## net.sf.saxon.expr.sort
Class EqualityComparer

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

All Implemented Interfaces:
  Serializable, AtomicComparer

    public class EqualityComparer

extends Object
implements AtomicComparer

A comparer for comparing two atomic values where (a) equals is defined, and is implemented using the Java equals() method, and (b) ordering is not defined, and results in a dynamic error.

See Also:
  Serialized Form

Field Summary
`static EqualityComparer` `THE_INSTANCE`

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.
`static EqualityComparer` `getInstance()` Get the singleton instance of this class
`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

### THE_INSTANCE

    public static EqualityComparer THE_INSTANCE

Method Detail

### getInstance

    public static EqualityComparer getInstance()

  Get the singleton instance of this class

  Returns:
    the singleton instance of this class

### 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

### 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.

  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

### 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 by converting to the type of the other operand.

  Specified by:
    `comparesEqual` in interface `AtomicComparer`
  Parameters:
    `a` - the first object to be compared. This must be an AtomicValue and it must implement equals() with context-free XPath comparison semantics
    `b` - the second object to be compared. This must be an AtomicValue and it must implement equals() with context-free XPath comparison semantics
  Returns:
    true if the values are equal, false if not
  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.

  Specified by:
    `getComparisonKey` in interface `AtomicComparer`

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