net.sf.saxon.sort

Class EmptyGreatestComparer

Implemented Interfaces:
AtomicComparer, Serializable

public class EmptyGreatestComparer
extends java.lang.Object
implements AtomicComparer, java.io.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)
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

Constructor Details

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 Details

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

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

getBaseComparer

public AtomicComparer getBaseComparer()
Get the underlying comparer (which compares empty least)
Returns:
the base comparer

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

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