Package net.sf.saxon.expr

## Class ValueComparison

- java.lang.Object
- - net.sf.saxon.expr.Expression
  - - net.sf.saxon.expr.BinaryExpression
    - - net.sf.saxon.expr.ValueComparison

- All Implemented Interfaces:
    `ComparisonExpression`, `ExportAgent`, `Locatable`, `Negatable`, `IdentityComparable`, `Traceable`

      public final class ValueComparison
      extends BinaryExpression
      implements ComparisonExpression, Negatable

  ValueComparison: a boolean expression that compares two atomic values for equals, not-equals, greater-than or less-than. Implements the operators eq, ne, lt, le, gt, ge

- - ### Field Summary

    - ### Fields inherited from class net.sf.saxon.expr.BinaryExpression

      `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 | Description
    --- | ---
    `ValueComparison​(Expression p1, int op, Expression p2)` | Create a comparison expression identifying the two operands and the operator

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `static boolean` | `compare​(AtomicValue v0, int op, AtomicValue v1, AtomicComparer comparer, boolean checkTypes)` | Compare two atomic values, using a specified operator and collation
    `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​(RebindingMap rebindings)` | Copy an expression.
    `boolean` | `effectiveBooleanValue​(XPathContext context)` | Evaluate the effective boolean value of the expression
    `boolean` | `equals​(java.lang.Object other)` | Is this expression the same as another expression?
    `BooleanValue` | `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.
    `java.lang.String` | `getExpressionName()` | Get a name identifying the kind of expression, in terms meaningful to a user.
    `ItemType` | `getItemType()` | Determine the data type of the expression
    `BooleanValue` | `getResultWhenEmpty()` | Get the result to be returned if one of the operands is an empty sequence
    `int` | `getSingletonOperator()` | Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE
    `UType` | `getStaticUType​(UType contextItemType)` | Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
    `boolean` | `isNegatable​(TypeHierarchy th)` | Check whether this specific instance of the expression is negatable
    `boolean` | `needsRuntimeComparabilityCheck()` | Determine whether a run-time check is needed to check that the types of the arguments are comparable
    `Expression` | `negate()` | Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false().
    `Expression` | `optimize​(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` | Perform optimisation of an expression and its subexpressions.
    `void` | `setAtomicComparer​(AtomicComparer comparer)` | Set the AtomicComparer used to compare atomic values
    `void` | `setResultWhenEmpty​(BooleanValue value)` | Set the result to be returned if one of the operands is an empty sequence
    `java.lang.String` | `tag()` | Get the element name used to identify this expression in exported expression format
    `Expression` | `typeCheck​(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` | Type-check the expression

    - ### Methods inherited from class net.sf.saxon.expr.BinaryExpression

      `computeHashCode, computeSpecialProperties, displayOperator, export, getImplementationMethod, getLhs, getLhsExpression, getOperandRole, getOperator, getRhs, getRhsExpression, isAssociative, isCommutative, isInverse, operands, setFlattened, setLhsExpression, setRhsExpression, toShortString, toString`

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

      `addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, 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, 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

      `getLhs, getLhsExpression, getRhs, getRhsExpression`

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

      `gatherProperties`

- - ### Constructor Detail

    - #### ValueComparison

          public ValueComparison​(Expression p1,
                                 int op,
                                 Expression p2)

      Create a comparison expression identifying the two operands and the operator
      Parameters:
        `p1` - the left-hand operand
        `op` - the operator, as a token returned by the Tokenizer (e.g. Token.LT)
        `p2` - the right-hand operand

  - ### Method Detail

    - #### getExpressionName

          public java.lang.String getExpressionName()

      Get a name identifying the kind of expression, in terms meaningful to a user.
      Overrides:
        `getExpressionName` in class `Expression`
      Returns:
        a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

    - #### setAtomicComparer

          public void setAtomicComparer​(AtomicComparer comparer)

      Set the AtomicComparer used to compare atomic values
      Parameters:
        `comparer` - the AtomicComparer

    - #### getAtomicComparer

          public AtomicComparer getAtomicComparer()

      Get the AtomicComparer used to compare atomic values. This encapsulates any collation that is used. Note that the comparer is always known at compile time.
      Specified by:
        `getAtomicComparer` in interface `ComparisonExpression`

    - #### 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.

