## net.sf.saxon.sort
Class SortExpression

    java.lang.Object
      net.sf.saxon.expr.ComputedExpression
          net.sf.saxon.sort.SortExpression

All Implemented Interfaces:
  Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

public class SortExpression
extends ComputedExpression

Expression equivalent to the imaginary syntax expr sortby (sort-key)+

See Also:
  Serialized Form

Field Summary

Fields inherited from class net.sf.saxon.expr.ComputedExpression
`locationId, staticProperties`

Fields inherited from interface net.sf.saxon.expr.Expression
`EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD`

Constructor Summary
`SortExpression(Expression select, SortKeyDefinition[] sortKeys)`

Method Summary
`Expression` `analyze(StaticContext env, ItemType contextItemType)` Type-check the expression
`int` `computeCardinality()` Determine the static cardinality
`int` `computeSpecialProperties()` Get the static properties of this expression (other than its type).
`void` `display(int level, NamePool pool, java.io.PrintStream out)` Diagnostic print of expression structure.
`ItemType` `getItemType()` Determine the data type of the items returned by the expression, if possible
`boolean` `isSortKey(Expression child)` Test whether a given expression is one of the sort keys
`SequenceIterator` `iterate(XPathContext context)` Enumerate the results of the expression
`java.util.Iterator` `iterateSubExpressions()` Get the immediate sub-expressions of this expression.
`Expression` `promote(PromotionOffer offer)` Offer promotion for this subexpression.
`Expression` `simplify(StaticContext env)` Simplify an expression

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

`adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getParentExpression, getPublicId, getSpecialProperties, getSystemId, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, typeError, typeError`

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

Constructor Detail

### SortExpression

    public SortExpression(Expression select,
                          SortKeyDefinition[] sortKeys)

Method Detail

### iterateSubExpressions

    public java.util.Iterator 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.

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

### simplify

    public Expression simplify(StaticContext env)
                        throws XPathException

  Simplify an expression

  Specified by:
    `simplify` in interface `Expression`
  Overrides:
    `simplify` in class `ComputedExpression`
  Returns:
    the simplified expression
  Throws:
    `XPathException` - if an error is discovered during expression rewriting

### analyze

    public Expression analyze(StaticContext env,
                              ItemType contextItemType)
                       throws XPathException

  Type-check the expression

  Parameters:
    `env` - the static context of the expression
    `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`

### promote

    public Expression promote(PromotionOffer offer)
                       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.

  Specified by:
    `promote` in interface `Expression`
  Overrides:
    `promote` in class `ComputedExpression`
  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
  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

### isSortKey

    public boolean isSortKey(Expression child)

  Test whether a given expression is one of the sort keys

### computeCardinality

    public int computeCardinality()

  Determine the static cardinality

  Specified by:
    `computeCardinality` in class `ComputedExpression`

### getItemType

    public ItemType getItemType()

  Determine the data type of the items returned by the expression, if possible

  Returns:
    a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)

### 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 `ComputedExpression`

### iterate

    public SequenceIterator iterate(XPathContext context)
                             throws XPathException

  Enumerate the results of the expression

  Specified by:
    `iterate` in interface `Expression`
  Overrides:
    `iterate` in class `ComputedExpression`
  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

### display

    public void display(int level,
                        NamePool pool,
                        java.io.PrintStream out)

  Description copied from interface: `Expression`
  Diagnostic print of expression structure. The expression is written to the System.err output stream

  Parameters:
    `level` - indentation level for this expression
    `pool` - NamePool used to expand any names appearing in the expression
    `out` - Output destination