net.sf.saxon.sort

Class DescendingComparer

public class DescendingComparer extends Object implements AtomicComparer, Serializable

A Comparer used for comparing descending keys. This simply returns the inverse of the result delivered by the base comparer.
Constructor Summary
DescendingComparer(AtomicComparer base)
Method Summary
intcompareAtomicValues(AtomicValue a, AtomicValue b)
Compare two objects.
booleancomparesEqual(AtomicValue a, AtomicValue b)
Compare two AtomicValue objects for equality according to the rules for their data type.
AtomicComparergetBaseComparer()
Get the underlying (ascending) comparer
ComparisonKeygetComparisonKey(AtomicValue a)
Get a comparison key for an object.
AtomicComparerprovideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison

Constructor Detail

DescendingComparer

public DescendingComparer(AtomicComparer base)

Method Detail

compareAtomicValues

public int compareAtomicValues(AtomicValue a, AtomicValue b)
Compare two objects.

Returns: <0 if a0 if a>b

Throws: ClassCastException if the objects are of the wrong type for this Comparer

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. It is intended that this should 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 equals() method. 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: true if the values are equal, false if not

Throws: ClassCastException if the objects are not comparable

getBaseComparer

public AtomicComparer getBaseComparer()
Get the underlying (ascending) comparer

Returns: the underlying (ascending) comparer

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.

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

Throws: NoDynamicContextException if the context is an "early evaluation" (compile-time) context