net.sf.saxon.sort

Class AtomicSortComparer

Implemented Interfaces:
AtomicComparer, Serializable

public class AtomicSortComparer
extends java.lang.Object
implements AtomicComparer

An AtomicComparer used for comparing atomic values of arbitrary item types. It encapsulates a collator that is used when the values to be compared are strings. It also supports a separate method for testing equality of items, which can be used for data types that are not ordered. The AtomicSortComparer is identical to the GenericAtomicComparer except for its handling of NaN: it treats NaN values as lower than any other value, and as equal to each other.
Author:
Michael H. Kay

Field Summary

protected static StructuredQName
COLLATION_KEY_NaN

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.
ComparisonKey
getComparisonKey(AtomicValue a)
Get a comparison key for an object.
int
getItemType()
Get the requested item type
StringCollator
getStringCollator()
Get the underlying StringCollator
static AtomicComparer
makeSortComparer(StringCollator collator, int itemType, XPathContext context)
Factory method to get an atomic comparer suitable for sorting or for grouping (operations in which NaN is considered equal to NaN)
AtomicComparer
provideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison

Field Details

COLLATION_KEY_NaN

protected static StructuredQName COLLATION_KEY_NaN

Method Details

compareAtomicValues

public int compareAtomicValues(AtomicValue a,
                               AtomicValue b)
            throws NoDynamicContextException
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 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

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

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, 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

getItemType

public int getItemType()
Get the requested item type
Returns:
the item type

getStringCollator

public StringCollator getStringCollator()
Get the underlying StringCollator
Returns:
the underlying collator

makeSortComparer

public static AtomicComparer makeSortComparer(StringCollator collator,
                                              int itemType,
                                              XPathContext context)
Factory method to get an atomic comparer suitable for sorting or for grouping (operations in which NaN is considered equal to NaN)
Parameters:
collator - Collating comparer to be used when comparing strings. This argument may be null if the itemType excludes the possibility of comparing strings. If the method is called at compile time, this should be a NamedCollation so that it can be cloned at run-time.
itemType - the primitive item type of the values to be compared
context - Dynamic context (may be an EarlyEvaluationContext)
Returns:
a suitable AtomicComparer

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