net.sf.saxon.expr.sort
Class GenericAtomicComparer

java.lang.Object
  net.sf.saxon.expr.sort.GenericAtomicComparer

All Implemented Interfaces:

Serializable, AtomicComparer

public class GenericAtomicComparer
extends 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

See Also:

Serialized Form

Constructor Summary

GenericAtomicComparer(StringCollator collator, XPathContext conversionContext)
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.
StringCollator	getCollator() Get the collation used by this AtomicComparer if any
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

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GenericAtomicComparer

public GenericAtomicComparer(StringCollator collator,
                             XPathContext conversionContext)

Create an GenericAtomicComparer

Parameters:

collator - the collation to be used

conversionContext - a context, used when converting untyped atomic values to the target type.

Method Detail

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

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

getStringCollator

public StringCollator getStringCollator()

Get the underlying string collator

Returns:

the string collator

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 < b, 0 if a = b, >0 if a > b

Throws:

ClassCastException - if the objects are not comparable

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

Throws:

ClassCastException - if the objects are not comparable

NoDynamicContextException

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