net.sf.saxon.expr.sort
Class AtomicSortComparer

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

All Implemented Interfaces:

Serializable, AtomicComparer

Direct Known Subclasses:

EquivalenceComparer

public class AtomicSortComparer
extends 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

See Also:

Serialized Form

Field Summary

protected static StructuredQName

COLLATION_KEY_NaN

Constructor Summary

protected

AtomicSortComparer(StringCollator collator, int itemType, XPathContext context)

Method Summary

int	compareAtomicValues(AtomicValue a, AtomicValue b) Compare two AtomicValue objects according to the rules for their data type.
protected int	compareNonComparables(AtomicValue a, AtomicValue b) Compare two values that are known to be non-comparable.
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.
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

Methods inherited from class java.lang.Object

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

Field Detail

COLLATION_KEY_NaN

protected static StructuredQName COLLATION_KEY_NaN

Constructor Detail

AtomicSortComparer

protected AtomicSortComparer(StringCollator collator,
                             int itemType,
                             XPathContext context)

Method Detail

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

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 StringCollator

Returns:

the underlying collator

getItemType

public int getItemType()

Get the requested item type

Returns:

the item type

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

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.

compareNonComparables

protected int compareNonComparables(AtomicValue a,
                                    AtomicValue b)

Compare two values that are known to be non-comparable. In the base class this method throws a ClassCastException. In a subclass it is overridden to return Value.INDETERMINATE_ORDERING

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, 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

Throws:

NoDynamicContextException