net.sf.saxon.sort

Class NumericComparer

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

Method Summary
intcompareAtomicValues(AtomicValue a, AtomicValue b)
Compare two Items by converting them to numbers and comparing the numeric values.
booleancomparesEqual(AtomicValue a, AtomicValue b)
Compare two AtomicValue objects for equality according to the rules for their data type.
ComparisonKeygetComparisonKey(AtomicValue a)
Get a comparison key for an object.
static NumericComparergetInstance()
AtomicComparerprovideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison

Method Detail

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).

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.

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.

getInstance

public static NumericComparer getInstance()

provideContext

public AtomicComparer provideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison

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