| java.util.Comparator
| Comparator | | public interface Comparator (Code) | | Interface for objects that specify an ordering between objects. The ordering
should be total, such that any two objects of the correct type
can be compared, and the comparison is reflexive, anti-symmetric, and
transitive. It is also recommended that the comparator be consistent
with equals, although this is not a strict requirement. A relation
is consistent with equals if these two statements always have the same
results (if no exceptions occur):
compare((Object) e1, (Object) e2) == 0 and
e1.equals((Object) e2)
Comparators that violate consistency with equals may cause strange behavior
in sorted lists and sets. For example, a case-sensitive dictionary order
comparison of Strings is consistent with equals, but if it is
case-insensitive it is not, because "abc" and "ABC" compare as equal even
though "abc".equals("ABC") returns false.
In general, Comparators should be Serializable, because when they are passed
to Serializable data structures such as SortedMap or SortedSet, the entire
data structure will only serialize correctly if the comparator is
Serializable.
author:
Original author unknown
author:
Eric Blake
See Also: Comparable
See Also: TreeMap
See Also: TreeSet
See Also: SortedMap
See Also: SortedSet
See Also: Arrays.sort(Object[]Comparator)
See Also: java.io.Serializable
since:
1.2 |
| Method Summary | |
| int | compare(Object o1, Object o2)
Return an integer that is negative, zero or positive depending on whether
the first argument is less than, equal to or greater than the second
according to this ordering. | | boolean | equals(Object obj)
Return true if the object is equal to this object. |
| compare | | int compare(Object o1, Object o2)(Code) | | Return an integer that is negative, zero or positive depending on whether
the first argument is less than, equal to or greater than the second
according to this ordering. This method should obey the following
contract:
- if compare(a, b) < 0 then compare(b, a) > 0
- if compare(a, b) throws an exception, so does compare(b, a)
- if compare(a, b) < 0 and compare(b, c) < 0 then compare(a, c)
< 0
- if compare(a, b) == 0 then compare(a, c) and compare(b, c) must
have the same sign
To be consistent with equals, the following additional constraint is
in place:
- if a.equals(b) or both a and b are null, then
compare(a, b) == 0.
Although it is permissible for a comparator to provide an order
inconsistent with equals, that should be documented.
Parameters:
o1 - the first object
Parameters:
o2 - the second object the comparison
throws:
ClassCastException - if the elements are not of types that can becompared by this ordering. |
| equals | | boolean equals(Object obj)(Code) | | Return true if the object is equal to this object. To be
considered equal, the argument object must satisfy the constraints
of Object.equals(), be a Comparator, and impose the
same ordering as this Comparator. The default implementation
inherited from Object is usually adequate.
Parameters:
obj - The object true if it is a Comparator that imposes the same order
See Also: Object.equals(Object) |
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