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## net.sf.saxon.expr
Class ValueComparison

    java.lang.Object
      net.sf.saxon.expr.ComputedExpression
          net.sf.saxon.expr.BinaryExpression
              net.sf.saxon.expr.ValueComparison

All Implemented Interfaces:
  Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

public final class ValueComparison
extends BinaryExpression

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

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.ComputedExpression
`locationId, staticProperties`

Fields inherited from interface net.sf.saxon.expr.Expression
`EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD`

Constructor Summary
`ValueComparison(Expression p1, int op, Expression p2)` Create a relational expression identifying the two operands and the operator

Method Summary
`boolean` | `effectiveBooleanValue(XPathContext context)` Evaluate the expression in a boolean context
`Item` | `evaluateItem(XPathContext context)` Evaluate the expression in a given context
`ItemType` | `getItemType(TypeHierarchy th)` Determine the data type of the expression
`ValueComparison` | `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(Optimizer opt, StaticContext env, ItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
`Expression` | `typeCheck(StaticContext env, ItemType contextItemType)` Type-check the expression

Methods inherited from class net.sf.saxon.expr.BinaryExpression
`computeCardinality, computeSpecialProperties, display, displayOperator, equals, getOperands, getOperator, hashCode, isCommutative, isInverse, iterateSubExpressions, promote, simplify`

Methods inherited from class net.sf.saxon.expr.ComputedExpression
`adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError`

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

Constructor Detail

### ValueComparison

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

  Create a relational 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

### typeCheck

    public Expression typeCheck(StaticContext env,
                                ItemType contextItemType)
                         throws XPathException

  Type-check the expression

  Specified by:
    `typeCheck` in interface `Expression`
  Overrides:
    `typeCheck` in class `BinaryExpression`
  Throws:
    `XPathException`

### optimize

    public Expression optimize(Optimizer opt,
                               StaticContext env,
                               ItemType contextItemType)
                        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.

  Specified by:
    `optimize` in interface `Expression`
  Overrides:
    `optimize` in class `BinaryExpression`
  Parameters:
    `opt` - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.
    `env` - the static context of the expression
    `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 if appropriate to optimize execution
  Throws:
    `StaticError` - if an error is discovered during this phase (typically a type error)
    `XPathException`

### negate

    public ValueComparison negate()

  Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false()

### effectiveBooleanValue

    public boolean effectiveBooleanValue(XPathContext context)
                                  throws XPathException

  Evaluate the expression in a boolean context

  Specified by:
    `effectiveBooleanValue` in interface `Expression`
  Overrides:
    `effectiveBooleanValue` in class `ComputedExpression`
  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

### evaluateItem

    public Item evaluateItem(XPathContext context)
                      throws XPathException

  Evaluate the expression in a given context

  Specified by:
    `evaluateItem` in interface `Expression`
  Overrides:
    `evaluateItem` in class `ComputedExpression`
  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(TypeHierarchy th)

  Determine the data type of the expression

  Parameters:
    `th` -
  Returns:
    Type.BOOLEAN

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