net.sf.saxon.sort
Class EmptyGreatestComparer
java.lang.Object
net.sf.saxon.sort.EmptyGreatestComparer
- AtomicComparer, Serializable
public class EmptyGreatestComparer
extends java.lang.Object
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.
EmptyGreatestComparer
public EmptyGreatestComparer(AtomicComparer baseComparer)
Create an EmptyGreatestComparer
baseComparer
- the comparer used to compare non-empty values (which typically sorts empty
as least)
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.
- compareAtomicValues in interface AtomicComparer
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.
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.
- comparesEqual in interface AtomicComparer
a
- the first object to be compared.b
- the second object to be compared.
- true if the values are equal, false if not
getBaseComparer
public AtomicComparer getBaseComparer()
Get the underlying comparer (which compares empty least)
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.
- getComparisonKey in interface AtomicComparer
provideContext
public AtomicComparer provideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison
- provideContext in interface AtomicComparer
context
- the dynamic evaluation context
- either the original AtomicComparer, or a new AtomicComparer in which the context
is known. The original AtomicComparer is not modified