net.sf.saxon.sort

Class GenericAtomicComparer

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

Constructor Summary
GenericAtomicComparer(StringCollator collator, XPathContext conversionContext)
Create an GenericAtomicComparer
Method Summary
intcompareAtomicValues(AtomicValue a, AtomicValue b)
Compare two AtomicValue objects according to the rules for their data type.
booleancomparesEqual(AtomicValue a, AtomicValue b)
Compare two AtomicValue objects for equality according to the rules for their data type.
ComparisonKeygetComparisonKey(AtomicValue a)
Get a comparison key for an object.
StringCollatorgetStringCollator()
Get the underlying string collator
static AtomicComparermakeAtomicComparer(BuiltInAtomicType type0, BuiltInAtomicType type1, StringCollator collator, XPathContext context)
Factory method to make a GenericAtomicComparer for values of known types
AtomicComparerprovideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison

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

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.

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)
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.

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

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.

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

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