net.sf.saxon.expr.sort
Class CodepointCollatingComparer

java.lang.Object
  net.sf.saxon.expr.sort.CodepointCollatingComparer

All Implemented Interfaces:

Serializable, AtomicComparer

public class CodepointCollatingComparer
extends Object
implements AtomicComparer

An AtomicComparer used for comparing strings, untypedAtomic values, and URIs using the Unicode codepoint collation. A CodepointCollatingComparer is used when it is known in advance that both operands will be of these types, and when the collation is the unicode codepoint collation. This enables all conversions and promotions to be bypassed: the string values of both operands are simply extracted and passed to the collator for comparison.

The difference between using this class and using the underlying CodepointCollator directly is that the compare() method in this class expects two instances of AtomicValue as its operands, whereas the underlying class expects two instances of java.lang.String. This class makes use of the extra information held in the wrapping StringValue object, specifically, the knowledge of whether the string contains surrogate pairs.

Author:

Michael H. Kay

See Also:

Serialized Form

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.
StringCollator	getCollator() Get the collation used by this AtomicComparer if any
ComparisonKey	getComparisonKey(AtomicValue a) Get a comparison key for an object.
static CodepointCollatingComparer	getInstance() Get the singular instance of this class
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 CodepointCollatingComparer getInstance()

Get the singular instance of this class

Returns:

the singleton instance

getCollator

public StringCollator getCollator()

Description copied from interface: AtomicComparer

Get the collation used by this AtomicComparer if any

Specified by:

getCollator in interface AtomicComparer

Returns:

the collation used for comparing strings, or null if not applicable

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 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. This must be either be an instance of AtomicValue, or null to represent an empty sequence. Empty collates before non-empty.

b - the second object to be compared. This must be either be an instance of AtomicValue, or null to represent an empty sequence.

Returns:

<0 if a0 if a>b

Throws:

ClassCastException - if the objects are not comparable

comparesEqual

public boolean comparesEqual(AtomicValue a,
                             AtomicValue b)

Compare two AtomicValue objects for equality. The values must be instances of xs:string or a type derived from xs:string. The method will also handle xs:untypedAtomic and xs:anyURI values.

Specified by:

comparesEqual in interface AtomicComparer

Parameters:

a - the first object to be compared.

b - the second object to be compared.

Returns:

<0 if a0 if a>b

Throws:

ClassCastException - if either value is not xs:string or a subtype

getComparisonKey

public ComparisonKey getComparisonKey(AtomicValue a)

Get a comparison key for an object. This must satisfy the rule that if two objects are equal under the XPath eq operator, then their comparison keys are equal under the Java equals() function, 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