java.util
Interface Comparator<T>
public
interface
Comparator<T>
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.
Since: 1.2
See Also: Comparable TreeMap TreeSet SortedMap SortedSet (Object[], Comparator) Serializable
UNKNOWN: updated to 1.4
| Method Summary |
|---|
| int | compare(T o1, T 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. |
public int compare(
T o1,
T 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. 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 o2 the second object
Returns: the comparison
Throws: ClassCastException if the elements are not of types that can be
compared by this ordering.
public boolean equals(
Object obj)
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
Returns: true if it is a Comparator that imposes the same order
See Also: equals