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## com.saxonica.expr
Class EquivalenceComparison

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.expr.BinaryExpression
              com.saxonica.expr.EquivalenceComparison

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

    public class EquivalenceComparison

extends BinaryExpression
implements ComparisonExpression

Class to handle equivalence comparisons of singletons. This only handles equality comparison. It follows the rules used for grouping and for XQuery 1.1 switch expressions: - each operand must be zero or one atomic values - untypedAtomic is treated as string - non-comparable values are not equal (no type errors) - two empty sequences are equal to each other - two NaN values are equal to each other

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
`EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD`

Constructor Summary
`EquivalenceComparison(Expression p1, int operator, Expression p2)` 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.
`AtomicComparer` | `getComparer()`
`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` | `isKnownToBeComparable()`
`Expression` | `typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)` Type-check the expression.

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

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, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, 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

### EquivalenceComparison

    public EquivalenceComparison(Expression p1,
                                 int operator,
                                 Expression p2)

  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

Method Detail

### typeCheck

    public Expression typeCheck(ExpressionVisitor visitor,
                                ExpressionVisitor.ContextItemType contextItemType)
                         throws XPathException

  Type-check the expression. Default implementation for binary operators that accept any kind of operand

  Overrides:
    `typeCheck` in class `BinaryExpression`
  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 `Type.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)

### 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

### isKnownToBeComparable

    public boolean isKnownToBeComparable()

### getComparer

    public AtomicComparer getComparer()

### 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

### evaluateItem

    public Item evaluateItem(XPathContext context)
                      throws XPathException

  Evaluate the expression in a given context

  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

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Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.