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## net.sf.saxon.expr
Class FilterExpression

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.expr.FilterExpression

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

    public final class FilterExpression

extends Expression
implements ContextSwitchingExpression

A FilterExpression contains a base expression and a filter predicate, which may be an integer expression (positional filter), or a boolean expression (qualifier)

See Also:
  Serialized Form

Field Summary
`static int` | `FILTERED`

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
`FilterExpression(Expression start, Expression filter)` Constructor

Method Summary
`PathMap.PathMapNodeSet` | `addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)` Add a representation of this expression to a PathMap.
`int` | `computeCardinality()` Get the static cardinality of this expression
`int` | `computeDependencies()` Determine which aspects of the context the expression depends on.
`int` | `computeSpecialProperties()` Get the static properties of this expression (other than its type).
`Expression` | `copy()` Copy an expression.
`boolean` | `equals(Object other)` Is this expression the same as another expression?
`void` | `explain(ExpressionPresenter out)` Diagnostic print of expression structure.
`Expression` | `getControlledExpression()` Get the subexpression that is evaluated in the new context
`Expression` | `getControllingExpression()` Get the underlying expression
`String` | `getExpressionName()` Get a name identifying the kind of expression, in terms meaningful to a user.
`Expression` | `getFilter()` Get the filter expression
`ItemType` | `getItemType(TypeHierarchy th)` Get the data type of the items returned
`int` | `hashCode()` get HashCode for comparing two expressions
`boolean` | `hasLoopingSubexpression(Expression child)` Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
`boolean` | `isIndependentNumericFilter()` Determine whether the filter is a simple independent numeric, that is, an expression that satisfies the following conditions: (a) its value is numeric; (b) the value does not depend on the context item or position; (c) the cardinality is zero or one.
`boolean` | `isPositional(TypeHierarchy th)` Determine if the filter is positional
`boolean` | `isSimpleBooleanFilter()` Test if the filter always returns a singleton boolean
`SequenceIterator` | `iterate(XPathContext context)` Iterate over the results, returning them in the correct order
`Iterator<Expression>` | `iterateSameFocusSubExpressions()` Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
`Iterator<Expression>` | `iterateSubExpressions()` Get the immediate subexpressions of this expression
`Expression` | `optimize(ExpressionVisitor visitor, ItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
`Expression` | `promote(PromotionOffer offer, Expression parent)` Promote this expression if possible
`boolean` | `replaceSubExpression(Expression original, Expression replacement)` Replace one subexpression by a replacement subexpression
`Expression` | `simplify(ExpressionVisitor visitor)` Simplify an expression
`String` | `toString()` The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
`Expression` | `typeCheck(ExpressionVisitor visitor, ItemType contextItemType)` Type-check the expression

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

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

Field Detail

### FILTERED

    public static final int FILTERED

See Also:
  Constant Field Values

Constructor Detail

### FilterExpression

    public FilterExpression(Expression start,
                            Expression filter)

  Constructor

  Parameters:
    `start` - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.
    `filter` - An expression defining the filter predicate

Method Detail

### 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.

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Get the data type of the items returned

  Specified by:
    `getItemType` in class `Expression`
  Parameters:
    `th` - the type hierarchy cache
  Returns:
    an integer representing the data type

### getControllingExpression

    public Expression getControllingExpression()

  Get the underlying expression

  Specified by:
    `getControllingExpression` in interface `ContextSwitchingExpression`
  Returns:
    the expression being filtered

### getControlledExpression

    public Expression getControlledExpression()

  Get the subexpression that is evaluated in the new context

  Specified by:
    `getControlledExpression` in interface `ContextSwitchingExpression`
  Returns:
    the subexpression evaluated in the context set by the controlling expression

### getFilter

    public Expression getFilter()

  Get the filter expression

  Returns:
    the expression acting as the filter predicate

### isPositional

    public boolean isPositional(TypeHierarchy th)

  Determine if the filter is positional

  Parameters:
    `th` - the Type Hierarchy (for cached access to type information)
  Returns:
    true if the value of the filter depends on the position of the item against which it is evaluated

### isSimpleBooleanFilter

    public boolean isSimpleBooleanFilter()

  Test if the filter always returns a singleton boolean

  Returns:
    true if the filter is a simple boolean expression

### isIndependentNumericFilter

    public boolean isIndependentNumericFilter()

  Determine whether the filter is a simple independent numeric, that is, an expression that satisfies the following conditions: (a) its value is numeric; (b) the value does not depend on the context item or position; (c) the cardinality is zero or one.

