net.sf.saxon.sort

Class GenericAtomicComparer

Implemented Interfaces:
AtomicComparer, Serializable

public class GenericAtomicComparer
extends java.lang.Object
implements AtomicComparer, Serializable

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.
Author:
Michael H. Kay

Constructor Summary

GenericAtomicComparer(StringCollator collator, XPathContext conversion)
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.
ComparisonKey
getComparisonKey(AtomicValue a)
Get a comparison key for an object.
StringCollator
getStringCollator()
Get the underlying string collator
static AtomicComparer
makeAtomicComparer(BuiltInAtomicType type0, BuiltInAtomicType type1, StringCollator collator, XPathContext context)
Factory method to make a GenericAtomicComparer for values of known types
AtomicComparer
provideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison

Constructor Details

GenericAtomicComparer

public GenericAtomicComparer(StringCollator collator,
                             XPathContext conversion)
Create an GenericAtomicComparer
Parameters:
collator - the collation to be used
conversion - a context, used when converting untyped atomic values to the target type.

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 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 a <32b, 0 if a = b, >0 if a > b
Throws:
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 as if they were strings; if different semantics are wanted, the conversion must be done by the caller.
Specified by:
comparesEqual in interface AtomicComparer
Parameters:
a - the first object to be compared. 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

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

getStringCollator

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

makeAtomicComparer

public static AtomicComparer makeAtomicComparer(BuiltInAtomicType type0,
                                                BuiltInAtomicType type1,
                                                StringCollator collator,
                                                XPathContext context)
Factory method to make a GenericAtomicComparer for values of known types
Parameters:
type0 - primitive type of the first operand
type1 - primitive type of the second operand
collator - the collation to be used, if any. This is supplied as a NamedCollation object which encapsulated both the collation URI and the collation itself.
context - the dynamic context
Returns:
a GenericAtomicComparer for values of known types

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