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## net.sf.saxon.expr
Class VennExpression

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

All Implemented Interfaces:
  Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, InstructionInfoProvider

    public class VennExpression

extends BinaryExpression

An expression representing a nodeset that is a union, difference, or intersection of two other NodeSets

See Also:
  Serialized Form

Field Summary

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

Constructor Summary
`VennExpression(Expression p1, int op, Expression p2)` Constructor

Method Summary
`int` | `computeCardinality()` Determine the static cardinality of the expression
`int` | `computeSpecialProperties()` Get the static properties of this expression (other than its type).
`boolean` | `effectiveBooleanValue(XPathContext context)` Get the effective boolean value.
`ItemType` | `getItemType(TypeHierarchy th)` Determine the data type of the items returned by this expression
`int` | `hashCode()` Is this expression the same as another expression?
`SequenceIterator` | `iterate(XPathContext c)` Iterate over the value of the expression.
`Expression` | `simplify(StaticContext env)` Simplify the expression
`Expression` | `typeCheck(StaticContext env, ItemType contextItemType)` Type-check the expression

Methods inherited from class net.sf.saxon.expr.BinaryExpression
`display, equals, getOperands, getOperator, iterateSubExpressions, optimize, promote, replaceSubExpression`

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

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

Constructor Detail

### VennExpression

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

  Constructor

  Parameters:
    `p1` - the left-hand operand
    `op` - the operator (union, intersection, or difference)
    `p2` - the right-hand operand

Method Detail

### getItemType

    public final ItemType getItemType(TypeHierarchy th)

  Determine the data type of the items returned by this expression

  Specified by:
    `getItemType` in class `Expression`
  Parameters:
    `th` -
  Returns:
    the data type

### computeCardinality

    public final int computeCardinality()

  Determine the static cardinality of the expression

  Overrides:
    `computeCardinality` in class `BinaryExpression`

### computeSpecialProperties

    public int computeSpecialProperties()

  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 `BinaryExpression`
  Returns:
    `StaticProperty.NON_CREATIVE`. This is overridden for some subclasses.

### simplify

    public Expression simplify(StaticContext env)
                        throws XPathException

  Simplify the expression

  Overrides:
    `simplify` in class `BinaryExpression`
  Returns:
    the simplified expression
  Throws:
    `XPathException` - if an error is discovered during expression rewriting

### typeCheck

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

  Type-check the expression

  Overrides:
    `typeCheck` in class `BinaryExpression`
  Parameters:
    `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 to perform necessary run-time type checks, and to perform other type-related optimizations
  Throws:
    `StaticError` - if an error is discovered during this phase (typically a type error)
    `XPathException`

### hashCode

    public int hashCode()

  Is this expression the same as another expression?

  Overrides:
    `hashCode` in class `BinaryExpression`

### iterate

    public SequenceIterator iterate(XPathContext c)
                             throws XPathException

  Iterate over the value of the expression. The result will always be sorted in document order, with duplicates eliminated

  Specified by:
    `iterate` in interface `SequenceIterable`
  Overrides:
    `iterate` in class `Expression`
  Parameters:
    `c` - The context for evaluation
  Returns:
    a SequenceIterator representing the union of the two operands
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

### effectiveBooleanValue

    public boolean effectiveBooleanValue(XPathContext context)
                                  throws XPathException

  Get the effective boolean value. In the case of a union expression, this is reduced to an OR expression, for efficiency

  Overrides:
    `effectiveBooleanValue` in class `Expression`
  Parameters:
    `context` - The context in which the expression is to be evaluated
  Returns:
    the effective boolean value
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

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Copyright (C) Michael H. Kay. All rights reserved.