net.sf.saxon.sort
Class NumericComparer

java.lang.Object
  net.sf.saxon.sort.NumericComparer

All Implemented Interfaces:

Serializable, AtomicComparer

public class NumericComparer
extends Object
implements AtomicComparer, Serializable

A Comparer used for comparing sort keys when data-type="number". The items to be compared are converted to numbers, and the numbers are then compared directly. NaN values compare equal to each other, and equal to an empty sequence, but less than anything else.

This class is used in XSLT only, so there is no need to handle XQuery's "empty least" vs "empty greatest" options.

Author:

Michael H. Kay

See Also:

Serialized Form

Method Summary

int	compareAtomicValues(AtomicValue a, AtomicValue b) Compare two Items by converting them to numbers and comparing the numeric values.
boolean	comparesEqual(AtomicValue a, AtomicValue b) Compare two AtomicValue objects for equality according to the rules for their data type.
ComparisonKey	getComparisonKey(AtomicValue a) Get a comparison key for an object.
static NumericComparer	getInstance()
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

Method Detail

getInstance

public static NumericComparer getInstance()

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)

Compare two Items by converting them to numbers and comparing the numeric values. If either value cannot be converted to a number, it is treated as NaN, and compares less that the other (two NaN values compare equal).

Specified by:

compareAtomicValues in interface AtomicComparer

Parameters:

a - the first Item to be compared.

b - the second Item to be compared.

Returns:

<0 if a0 if a>b

Throws:

ClassCastException - if the objects are not Items

comparesEqual

public boolean comparesEqual(AtomicValue a,
                             AtomicValue b)

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

getComparisonKey

public ComparisonKey getComparisonKey(AtomicValue a)

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