Package net.sf.saxon.expr

## Class ErrorExpression

- java.lang.Object
- - net.sf.saxon.expr.Expression
  - - net.sf.saxon.expr.ErrorExpression

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

      public class ErrorExpression
      extends Expression

  Error expression: this expression is generated when the supplied expression cannot be parsed, and the containing element enables forwards-compatible processing. It defers the generation of an error message until an attempt is made to evaluate the expression

- - ### Field Summary

    - ### 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
    --- | ---
    `ErrorExpression()` | This constructor is never executed, but it is used in the expression parser as a dummy so that the Java compiler recognizes parsing methods as always returning a non-null result.
    `ErrorExpression​(java.lang.String message, java.lang.String errorCode, boolean isTypeError)` | Create an ErrorExpression, which if evaluated, generates a dynamic error
    `ErrorExpression​(XmlProcessingError exception)` | Constructor taking an exception.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `int` | `computeCardinality()` | Determine the static cardinality
    `Expression` | `copy​(RebindingMap rebindings)` | Copy an expression.
    `Item` | `evaluateItem​(XPathContext context)` | Evaluate the expression.
    `void` | `export​(ExpressionPresenter destination)` | Diagnostic print of expression structure.
    `java.lang.String` | `getErrorCodeLocalPart()` |
    `XmlProcessingError` | `getException()` | Get the wrapped exception
    `java.lang.String` | `getExpressionName()` | Get a name identifying the kind of expression, in terms meaningful to a user.
    `int` | `getImplementationMethod()` | An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
    `ItemType` | `getItemType()` | Determine the data type of the expression, if possible
    `java.lang.String` | `getMessage()` |
    `boolean` | `isTypeError()` |
    `SequenceIterator` | `iterate​(XPathContext context)` | Iterate over the expression.
    `Expression` | `optimize​(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType)` | Perform optimisation of an expression and its subexpressions.
    `void` | `setOriginalExpression​(Expression original)` | Set the original expression (for diagnostics)
    `java.lang.String` | `toShortString()` | Produce a short string identifying the expression for use in error messages
    `java.lang.String` | `toString()` | The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.
    `Expression` | `typeCheck​(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` | Type-check the expression.

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

      `addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeHashCode, computeSpecialProperties, computeStaticProperties, dynamicError, effectiveBooleanValue, equals, 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, getStaticUType, getStreamerName, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, 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.trace.Traceable

      `gatherProperties`

- - ### Constructor Detail

    - #### ErrorExpression

          public ErrorExpression()

      This constructor is never executed, but it is used in the expression parser as a dummy so that the Java compiler recognizes parsing methods as always returning a non-null result.

    - #### ErrorExpression

          public ErrorExpression​(java.lang.String message,
                                 java.lang.String errorCode,
                                 boolean isTypeError)

      Create an ErrorExpression, which if evaluated, generates a dynamic error
      Parameters:
        `message` - the error message
        `errorCode` - the error code
        `isTypeError` - true if this is a type error

    - #### ErrorExpression

          public ErrorExpression​(XmlProcessingError exception)

      Constructor taking an exception. Creating exceptions is expensive, so this constructor should be used only if the exception object already exists.
      Parameters:
        `exception` - the error to be thrown when this expression is evaluated

  - ### Method Detail

    - #### getException

          public XmlProcessingError getException()

      Get the wrapped exception
      Returns:
        the exception to be thrown when the expression is evaluated

    - #### isTypeError

          public boolean isTypeError()

    - #### getMessage

          public java.lang.String getMessage()

    - #### getErrorCodeLocalPart

          public java.lang.String getErrorCodeLocalPart()

    - #### setOriginalExpression

          public void setOriginalExpression​(Expression original)

      Set the original expression (for diagnostics)
      Parameters:
        `original` - the expression that this error expression replaces

    - #### typeCheck

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

      Type-check the expression.
      Overrides:
        `typeCheck` in class `Expression`
      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 contextItemType)
                              throws XPathException

      Description copied from class: `Expression`
      Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

      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 `Expression`
      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)

    - #### getImplementationMethod

          public int getImplementationMethod()

      An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.
      Specified by:
        `getImplementationMethod` in class `Expression`
      Returns:
        the implementation method, for example `Expression.ITERATE_METHOD` or `Expression.EVALUATE_METHOD` or `Expression.PROCESS_METHOD`

    - #### evaluateItem

          public Item evaluateItem​(XPathContext context)
                            throws XPathException

      Evaluate the expression. This always throws the exception registered when the expression was first parsed.
      Overrides:
        `evaluateItem` in class `Expression`
      Parameters:
        `context` - 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

    - #### iterate

          public SequenceIterator iterate​(XPathContext context)
                                   throws XPathException

      Iterate over the expression. This always throws the exception registered when the expression was first parsed.
      Overrides:
        `iterate` in class `Expression`
      Parameters:
        `context` - supplies the context for evaluation
      Returns:
        a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### getItemType

          public ItemType getItemType()

      Determine the data type of the expression, if possible
      Specified by:
        `getItemType` in class `Expression`
      Returns:
        Type.ITEM (meaning not known in advance)

    - #### computeCardinality

          public int computeCardinality()

      Determine the static cardinality
      Specified by:
        `computeCardinality` in class `Expression`
      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.

    - #### copy

          public Expression copy​(RebindingMap rebindings)

      Description copied from class: `Expression`
      Copy an expression. This makes a deep copy.
      Specified by:
        `copy` in class `Expression`
      Parameters:
        `rebindings` - a mutable list of (old binding, new binding) pairs that is used to update the bindings held in any local variable references that are copied.
      Returns:
        the copy of the original expression

    - #### 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 export() output displaying the expression.

    - #### toString

          public java.lang.String toString()

      Description copied from class: `Expression`

      The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.

      For subclasses of Expression that represent XPath expressions, the result should always be a string that parses as an XPath 3.0 expression. The expression produced should be equivalent to the original making certain assumptions about the static context. In general the expansion will make no assumptions about namespace bindings, except that (a) the prefix "xs" is used to refer to the XML Schema namespace, and (b) the default function namespace is assumed to be the "fn" namespace.

      In the case of XSLT instructions and XQuery expressions, the toString() method gives an abstracted view of the syntax that is not designed in general to be parseable.

      Overrides:
        `toString` in class `Expression`
      Returns:
        a representation of the expression as a string

    - #### toShortString

          public java.lang.String toShortString()

      Description copied from class: `Expression`
      Produce a short string identifying the expression for use in error messages
      Overrides:
        `toShortString` in class `Expression`
      Returns:
        a short string, sufficient to identify the expression

    - #### export

          public void export​(ExpressionPresenter destination)
                      throws XPathException

      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
        `export` in interface `ExportAgent`
      Specified by:
        `export` in class `Expression`
      Parameters:
        `destination` - the expression presenter used to display the structure
      Throws:
        `XPathException` - if the export fails, for example if an expression is found that won't work in the target environment.