## net.sf.saxon.functions
Class Existence

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.expr.FunctionCall
              net.sf.saxon.functions.SystemFunction
                  net.sf.saxon.functions.Existence

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

    public class Existence

extends SystemFunction

Implement the exists() and empty() functions

See Also:
  Serialized Form

Field Summary
`static int` `EMPTY`
`static int` `EXISTS`

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

Constructor Summary
`Existence()`

Method Summary
`void` `checkArguments(StaticContext env)` Static analysis: prevent sorting of the argument
`boolean` `effectiveBooleanValue(XPathContext c)` Evaluate the function in a boolean context
`Item` `evaluateItem(XPathContext c)` Evaluate in a general context

Methods inherited from class net.sf.saxon.functions.SystemFunction
`computeCardinality, computeSpecialProperties, display, getDetails, getErrorCodeForTypeErrors, getItemType, main, makeSystemFunction, optimize, setDetails`

Methods inherited from class net.sf.saxon.expr.FunctionCall
`getArguments, getDisplayName, getFunctionNameCode, getNumberOfArguments, iterateSubExpressions, preEvaluate, promote, replaceSubExpression, setArguments, setFunctionNameCode, simplify, typeCheck`

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

`adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, evaluateAsString, getCardinality, getColumnNumber, getContainingProcedure, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation`

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

Field Detail

### EXISTS

    public static final int EXISTS

See Also:
  Constant Field Values

### EMPTY

    public static final int EMPTY

See Also:
  Constant Field Values

Constructor Detail

### Existence

    public Existence()

Method Detail

### checkArguments

    public void checkArguments(StaticContext env)
                        throws XPathException

  Static analysis: prevent sorting of the argument

  Overrides:
    `checkArguments` in class `SystemFunction`
  Throws:
    `XPathException`

### effectiveBooleanValue

    public boolean effectiveBooleanValue(XPathContext c)
                                  throws XPathException

  Evaluate the function in a boolean context

  Overrides:
    `effectiveBooleanValue` in class `Expression`
  Parameters:
    `c` - 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

### evaluateItem

    public Item evaluateItem(XPathContext c)
                      throws XPathException

  Evaluate in a general context

  Specified by:
    `evaluateItem` in interface `EvaluableItem`
  Overrides:
    `evaluateItem` in class `Expression`
  Parameters:
    `c` - The context in which the expression is to be evaluated
  Returns:
    the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

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