java.lang.Comparable Maven / Gradle / Ivy
Show all versions of android-all Show documentation
/*
* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.lang;
import java.util.*;
/**
* 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 {@link Collections#sort(List) Collections.sort} (and
* {@link Arrays#sort(Object[]) Arrays.sort}). Objects that implement this
* interface can be used as keys in a {@linkplain SortedMap sorted map} or as
* elements in a {@linkplain SortedSet sorted set}, without the need to
* specify a {@linkplain Comparator 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
* {@code (!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 quotient for this total order is:
* {(x, y) such that x.compareTo(y) == 0}.
*
*
* It follows immediately from the contract for compareTo that the
* quotient is an equivalence relation on C, and that the
* natural ordering is a total order on C. When we say that a
* class's natural ordering is consistent with equals, we mean that the
* quotient for the natural ordering is the equivalence relation defined by
* the class's {@link Object#equals(Object) equals(Object)} method:
* {(x, y) such that x.equals(y)}.
*
* This interface is a member of the
*
* Java Collections Framework.
*
* @param the type of objects that this object may be compared to
*
* @author Josh Bloch
* @see java.util.Comparator
* @since 1.2
*/
public interface Comparable {
/**
* Compares this object with the specified object for order. Returns a
* negative integer, zero, or a positive integer as this object is less
* than, equal to, or greater than the specified object.
*
* The implementor must ensure sgn(x.compareTo(y)) ==
* -sgn(y.compareTo(x)) for all x and y. (This
* implies that x.compareTo(y) must throw an exception iff
* y.compareTo(x) throws an exception.)
*
*
The implementor must also ensure that the relation is transitive:
* (x.compareTo(y)>0 && y.compareTo(z)>0) implies
* x.compareTo(z)>0.
*
*
Finally, the implementor must ensure that x.compareTo(y)==0
* implies that sgn(x.compareTo(z)) == sgn(y.compareTo(z)), for
* all z.
*
*
It is strongly recommended, but not strictly required that
* (x.compareTo(y)==0) == (x.equals(y)). Generally speaking, any
* class that implements the Comparable interface and violates
* this condition should clearly indicate this fact. The recommended
* language is "Note: this class has a natural ordering that is
* inconsistent with equals."
*
*
In the foregoing description, the notation
* sgn(expression) designates the mathematical
* signum function, which is defined to return one of -1,
* 0, or 1 according to whether the value of
* expression is negative, zero or positive.
*
* @param o the object to be compared.
* @return a negative integer, zero, or a positive integer as this object
* is less than, equal to, or greater than the specified object.
*
* @throws NullPointerException if the specified object is null
* @throws ClassCastException if the specified object's type prevents it
* from being compared to this object.
*/
public int compareTo(T o);
}