net.sf.saxon.expr.sort
Class AtomicSortComparer

java.lang.Object
  extended by 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
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

public 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 SimpleCollation 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


Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.