net.sf.saxon.expr.sort
Class CollatingAtomicComparer

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

public class CollatingAtomicComparer
extends Object
implements AtomicComparer

An AtomicComparer used for comparing strings, untypedAtomic values, and URIs using a collation. A CollatingAtomicComparer is used when it is known in advance that both operands will be of these types. 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.

Author:
Michael H. Kay
See Also:
Serialized Form

Constructor Summary
CollatingAtomicComparer(StringCollator collator, Platform platform)
          Create an GenericAtomicComparer
 
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 according to the rules for their data type.
 String getCollationURI()
          Get the collation URI
 StringCollator getCollator()
          Get the collation used by this AtomicComparer if any
 ComparisonKey getComparisonKey(AtomicValue a)
          Get a comparison key for an object.
 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
 

Constructor Detail

CollatingAtomicComparer

public CollatingAtomicComparer(StringCollator collator,
                               Platform platform)
Create an GenericAtomicComparer

Parameters:
collator - the collation to be used. If the method is called at compile time, this should be a NamedCollation so that it can be cloned at run-time.
platform - used to obtain collation keys.
Method Detail

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

getCollationURI

public String getCollationURI()
Get the collation URI

Returns:
the collation URI

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. 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 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)
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.

Specified by:
comparesEqual in interface AtomicComparer
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:
<0 if a0 if a>b
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, then their comparison keys are equal, 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.