org.apache.commons.collections.comparators
Class ComparableComparator

java.lang.Object
  extended by org.apache.commons.collections.comparators.ComparableComparator
All Implemented Interfaces:
Serializable, Comparator<Comparable>

public class ComparableComparator
extends Object
implements Comparator<Comparable>, Serializable

A Comparator that compares Comparable objects.

This Comparator is useful, for example, for enforcing the natural order in custom implementations of SortedSet and SortedMap.

Note: In the 2.0 and 2.1 releases of Commons Collections, this class would throw a ClassCastException if either of the arguments to compare were null, not Comparable, or for which compareTo gave inconsistent results. This is no longer the case. See compare for details.

Since:
Commons Collections 2.0
Version:
$Revision: 1.1.1.1 $ $Date: 2005/05/23 04:34:07 $
Author:
Matt Hall, John Watkinson, Henri Yandell
See Also:
Collections.reverseOrder(), Serialized Form

Constructor Summary
ComparableComparator()
          Constructor whose use should be avoided.
 
Method Summary
 int compare(Comparable obj1, Comparable obj2)
          Compare the two Comparable arguments.
 boolean equals(Object object)
          Returns true iff that Object is is a Comparator whose ordering is known to be equivalent to mine.
static ComparableComparator getInstance()
          Gets the singleton instance of a ComparableComparator.
 int hashCode()
          Implement a hash code for this comparator that is consistent with equals.
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

ComparableComparator

public ComparableComparator()
Constructor whose use should be avoided.

Please use the getInstance() method whenever possible.

Method Detail

getInstance

public static ComparableComparator getInstance()
Gets the singleton instance of a ComparableComparator.

Developers are encouraged to use the comparator returned from this method instead of constructing a new instance to reduce allocation and GC overhead when multiple comparable comparators may be used in the same VM.

Returns:
the singleton ComparableComparator

compare

public int compare(Comparable obj1,
                   Comparable obj2)
Compare the two Comparable arguments. This method is equivalent to:
((Comparable)obj1).compareTo(obj2)

Specified by:
compare in interface Comparator<Comparable>
Parameters:
obj1 - the first object to compare
obj2 - the second object to compare
Returns:
negative if obj1 is less, positive if greater, zero if equal
Throws:
NullPointerException - when obj1 is null, or when ((Comparable)obj1).compareTo(obj2) does
ClassCastException - when obj1 is not a Comparable, or when ((Comparable)obj1).compareTo(obj2) does

hashCode

public int hashCode()
Implement a hash code for this comparator that is consistent with equals.

Overrides:
hashCode in class Object
Returns:
a hash code for this comparator.
Since:
Commons Collections 3.0

equals

public boolean equals(Object object)
Returns true iff that Object is is a Comparator whose ordering is known to be equivalent to mine.

This implementation returns true iff object.getClass() equals this.getClass(). Subclasses may want to override this behavior to remain consistent with the Comparator.equals(Object) contract.

Specified by:
equals in interface Comparator<Comparable>
Overrides:
equals in class Object
Parameters:
object - the object to compare with
Returns:
true if equal
Since:
Commons Collections 3.0


Copyright © 2005-2005 Apache Software Foundation, Matt Hall, John Watkinson. All Rights Reserved.