net.sf.saxon.expr.sort
Class EmptyGreatestComparer

java.lang.Object
  net.sf.saxon.expr.sort.EmptyGreatestComparer

All Implemented Interfaces:

Serializable, AtomicComparer

public class EmptyGreatestComparer
extends Object
implements AtomicComparer, Serializable

A Comparer that modifies a base comparer by sorting empty key values and NaN values last (greatest), as opposed to the default which sorts them first.

Author:

Michael H. Kay

See Also:

Serialized Form

Constructor Summary

EmptyGreatestComparer(AtomicComparer baseComparer)
Create an EmptyGreatestComparer

Method Summary

int	compareAtomicValues(AtomicValue a, AtomicValue b) Compare two AtomicValue objects according to the rules for their data type.
boolean	comparesEqual(AtomicValue a, AtomicValue b) Compare two AtomicValue objects for equality according to the rules for their data type.
AtomicComparer	getBaseComparer() Get the underlying comparer (which compares empty least)
StringCollator	getCollator() Get the collation used by this AtomicComparer if any
ComparisonKey	getComparisonKey(AtomicValue a) Get a comparison key for an object.
AtomicComparer	provideContext(XPathContext context) Supply the dynamic context in case this is needed for the comparison

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

EmptyGreatestComparer

public EmptyGreatestComparer(AtomicComparer baseComparer)

Create an EmptyGreatestComparer

Parameters:

baseComparer - the comparer used to compare non-empty values (which typically sorts empty as least)

Method Detail

getBaseComparer

public AtomicComparer getBaseComparer()

Get the underlying comparer (which compares empty least)

Returns:

the base comparer

getCollator

public StringCollator getCollator()

Description copied from interface: AtomicComparer

Get the collation used by this AtomicComparer if any

Specified by:

getCollator in interface AtomicComparer

Returns:

the collation used for comparing strings, or null if not applicable

provideContext

public AtomicComparer provideContext(XPathContext context)

Supply the dynamic context in case this is needed for the comparison

Specified by:

provideContext in interface AtomicComparer

Parameters:

context - the dynamic evaluation context

Returns:

either the original AtomicComparer, or a new AtomicComparer in which the context is known. The original AtomicComparer is not modified

compareAtomicValues

public int compareAtomicValues(AtomicValue a,
                               AtomicValue b)
                        throws NoDynamicContextException

Compare two AtomicValue objects according to the rules for their data type. UntypedAtomic values are compared as if they were strings; if different semantics are wanted, the conversion must be done by the caller.

Specified by:

compareAtomicValues in interface AtomicComparer

Parameters:

a - the first object to be compared. It is intended that this should normally be an instance of AtomicValue, though this restriction is not enforced. If it is a StringValue, the collator is used to compare the values, otherwise the value must implement the java.util.Comparable interface.

b - the second object to be compared. This must be comparable with the first object: for example, if one is a string, they must both be strings.

Returns:

<0 if a0 if a>b

Throws:

ClassCastException - if the objects are not comparable

NoDynamicContextException - if this comparer required access to dynamic context information, notably the implicit timezone, and this information is not available. In general this happens if a context-dependent comparison is attempted at compile-time, and it signals the compiler to generate code that tries again at run-time.

comparesEqual

public boolean comparesEqual(AtomicValue a,
                             AtomicValue b)
                      throws NoDynamicContextException

Compare two AtomicValue objects for equality according to the rules for their data type. UntypedAtomic values are compared by converting to the type of the other operand.

Specified by:

comparesEqual in interface AtomicComparer

Parameters:

a - the first object to be compared.

b - the second object to be compared.

Returns:

true if the values are equal, false if not

Throws:

ClassCastException - if the objects are not comparable

NoDynamicContextException

getComparisonKey

public ComparisonKey getComparisonKey(AtomicValue a)
                               throws NoDynamicContextException

Get a comparison key for an object. This must satisfy the rule that if two objects are equal according to the XPath eq operator, then their comparison keys are equal according to the Java equals() method, and vice versa. There is no requirement that the comparison keys should reflect the ordering of the underlying objects.

Specified by:

getComparisonKey in interface AtomicComparer

Throws:

NoDynamicContextException