author | rriggs |
Sat, 01 Mar 2014 11:57:57 -0500 | |
changeset 23040 | 0cb50d5761df |
parent 21307 | d9d1ad598db1 |
permissions | -rw-r--r-- |
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/* |
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8005623: Retrofit FunctionalInterface annotations to core platform interfaces
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* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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package java.lang; |
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import java.util.*; |
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/** |
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* This interface imposes a total ordering on the objects of each class that |
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* implements it. This ordering is referred to as the class's <i>natural |
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* ordering</i>, and the class's <tt>compareTo</tt> method is referred to as |
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* its <i>natural comparison method</i>.<p> |
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* |
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* Lists (and arrays) of objects that implement this interface can be sorted |
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* automatically by {@link Collections#sort(List) Collections.sort} (and |
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* {@link Arrays#sort(Object[]) Arrays.sort}). Objects that implement this |
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* interface can be used as keys in a {@linkplain SortedMap sorted map} or as |
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* elements in a {@linkplain SortedSet sorted set}, without the need to |
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* specify a {@linkplain Comparator comparator}.<p> |
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* |
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* The natural ordering for a class <tt>C</tt> is said to be <i>consistent |
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* with equals</i> if and only if <tt>e1.compareTo(e2) == 0</tt> has |
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* the same boolean value as <tt>e1.equals(e2)</tt> for every |
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* <tt>e1</tt> and <tt>e2</tt> of class <tt>C</tt>. Note that <tt>null</tt> |
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* is not an instance of any class, and <tt>e.compareTo(null)</tt> should |
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* throw a <tt>NullPointerException</tt> even though <tt>e.equals(null)</tt> |
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* returns <tt>false</tt>.<p> |
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* |
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* It is strongly recommended (though not required) that natural orderings be |
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* consistent with equals. This is so because sorted sets (and sorted maps) |
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* without explicit comparators behave "strangely" when they are used with |
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* elements (or keys) whose natural ordering is inconsistent with equals. In |
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* particular, such a sorted set (or sorted map) violates the general contract |
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* for set (or map), which is defined in terms of the <tt>equals</tt> |
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* method.<p> |
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* |
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* For example, if one adds two keys <tt>a</tt> and <tt>b</tt> such that |
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* {@code (!a.equals(b) && a.compareTo(b) == 0)} to a sorted |
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* set that does not use an explicit comparator, the second <tt>add</tt> |
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* operation returns false (and the size of the sorted set does not increase) |
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* because <tt>a</tt> and <tt>b</tt> are equivalent from the sorted set's |
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* perspective.<p> |
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* |
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* Virtually all Java core classes that implement <tt>Comparable</tt> have natural |
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* orderings that are consistent with equals. One exception is |
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* <tt>java.math.BigDecimal</tt>, whose natural ordering equates |
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* <tt>BigDecimal</tt> objects with equal values and different precisions |
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* (such as 4.0 and 4.00).<p> |
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* |
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* For the mathematically inclined, the <i>relation</i> that defines |
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* the natural ordering on a given class C is:<pre> |
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* {(x, y) such that x.compareTo(y) <= 0}. |
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* </pre> The <i>quotient</i> for this total order is: <pre> |
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* {(x, y) such that x.compareTo(y) == 0}. |
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* </pre> |
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* |
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* It follows immediately from the contract for <tt>compareTo</tt> that the |
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* quotient is an <i>equivalence relation</i> on <tt>C</tt>, and that the |
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* natural ordering is a <i>total order</i> on <tt>C</tt>. When we say that a |
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* class's natural ordering is <i>consistent with equals</i>, we mean that the |
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* quotient for the natural ordering is the equivalence relation defined by |
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* the class's {@link Object#equals(Object) equals(Object)} method:<pre> |
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* {(x, y) such that x.equals(y)}. </pre><p> |
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* |
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* This interface is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @param <T> the type of objects that this object may be compared to |
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* |
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* @author Josh Bloch |
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* @see java.util.Comparator |
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* @since 1.2 |
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*/ |
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public interface Comparable<T> { |
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/** |
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* Compares this object with the specified object for order. Returns a |
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* negative integer, zero, or a positive integer as this object is less |
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* than, equal to, or greater than the specified object. |
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* |
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* <p>The implementor must ensure <tt>sgn(x.compareTo(y)) == |
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* -sgn(y.compareTo(x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This |
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* implies that <tt>x.compareTo(y)</tt> must throw an exception iff |
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* <tt>y.compareTo(x)</tt> throws an exception.) |
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* |
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* <p>The implementor must also ensure that the relation is transitive: |
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* <tt>(x.compareTo(y)>0 && y.compareTo(z)>0)</tt> implies |
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* <tt>x.compareTo(z)>0</tt>. |
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* |
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* <p>Finally, the implementor must ensure that <tt>x.compareTo(y)==0</tt> |
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* implies that <tt>sgn(x.compareTo(z)) == sgn(y.compareTo(z))</tt>, for |
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* all <tt>z</tt>. |
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* |
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* <p>It is strongly recommended, but <i>not</i> strictly required that |
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* <tt>(x.compareTo(y)==0) == (x.equals(y))</tt>. Generally speaking, any |
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* class that implements the <tt>Comparable</tt> interface and violates |
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* this condition should clearly indicate this fact. The recommended |
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* language is "Note: this class has a natural ordering that is |
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* inconsistent with equals." |
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* |
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* <p>In the foregoing description, the notation |
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* <tt>sgn(</tt><i>expression</i><tt>)</tt> designates the mathematical |
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* <i>signum</i> function, which is defined to return one of <tt>-1</tt>, |
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* <tt>0</tt>, or <tt>1</tt> according to whether the value of |
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* <i>expression</i> is negative, zero or positive. |
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* |
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* @param o the object to be compared. |
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* @return a negative integer, zero, or a positive integer as this object |
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* is less than, equal to, or greater than the specified object. |
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* |
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* @throws NullPointerException if the specified object is null |
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* @throws ClassCastException if the specified object's type prevents it |
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* from being compared to this object. |
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*/ |
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public int compareTo(T o); |
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} |