data type of the expression
`int` `getSingletonOperator()` Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE
`boolean` `needsRuntimeComparabilityCheck()` Determine whether a run-time check is needed to check that the types of the arguments are comparable
`void` `setAtomicComparer(AtomicComparer comp)`

Methods inherited from class net.sf.saxon.expr.BinaryExpression
`computeSpecialProperties, displayOperator, equals, explain, getOperands, getOperator, hashCode, isAssociative, isCommutative, isInverse, iterateSubExpressions, optimize, promote, replaceSubExpression, setFlattened, simplify, toString, typeCheck`

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

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

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

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

Constructor Detail

### SingletonComparison

    public SingletonComparison(Expression p1,
                               int operator,
                               Expression p2,
                               boolean checkTypes)

  Create a singleton comparison - that is, a comparison between two singleton (0:1) sequences using the general comparison semantics

  Parameters:
    `p1` - the first operand
    `operator` - the operator
    `p2` - the second operand
    `checkTypes` - true if a run-time check for comparability of the operand types is needed

Method Detail

### setAtomicComparer

    public void setAtomicComparer(AtomicComparer comp)

### getAtomicComparer

    public AtomicComparer getAtomicComparer()

  Description copied from interface: `ComparisonExpression`
  Get the AtomicComparer used to compare atomic values. This encapsulates any collation that is used

  Specified by:
    `getAtomicComparer` in interface `ComparisonExpression`

### getSingletonOperator

    public int getSingletonOperator()

  Description copied from interface: `ComparisonExpression`
  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.

### computeCardinality

    public int computeCardinality()

  Determine the static cardinality. Returns [1..1]

  Overrides:
    `computeCardinality` in class `BinaryExpression`
  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`

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Determine the data type of the expression

  Specified by:
    `getItemType` in class `Expression`
  Parameters:
    `th` - the type hierarchy cache
  Returns:
    Type.BOOLEAN

### copy

    public Expression copy()

  Copy an expression. This makes a deep copy.

  Specified by:
    `copy` in class `Expression`
  Returns:
    the copy of the original expression

### needsRuntimeComparabilityCheck

    public boolean needsRuntimeComparabilityCheck()

  Determine whether a run-time check is needed to check that the types of the arguments are comparable

  Returns:
    true if a run-time check is needed

### evaluateItem

    public Item evaluateItem(XPathContext context)
                      throws XPathException

  Evaluate the expression in a given context

  Specified by:
    `evaluateItem` in interface `EvaluableItem`
  Overrides:
    `evaluateItem` in class `Expression`
  Parameters:
    `context` - the given context for evaluation
  Returns:
    a BooleanValue representing the result of the numeric comparison of the two operands
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

### effectiveBooleanValue

    public boolean effectiveBooleanValue(XPathContext context)
                                  throws XPathException

  Evaluate the expression in a boolean context

  Overrides:
    `effectiveBooleanValue` in class `Expression`
  Parameters:
    `context` - the given context for evaluation
  Returns:
    a boolean representing the result of the numeric comparison of the two operands
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

### explainExtraAttributes

    protected void explainExtraAttributes(ExpressionPresenter out)

  Description copied from class: `BinaryExpression`
  Add subclass-specific attributes to the expression tree explanation. Default implementation does nothing; this is provided for subclasses to override.

  Overrides:
    `explainExtraAttributes` in class `BinaryExpression`
  Parameters:
    `out` - the output destination for the displayed expression tree

Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.