Package net.sf.saxon.expr

## Class IsLastExpression

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

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

      public final class IsLastExpression
      extends Expression

  A position() eq last() expression, generated by the optimizer.

- - ### 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
    --- | ---
    `IsLastExpression​(boolean condition)` | Construct a condition that tests position() eq last() (if condition is true) or position() ne last() (if condition is false).

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `int` | `computeCardinality()` | Determine the static cardinality
    `int` | `computeHashCode()` | Hashcode supporting equals()
    `int` | `computeSpecialProperties()` | Determine the special properties of this expression
    `Expression` | `copy​(RebindingMap rebindings)` | Copy an expression.
    `boolean` | `equals​(java.lang.Object other)` | Is this expression the same as another expression?
    `BooleanValue` | `evaluateItem​(XPathContext c)` | Evaluate an expression as a single item.
    `void` | `export​(ExpressionPresenter destination)` | Diagnostic print of expression structure.
    `boolean` | `getCondition()` | Get the condition we are testing for
    `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().
    `int` | `getIntrinsicDependencies()` | Get the dependencies of this expression on the context
    `ItemType` | `getItemType()` | Determine the data type of the expression
    `java.lang.String` | `getStreamerName()` | Get the (partial) name of a class that supports streaming of this kind of expression
    `Expression` | `optimize​(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType)` | Perform optimisation of an expression and its subexpressions.
    `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)` | Perform type checking of an expression and its subexpressions.

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

      `addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, toShortString, 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

    - #### IsLastExpression

          public IsLastExpression​(boolean condition)

      Construct a condition that tests position() eq last() (if condition is true) or position() ne last() (if condition is false).
      Parameters:
        `condition` - true if we are testing "equals", false for "not equals".

  - ### Method Detail

    - #### getCondition

          public boolean getCondition()

      Get the condition we are testing for
      Returns:
        true if we are testing "equals", false for "not equals".

    - #### typeCheck

          public Expression typeCheck​(ExpressionVisitor visitor,
                                      ContextItemStaticInfo contextInfo)

      Description copied from class: `Expression`
      Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

      This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

      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

    - #### optimize

          public Expression optimize​(ExpressionVisitor visitor,
                                     ContextItemStaticInfo contextItemType)

      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

    - #### computeSpecialProperties

          public int computeSpecialProperties()

      Determine the special properties of this expression
      Overrides:
        `computeSpecialProperties` in class `Expression`
      Returns:
        `StaticProperty.NO_NODES_NEWLY_CREATED`.

    - #### evaluateItem

          public BooleanValue evaluateItem​(XPathContext c)
                                    throws XPathException

      Description copied from class: `Expression`
      Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
      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

    - #### getItemType

          public ItemType getItemType()

      Determine the data type of the expression
      Specified by:
        `getItemType` in class `Expression`
      Returns:
        Type.BOOLEAN

    - #### 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.

    - #### getIntrinsicDependencies

          public int getIntrinsicDependencies()

      Get the dependencies of this expression on the context
      Overrides:
        `getIntrinsicDependencies` in class `Expression`
      Returns:
        a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

    - #### copy

          public Expression copy​(RebindingMap rebindings)

      Copy an expression. This makes a deep copy.
      Specified by:
        `copy` in class `Expression`
      Parameters:
        `rebindings` -
      Returns:
        the copy of the original expression

    - #### 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`

    - #### equals

          public boolean equals​(java.lang.Object other)

      Is this expression the same as another expression?
      Overrides:
        `equals` in class `Expression`
      Parameters:
        `other` - the expression to be compared with this one
      Returns:
        true if the two expressions are statically equivalent

    - #### computeHashCode

          public int computeHashCode()

      Hashcode supporting equals()
      Overrides:
        `computeHashCode` in class `Expression`
      Returns:
        a computed hash code

    - #### 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.

    - #### 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.

    - #### toString

          public java.lang.String toString()

      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.

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

    - #### getStreamerName

          public java.lang.String getStreamerName()

      Get the (partial) name of a class that supports streaming of this kind of expression
      Overrides:
        `getStreamerName` in class `Expression`
      Returns:
        the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class