public abstract interface Comparable <T>

This interface imposes a total ordering on the objects of each class that
implements it. This ordering is referred to as the class's *natural
ordering*, and the class's ` compareTo`

method is referred to as
its *natural comparison method*.

Lists (and arrays) of objects that implement this interface can be sorted
automatically by `Collections.sort`

(and
`Arrays.sort`

). Objects that implement this
interface can be used as keys in a sorted map or as
elements in a sorted set, without the need to
specify a comparator.

The natural ordering for a class ` C`

is said to be *consistent
with equals* if and only if ` e1.compareTo(e2) == 0`

has
the same boolean value as ` e1.equals(e2)`

for every
` e1`

and ` e2`

of class ` C`

. Note that ` null`

is not an instance of any class, and ` e.compareTo(null)`

should
throw a ` NullPointerException`

even though ` e.equals(null)`

returns ` false`

.

It is strongly recommended (though not required) that natural orderings be
consistent with equals. This is so because sorted sets (and sorted maps)
without explicit comparators behave "strangely" when they are used with
elements (or keys) whose natural ordering is inconsistent with equals. In
particular, such a sorted set (or sorted map) violates the general contract
for set (or map), which is defined in terms of the ` equals`

method.

For example, if one adds two keys ` a`

and ` b`

such that
` (!a.equals(b) && a.compareTo(b) == 0)`

to a sorted
set that does not use an explicit comparator, the second ` add`

operation returns false (and the size of the sorted set does not increase)
because ` a`

and ` b`

are equivalent from the sorted set's
perspective.

Virtually all Java core classes that implement ` Comparable`

have natural
orderings that are consistent with equals. One exception is
` java.math.BigDecimal`

, whose natural ordering equates
` BigDecimal`

objects with equal values and different precisions
(such as 4.0 and 4.00).

For the mathematically inclined, the *relation* that defines
the natural ordering on a given class C is:

```
{(x, y) such that x.compareTo(y) <= 0
```

.
}

The ```
{(x, y) such that x.compareTo(y) == 0
```

.
}

It follows immediately from the contract for ` compareTo`

that the
quotient is an ` C`

, and that the
natural ordering is a ` C`

. When we say that a
class's natural ordering is `equals(Object)`

method:{(x, y) such that x.equals(y)}.

This interface is a member of the Java Collections Framework.

`<T>` | the type of objects that this object may be compared to |

java.util.Comparator