| /* |
| * Copyright (c) 1997, 2007, 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 |
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| * 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 |
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| */ |
| |
| 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 <i>natural |
| * ordering</i>, and the class's <tt>compareTo</tt> method is referred to as |
| * its <i>natural comparison method</i>.<p> |
| * |
| * 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}.<p> |
| * |
| * The natural ordering for a class <tt>C</tt> is said to be <i>consistent |
| * with equals</i> if and only if <tt>e1.compareTo(e2) == 0</tt> has |
| * the same boolean value as <tt>e1.equals(e2)</tt> for every |
| * <tt>e1</tt> and <tt>e2</tt> of class <tt>C</tt>. Note that <tt>null</tt> |
| * is not an instance of any class, and <tt>e.compareTo(null)</tt> should |
| * throw a <tt>NullPointerException</tt> even though <tt>e.equals(null)</tt> |
| * returns <tt>false</tt>.<p> |
| * |
| * 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 <tt>equals</tt> |
| * method.<p> |
| * |
| * For example, if one adds two keys <tt>a</tt> and <tt>b</tt> such that |
| * <tt>(!a.equals(b) && a.compareTo(b) == 0)</tt> to a sorted |
| * set that does not use an explicit comparator, the second <tt>add</tt> |
| * operation returns false (and the size of the sorted set does not increase) |
| * because <tt>a</tt> and <tt>b</tt> are equivalent from the sorted set's |
| * perspective.<p> |
| * |
| * Virtually all Java core classes that implement <tt>Comparable</tt> have natural |
| * orderings that are consistent with equals. One exception is |
| * <tt>java.math.BigDecimal</tt>, whose natural ordering equates |
| * <tt>BigDecimal</tt> objects with equal values and different precisions |
| * (such as 4.0 and 4.00).<p> |
| * |
| * For the mathematically inclined, the <i>relation</i> that defines |
| * the natural ordering on a given class C is:<pre> |
| * {(x, y) such that x.compareTo(y) <= 0}. |
| * </pre> The <i>quotient</i> for this total order is: <pre> |
| * {(x, y) such that x.compareTo(y) == 0}. |
| * </pre> |
| * |
| * It follows immediately from the contract for <tt>compareTo</tt> that the |
| * quotient is an <i>equivalence relation</i> on <tt>C</tt>, and that the |
| * natural ordering is a <i>total order</i> on <tt>C</tt>. When we say that a |
| * class's natural ordering is <i>consistent with equals</i>, 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:<pre> |
| * {(x, y) such that x.equals(y)}. </pre><p> |
| * |
| * This interface is a member of the |
| * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * @param <T> the type of objects that this object may be compared to |
| * |
| * @author Josh Bloch |
| * @see java.util.Comparator |
| * @since 1.2 |
| */ |
| |
| public interface Comparable<T> { |
| /** |
| * 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. |
| * |
| * <p>The implementor must ensure <tt>sgn(x.compareTo(y)) == |
| * -sgn(y.compareTo(x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This |
| * implies that <tt>x.compareTo(y)</tt> must throw an exception iff |
| * <tt>y.compareTo(x)</tt> throws an exception.) |
| * |
| * <p>The implementor must also ensure that the relation is transitive: |
| * <tt>(x.compareTo(y)>0 && y.compareTo(z)>0)</tt> implies |
| * <tt>x.compareTo(z)>0</tt>. |
| * |
| * <p>Finally, the implementor must ensure that <tt>x.compareTo(y)==0</tt> |
| * implies that <tt>sgn(x.compareTo(z)) == sgn(y.compareTo(z))</tt>, for |
| * all <tt>z</tt>. |
| * |
| * <p>It is strongly recommended, but <i>not</i> strictly required that |
| * <tt>(x.compareTo(y)==0) == (x.equals(y))</tt>. Generally speaking, any |
| * class that implements the <tt>Comparable</tt> 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." |
| * |
| * <p>In the foregoing description, the notation |
| * <tt>sgn(</tt><i>expression</i><tt>)</tt> designates the mathematical |
| * <i>signum</i> function, which is defined to return one of <tt>-1</tt>, |
| * <tt>0</tt>, or <tt>1</tt> according to whether the value of |
| * <i>expression</i> 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); |
| } |
