net.sf.saxon.expr.sort
Class DoubleSortComparer

java.lang.Object
  extended by net.sf.saxon.expr.sort.DoubleSortComparer
All Implemented Interfaces:
Serializable, AtomicComparer

public class DoubleSortComparer
extends Object
implements AtomicComparer

An AtomicComparer used for sorting values that are known to be numeric. It also supports a separate method for getting a collation key to test equality of items. This comparator treats NaN values as equal to each other, and less than any other value.

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)
          Test whether two values compare equal.
 StringCollator getCollator()
          Get the collation used by this AtomicComparer if any
 ComparisonKey getComparisonKey(AtomicValue a)
          Get a comparison key for an object.
static DoubleSortComparer 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 DoubleSortComparer getInstance()
Get the singular instance of this class

Returns:
the singular 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.

Specified by:
compareAtomicValues in interface AtomicComparer
Parameters:
a - the first object to be compared. It is intended that this should normally 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 java.util.Comparable interface.
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:
<0 if a0 if a>b
Throws:
ClassCastException - if the objects are not comparable

comparesEqual

public boolean comparesEqual(AtomicValue a,
                             AtomicValue b)
Test whether two values compare equal. Note that for this comparer, NaN is considered equal to itself

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

getComparisonKey

public ComparisonKey getComparisonKey(AtomicValue a)
Get a comparison key for an object. This must satisfy the rule that if two objects are equal as defined by the XPath eq operator, then their comparison keys are equal as defined by 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


Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.