net.sf.saxon.expr.sort
Class DescendingComparer

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

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.

See Also:
Serialized Form

Constructor Summary
DescendingComparer(AtomicComparer base)
           
 
Method Summary
 int compareAtomicValues(AtomicValue a, AtomicValue b)
          Compare two objects.
 boolean comparesEqual(AtomicValue a, AtomicValue b)
          Compare two AtomicValue objects for equality according to the rules for their data type.
 AtomicComparer getBaseComparer()
          Get the underlying (ascending) comparer
 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

DescendingComparer

public DescendingComparer(AtomicComparer base)
Method Detail

getBaseComparer

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

Returns:
the underlying (ascending) comparer

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

compareAtomicValues

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

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 of the wrong type for this Comparer
NoDynamicContextException - if this comparer required access to dynamic context information, notably the implicit timezone, and this information is not available. In general this happens if a context-dependent comparison is attempted at compile-time, and it signals the compiler to generate code that tries again at run-time.

comparesEqual

public boolean comparesEqual(AtomicValue a,
                             AtomicValue b)
                      throws NoDynamicContextException
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:
true if the values are equal, false if not
Throws:
ClassCastException - if the objects are not comparable
NoDynamicContextException

getComparisonKey

public ComparisonKey getComparisonKey(AtomicValue a)
                               throws NoDynamicContextException
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.

Specified by:
getComparisonKey in interface AtomicComparer
Throws:
NoDynamicContextException


Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.