  Returns:
    true if the filter is a numeric value that does not depend on the context item or position

### simplify

    public Expression simplify(ExpressionVisitor visitor)
                        throws XPathException

  Simplify an expression

  Overrides:
    `simplify` in class `Expression`
  Parameters:
    `visitor` - the expression visitor
  Returns:
    the simplified expression
  Throws:
    `XPathException` - if any failure occurs

### typeCheck

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

  Type-check the expression

  Overrides:
    `typeCheck` in class `Expression`
  Parameters:
    `visitor` - the expression visitor
    `contextItemType` - the type of the context item for this expression
  Returns:
    the expression after type-checking (potentially modified to add run-time checks and/or conversions)
  Throws:
    `XPathException` - if an error is discovered during this phase (typically a type error)

### 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 `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)

### 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.

  Overrides:
    `addToPathMap` in class `Expression`
  Parameters:
    `pathMap` - the PathMap to which the expression should be added
    `pathMapNodeSet` -
  Returns:
    the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

### promote

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

  Promote this expression if possible

  Overrides:
    `promote` in class `Expression`
  Parameters:
    `offer` - details of the promotion that is possible
    `parent` -
  Returns:
    the promoted expression (or the original expression, unchanged)
  Throws:
    `XPathException` - if any error is detected

### iterateSubExpressions

    public Iterator<Expression> iterateSubExpressions()

  Get the immediate subexpressions of this expression

  Overrides:
    `iterateSubExpressions` in class `Expression`
  Returns:
    the subexpressions, as an array

### iterateSameFocusSubExpressions

    public Iterator<Expression> iterateSameFocusSubExpressions()

  Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.

  Overrides:
    `iterateSameFocusSubExpressions` in class `Expression`
  Returns:
    an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression

### hasLoopingSubexpression

    public boolean hasLoopingSubexpression(Expression child)

  Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly

  Overrides:
    `hasLoopingSubexpression` in class `Expression`
  Parameters:
    `child` - the immediate subexpression
  Returns:
    true if the child expression is evaluated repeatedly

### 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

### computeCardinality

    public int computeCardinality()

  Get the static cardinality of this expression

  Specified by:
    `computeCardinality` in class `Expression`
  Returns:
    the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered

### computeSpecialProperties

    public int computeSpecialProperties()

  Get the static properties of this expression (other than its type). The result is bit-significant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

  Overrides:
    `computeSpecialProperties` in class `Expression`
  Returns:
    the static properties of the expression, as a bit-significant value

### equals

    public boolean equals(Object other)

  Is this expression the same as another expression?

  Overrides:
    `equals` in class `Object`
  Parameters:
    `other` - the expression to be compared with this one
  Returns:
    true if the two expressions are statically equivalent

### hashCode

    public int hashCode()

  get HashCode for comparing two expressions

  Overrides:
    `hashCode` in class `Object`
  Returns:
    the hash code

### iterate

    public SequenceIterator iterate(XPathContext context)
                             throws XPathException

  Iterate over the results, returning them in the correct order

  Specified by:
    `iterate` in interface `SequenceIterable`
  Overrides:
    `iterate` in class `Expression`
  Parameters:
    `context` - the dynamic context for the evaluation
  Returns:
    an iterator over the expression results
  Throws:
    `XPathException` - if any dynamic error occurs

### computeDependencies

    public int computeDependencies()

  Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE

  Overrides:
    `computeDependencies` in class `Expression`
  Returns:
    the dependencies

### 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

### toString

    public String toString()

  The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

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

### 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 ExpressionPresenter to be used

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