package client.net.sf.saxon.ce.expr.sort;
import client.net.sf.saxon.ce.expr.XPathContext;
import client.net.sf.saxon.ce.lib.StringCollator;
import client.net.sf.saxon.ce.om.StandardNames;
import client.net.sf.saxon.ce.value.AtomicValue;
import client.net.sf.saxon.ce.value.StringValue;
/**
* 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.
*
* <p>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.</p>
*
* @author Michael H. Kay
*
*/
public class CodepointCollatingComparer implements AtomicComparer {
private static CodepointCollator collator = CodepointCollator.getInstance();
private static CodepointCollatingComparer THE_INSTANCE = new CodepointCollatingComparer();
/**
* Get the singular instance of this class
* @return the singleton instance
*/
public static CodepointCollatingComparer getInstance() {
return THE_INSTANCE;
}
private CodepointCollatingComparer() {}
public StringCollator getCollator() {
return collator;
}
/**
* Supply the dynamic context in case this is needed for the comparison
*
* @param context the dynamic evaluation context
* @return either the original AtomicComparer, or a new AtomicComparer in which the context
* is known. The original AtomicComparer is not modified
*/
public AtomicComparer provideContext(XPathContext context) {
return this;
}
/**
* 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.
* @param 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.
* @param b the second object to be compared. This must be either be an instance
* of AtomicValue, or null to represent an empty sequence.
* @return <0 if a<b, 0 if a=b, >0 if a>b
* @throws ClassCastException if the objects are not comparable
*/
public int compareAtomicValues(AtomicValue a, AtomicValue b) {
if (a == null) {
return (b == null ? 0 : -1);
} else if (b == null) {
return +1;
}
StringValue as = (StringValue)a;
StringValue bs = (StringValue)b;
if (as.containsSurrogatePairs() || bs.containsSurrogatePairs()) {
return collator.compareCS(as.getStringValueCS(), bs.getStringValueCS());
} else {
// optimize to use UTF-16 binary comparison
return as.getStringValue().compareTo(bs.getStringValue());
}
}
/**
* 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.
* @param a the first object to be compared.
* @param b the second object to be compared.
* @return <0 if a<b, 0 if a=b, >0 if a>b
* @throws ClassCastException if either value is not xs:string or a subtype
*/
public boolean comparesEqual(AtomicValue a, AtomicValue b) {
StringValue as = (StringValue)a;
StringValue bs = (StringValue)b;
return as.codepointEquals(bs);
}
/**
* 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.
*/
public ComparisonKey getComparisonKey(AtomicValue a) {
StringValue as = (StringValue)a;
return new ComparisonKey(StandardNames.XS_STRING, as.getStringValue());
}
}
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is “Incompatible With Secondary Licenses”, as defined by the Mozilla Public License, v. 2.0.