Java Reference
In-Depth Information
the objects belong to classes that implement the
Comparable
interface. That
interface has a single method:
public interface Comparable
{
int compareTo(Object otherObject);
}
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The call
a.compareTo(b)
must return a negative number if
a
should come before
b
, 0 if
a
and
b
are the same,
and a positive number otherwise.
Several classes in the standard Java library, such as the
String
and
Date
classes,
implement the
Comparable
interface.
You can implement the
Comparable
interface for your own classes as well. For
example, to sort a collection of coins, the
Coi n
class would need to implement this
interface and define a
compareTo
method:
public class Coin implements Comparable
{
. . .
public int compareTo(Object otherObject)
{
Coin other = (Coin) otherObject;
if (value < other.value) return -1;
if (value == other.value) return 0;
return 1;
}
. . .
}
When you implement the
compareTo
method of the
Comparable
interface, you
must make sure that the method defines a total ordering relationship, with the
following three properties:
ȗ Antisymmetric: If
a.compareTo(b)
ʎ 0, then
b.compareTo(a)
ʏ 0
ȗ Reflexive:
a.compareTo(a)
= 0
