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:

java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, Negatable, SequenceIterable, InstructionInfo, org.xml.sax.Locator
```
public class Existence
extends SystemFunction
implements Negatable
```
Implement the exists() and empty() functions

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type Field Description

static int EMPTY

static int EXISTS
- Fields inherited from class net.sf.saxon.expr.Expression
  EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
- Fields inherited from class net.sf.saxon.expr.FunctionCall
  argument
- Fields inherited from class net.sf.saxon.functions.SystemFunction
  operation

Fields
Modifier and Type	Field	Description
`static int`	`EMPTY`
`static int`	`EXISTS`

Constructor Summary

Constructors
Constructor Description

Existence()

Constructors
Constructor	Description
`Existence()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`checkArguments(ExpressionVisitor visitor)`	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
`boolean`	`isNegatable(ExpressionVisitor visitor)`	Check whether this specific instance of the expression is negatable
`Expression`	`negate()`	Return the negation of the expression
`Expression`	`optimize(ExpressionVisitor visitor, ItemType contextItemType)`	Perform optimisation of an expression and its subexpressions.

Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, dynamicError, evaluateAsString, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterate, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class net.sf.saxon.expr.FunctionCall
addExternalFunctionCallToPathMap, checkArgumentCount, equals, explain, getArguments, getDisplayName, getFunctionName, getNumberOfArguments, hashCode, iterateSubExpressions, preEvaluate, promote, replaceSubExpression, setArguments, setFunctionName, simplify, simplifyArguments, toString, typeCheck

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

Methods inherited from class net.sf.saxon.functions.SystemFunction
addContextDocumentArgument, addDocToPathMap, computeCardinality, computeSpecialProperties, copy, getDetails, getErrorCodeForTypeErrors, getItemType, getRequiredType, makeSystemFunction, setDetails, useContextItemAsDefault

- 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(ExpressionVisitor visitor)
                    throws XPathException
```
    Static analysis: prevent sorting of the argument
    
    Overrides:
    
    checkArguments in class SystemFunction
    
    Parameters:
    
    visitor - the expression visitor
    
    Throws:
    
    XPathException
  - optimize
```
public Expression optimize(ExpressionVisitor visitor,
                           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.
    
    Overrides:
    
    optimize in class SystemFunction
    
    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 if appropriate to optimize execution
    
    Throws:
    
    XPathException - if an error is discovered during this phase (typically a type error)
  - isNegatable
```
public boolean isNegatable(ExpressionVisitor visitor)
```
    Check whether this specific instance of the expression is negatable
    
    Specified by:
    
    isNegatable in interface Negatable
    
    Returns:
    
    true if it is
  - negate
```
public Expression negate()
```
    Return the negation of the expression
    
    Specified by:
    
    negate in interface Negatable
    
    Returns:
    
    the negation of the expression
  - 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

Class Existence

Field Summary

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

Fields inherited from class net.sf.saxon.expr.FunctionCall

Fields inherited from class net.sf.saxon.functions.SystemFunction

Constructor Summary

Method Summary

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

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

Methods inherited from class java.lang.Object

Methods inherited from class net.sf.saxon.functions.SystemFunction

Field Detail

EXISTS

EMPTY

Constructor Detail

Existence

Method Detail

checkArguments

optimize

isNegatable

negate

effectiveBooleanValue

evaluateItem