    - #### setResultWhenEmpty

          public void setResultWhenEmpty​(BooleanValue value)

      Set the result to be returned if one of the operands is an empty sequence
      Parameters:
        `value` - the result to be returned if an operand is empty. Supply null to mean the empty sequence.

    - #### getResultWhenEmpty

          public BooleanValue getResultWhenEmpty()

      Get the result to be returned if one of the operands is an empty sequence
      Returns:
        BooleanValue.TRUE, BooleanValue.FALSE, or null (meaning the empty sequence)

    - #### 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

    - #### typeCheck

          public Expression typeCheck​(ExpressionVisitor visitor,
                                      ContextItemStaticInfo contextInfo)
                               throws XPathException

      Type-check the expression
      Overrides:
        `typeCheck` in class `BinaryExpression`
      Parameters:
        `visitor` - an expression visitor
        `contextInfo` - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
      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)

    - #### optimize

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

      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.

      Overrides:
        `optimize` in class `BinaryExpression`
      Parameters:
        `visitor` - an 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)

    - #### isNegatable

          public boolean isNegatable​(TypeHierarchy th)

      Check whether this specific instance of the expression is negatable
      Specified by:
        `isNegatable` in interface `Negatable`
      Parameters:
        `th` - the type hierarchy
      Returns:
        true if it is

    - #### negate

          public Expression negate()

      Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false(). The result must be the same as not(this) even in the case where one of the operands is ().
      Specified by:
        `negate` in interface `Negatable`
      Returns:
        the inverted comparison

    - #### equals

          public boolean equals​(java.lang.Object other)

      Description copied from class: `BinaryExpression`
      Is this expression the same as another expression?
      Overrides:
        `equals` in class `BinaryExpression`
      Parameters:
        `other` - the other operand; the result is false if this is not an Expression
      Returns:
        true if the other operand is an expression and if it can be determined that the two expressions are equivalent, in the sense that they will always return the same result.

    - #### copy

          public Expression copy​(RebindingMap rebindings)

      Copy an expression. This makes a deep copy.
      Specified by:
        `copy` in class `Expression`
      Parameters:
        `rebindings` - variables that need to be re-bound
      Returns:
        the copy of the original expression

    - #### effectiveBooleanValue

          public boolean effectiveBooleanValue​(XPathContext context)
                                        throws XPathException

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

    - #### compare

          public static boolean compare​(AtomicValue v0,
                                        int op,
                                        AtomicValue v1,
                                        AtomicComparer comparer,
                                        boolean checkTypes)
                                 throws XPathException

      Compare two atomic values, using a specified operator and collation
      Parameters:
        `v0` - the first operand
        `op` - the operator, as defined by constants such as `Token.FEQ` or `Token.FLT`
        `v1` - the second operand
        `comparer` - used to compare values. If the comparer is context-sensitive then the context must already have been bound using comparer.provideContext().
        `checkTypes` - set to true if it is necessary to check that the types of the arguments are comparable
      Returns:
        the result of the comparison: -1 for LT, 0 for EQ, +1 for GT
      Throws:
        `XPathException` - if the values are not comparable

    - #### evaluateItem

          public BooleanValue 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, or null representing the empty sequence
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### getItemType

          public ItemType getItemType()

      Determine the data type of the expression
      Specified by:
        `getItemType` in class `Expression`
      Returns:
        Type.BOOLEAN

    - #### getStaticUType

          public UType getStaticUType​(UType contextItemType)

      Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
      Overrides:
        `getStaticUType` in class `Expression`
      Parameters:
        `contextItemType` - the static type of the context item
      Returns:
        the static item type of the expression according to the XSLT 3.0 defined rules

    - #### computeCardinality

          public int computeCardinality()

      Determine the static cardinality.
      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`. May also return `StaticProperty.ALLOWS_ZERO` if the result is known to be an empty sequence, or `StaticProperty.ALLOWS_MANY` if if is known to return a sequence of length two or more.

    - #### tag

          public java.lang.String tag()

      Description copied from class: `BinaryExpression`
      Get the element name used to identify this expression in exported expression format
      Overrides:
        `tag` in class `BinaryExpression`
      Returns:
        the element name used to identify this 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