## net.sf.saxon.expr.sort
Interface AtomicComparer

All Superinterfaces:
  Serializable

All Known Implementing Classes:
  AtomicSortComparer, CalendarValueComparer, CodepointCollatingComparer, CollatingAtomicComparer, ComparableAtomicValueComparer, DecimalSortComparer, DescendingComparer, DoubleSortComparer, EmptyGreatestComparer, EqualityComparer, EquivalenceComparer, GenericAtomicComparer, NumericComparer, NumericComparer11, TextComparer

    public interface AtomicComparer

extends Serializable

Interface representing an object that can be used to compare two XPath atomic values for equality or for ordering.

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.
`AtomicComparer` `provideContext(XPathContext context)` Supply the dynamic context in case this is needed for the comparison

Method Detail

### getCollator

    StringCollator getCollator()

  Get the collation used by this AtomicComparer if any

  Returns:
    the collation used for comparing strings, or null if not applicable

### provideContext

    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

### compareAtomicValues

    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.

  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

    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.

  Parameters:
    `a` - the first object to be compared.
    `b` - the second object to be compared.
  Returns:
    true if the values are equal, false if not
  Throws:
    `ClassCastException` - if the objects are not comparable
    `NoDynamicContextException`

### getComparisonKey

    ComparisonKey getComparisonKey(AtomicValue a)
                                   throws NoDynamicContextException

  Get a comparison key for an object. This must satisfy the rule that if two objects are equal according to the XPath eq operator, then their comparison keys are equal according to the Java equals() method, and vice versa. There is no requirement that the comparison keys should reflect the ordering of the underlying objects.

  Throws:
    `NoDynamicContextException`

Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.