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## net.sf.saxon.expr.instruct
Class SimpleContentConstructor

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.expr.instruct.SimpleContentConstructor

All Implemented Interfaces:
  Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator

    public class SimpleContentConstructor

extends Expression

This class implements the rules for an XSLT (or XQuery) simple content constructor, which are used in constructing the string value of an attribute node, text node, comment node, etc, from the value of the select expression or the contained sequence constructor.

See Also:
  Serialized Form

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression
`EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD`

Constructor Summary
`SimpleContentConstructor(Expression select, Expression separator)` Create a SimpleContentConstructor

Method Summary
`PathMap.PathMapNodeSet` | `addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)` Add a representation of this expression to a PathMap.
`protected int` | `computeCardinality()` Compute the cardinality of the result of the expression.
`Expression` | `copy()` Copy an expression.
`Item` | `evaluateItem(XPathContext context)` Evaluate an expression as a single item.
`void` | `explain(ExpressionPresenter out)` Diagnostic print of expression structure.
`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(TypeHierarchy th)` Determine the data type of the expression, if possible.
`Expression` | `getSelectExpression()` Get the select expression
`Expression` | `getSeparatorExpression()` Get the separator expression
`boolean` | `isAtomic()` Determine if the select expression is atomic
`boolean` | `isSingleton()` Determine whether the select expression is a singleton (an expression returning zero or one items)
`Iterator<Expression>` | `iterateSubExpressions()` Get the immediate sub-expressions of this expression.
`Expression` | `optimize(ExpressionVisitor visitor, ItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
`void` | `process(XPathContext context, int locationId, int options)` Process the instruction, without returning any tail calls
`Expression` | `promote(PromotionOffer offer, Expression parent)` Offer promotion for this subexpression.
`boolean` | `replaceSubExpression(Expression original, Expression replacement)` Replace one subexpression by a replacement subexpression
`Expression` | `simplify(ExpressionVisitor visitor)` Simplify an expression.
`Expression` | `typeCheck(ExpressionVisitor visitor, ItemType contextItemType)` Perform type checking of an expression and its subexpressions.

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

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

Constructor Detail

### SimpleContentConstructor

    public SimpleContentConstructor(Expression select,
                                    Expression separator)

  Create a SimpleContentConstructor

  Parameters:
    `select` - the select expression (which computes a sequence of strings)
    `separator` - the separator expression (which computes a value to separate adjacent strings)

Method Detail

### getSelectExpression

    public Expression getSelectExpression()

  Get the select expression

  Returns:
    the select expression

### getSeparatorExpression

    public Expression getSeparatorExpression()

  Get the separator expression

  Returns:
    the separator expression

### isSingleton

    public boolean isSingleton()

  Determine whether the select expression is a singleton (an expression returning zero or one items)

  Returns:
    true if the select expression will always be of length zero or one

### isAtomic

    public boolean isAtomic()

  Determine if the select expression is atomic

  Returns:
    true if the select expression always returns atomic values

### computeCardinality

    protected int computeCardinality()

  Compute the cardinality of the result of the expression.

  Specified by:
    `computeCardinality` in class `Expression`
  Returns:
    the cardinality, @link {StaticProperty.EXACTLY_ONE}

### copy

    public Expression copy()

  Copy an expression. This makes a deep copy.

  Specified by:
    `copy` in class `Expression`
  Returns:
    the copy of the original expression

### simplify

    public Expression simplify(ExpressionVisitor visitor)
                        throws XPathException

  Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

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

### typeCheck

    public Expression typeCheck(ExpressionVisitor visitor,
                                ItemType contextItemType)
                         throws XPathException

  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.

  If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

  Overrides:
    `typeCheck` 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 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,
                               ItemType 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)

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

  This method should always return a result, though it may be the best approximation that is available at the time.

  Specified by:
    `getItemType` in class `Expression`
  Parameters:
    `th` - the type hierarchy cache
  Returns:
    a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

### explain

    public void explain(ExpressionPresenter out)

  Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

  Specified by:
    `explain` in class `Expression`
  Parameters:
    `out` - the expression presenter used to display the structure

### iterateSubExpressions

    public Iterator<Expression> iterateSubExpressions()

  Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

  Overrides:
    `iterateSubExpressions` in class `Expression`
  Returns:
    an iterator containing the sub-expressions of this expression

### replaceSubExpression

    public boolean replaceSubExpression(Expression original,
                                        Expression replacement)

  Replace one subexpression by a replacement subexpression

  Overrides:
    `replaceSubExpression` in class `Expression`
  Parameters:
    `original` - the original subexpression
    `replacement` - the replacement subexpression
  Returns:
    true if the original subexpression is found

### promote

    public Expression promote(PromotionOffer offer,
                              Expression parent)
                       throws XPathException

  Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

  Overrides:
    `promote` in class `Expression`
  Parameters:
    `offer` - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
    `parent` -
  Returns:
    if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
  Throws:
    `XPathException` - if any error is detected

### addToPathMap

    public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                               PathMap.PathMapNodeSet pathMapNodeSet)

  Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

  The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

  Overrides:
    `addToPathMap` in class `Expression`
  Parameters:
    `pathMap` - the PathMap to which the expression should be added
    `pathMapNodeSet` - the PathMapNodeSet to which the paths embodied in this expression should be added
  Returns:
    the pathMapNodeSet representing the points in the source document that are both reachable by this expression, and that represent possible results of this expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

### evaluateItem

    public Item evaluateItem(XPathContext context)
                      throws XPathException

  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.

  Specified by:
    `evaluateItem` in interface `EvaluableItem`
  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

### process

    public void process(XPathContext context,
                        int locationId,
                        int options)
                 throws XPathException

  Process the instruction, without returning any tail calls

  Parameters:
    `context` - The dynamic context, giving access to the current node, the current variables, etc.
  Throws:
    `XPathException`

### 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 prefered.

  Overrides:
    `getImplementationMethod` in class `Expression`
  Returns:
    the implementation method, for example `Expression.ITERATE_METHOD` or `Expression.EVALUATE_METHOD` or `Expression.PROCESS_METHOD`

### getExpressionName

    public 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 explain() output displaying the expression.

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Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.