1.1 --- a/emul/mini/src/main/java/java/util/Comparator.java Mon Feb 25 19:00:08 2013 +0100
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,168 +0,0 @@
1.4 -/*
1.5 - * Copyright (c) 1997, 2007, Oracle and/or its affiliates. All rights reserved.
1.6 - * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 - *
1.8 - * This code is free software; you can redistribute it and/or modify it
1.9 - * under the terms of the GNU General Public License version 2 only, as
1.10 - * published by the Free Software Foundation. Oracle designates this
1.11 - * particular file as subject to the "Classpath" exception as provided
1.12 - * by Oracle in the LICENSE file that accompanied this code.
1.13 - *
1.14 - * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 - * version 2 for more details (a copy is included in the LICENSE file that
1.18 - * accompanied this code).
1.19 - *
1.20 - * You should have received a copy of the GNU General Public License version
1.21 - * 2 along with this work; if not, write to the Free Software Foundation,
1.22 - * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 - *
1.24 - * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 - * or visit www.oracle.com if you need additional information or have any
1.26 - * questions.
1.27 - */
1.28 -
1.29 -package java.util;
1.30 -
1.31 -/**
1.32 - * A comparison function, which imposes a <i>total ordering</i> on some
1.33 - * collection of objects. Comparators can be passed to a sort method (such
1.34 - * as {@link Collections#sort(List,Comparator) Collections.sort} or {@link
1.35 - * Arrays#sort(Object[],Comparator) Arrays.sort}) to allow precise control
1.36 - * over the sort order. Comparators can also be used to control the order of
1.37 - * certain data structures (such as {@link SortedSet sorted sets} or {@link
1.38 - * SortedMap sorted maps}), or to provide an ordering for collections of
1.39 - * objects that don't have a {@link Comparable natural ordering}.<p>
1.40 - *
1.41 - * The ordering imposed by a comparator <tt>c</tt> on a set of elements
1.42 - * <tt>S</tt> is said to be <i>consistent with equals</i> if and only if
1.43 - * <tt>c.compare(e1, e2)==0</tt> has the same boolean value as
1.44 - * <tt>e1.equals(e2)</tt> for every <tt>e1</tt> and <tt>e2</tt> in
1.45 - * <tt>S</tt>.<p>
1.46 - *
1.47 - * Caution should be exercised when using a comparator capable of imposing an
1.48 - * ordering inconsistent with equals to order a sorted set (or sorted map).
1.49 - * Suppose a sorted set (or sorted map) with an explicit comparator <tt>c</tt>
1.50 - * is used with elements (or keys) drawn from a set <tt>S</tt>. If the
1.51 - * ordering imposed by <tt>c</tt> on <tt>S</tt> is inconsistent with equals,
1.52 - * the sorted set (or sorted map) will behave "strangely." In particular the
1.53 - * sorted set (or sorted map) will violate the general contract for set (or
1.54 - * map), which is defined in terms of <tt>equals</tt>.<p>
1.55 - *
1.56 - * For example, suppose one adds two elements {@code a} and {@code b} such that
1.57 - * {@code (a.equals(b) && c.compare(a, b) != 0)}
1.58 - * to an empty {@code TreeSet} with comparator {@code c}.
1.59 - * The second {@code add} operation will return
1.60 - * true (and the size of the tree set will increase) because {@code a} and
1.61 - * {@code b} are not equivalent from the tree set's perspective, even though
1.62 - * this is contrary to the specification of the
1.63 - * {@link Set#add Set.add} method.<p>
1.64 - *
1.65 - * Note: It is generally a good idea for comparators to also implement
1.66 - * <tt>java.io.Serializable</tt>, as they may be used as ordering methods in
1.67 - * serializable data structures (like {@link TreeSet}, {@link TreeMap}). In
1.68 - * order for the data structure to serialize successfully, the comparator (if
1.69 - * provided) must implement <tt>Serializable</tt>.<p>
1.70 - *
1.71 - * For the mathematically inclined, the <i>relation</i> that defines the
1.72 - * <i>imposed ordering</i> that a given comparator <tt>c</tt> imposes on a
1.73 - * given set of objects <tt>S</tt> is:<pre>
1.74 - * {(x, y) such that c.compare(x, y) <= 0}.
1.75 - * </pre> The <i>quotient</i> for this total order is:<pre>
1.76 - * {(x, y) such that c.compare(x, y) == 0}.
1.77 - * </pre>
1.78 - *
1.79 - * It follows immediately from the contract for <tt>compare</tt> that the
1.80 - * quotient is an <i>equivalence relation</i> on <tt>S</tt>, and that the
1.81 - * imposed ordering is a <i>total order</i> on <tt>S</tt>. When we say that
1.82 - * the ordering imposed by <tt>c</tt> on <tt>S</tt> is <i>consistent with
1.83 - * equals</i>, we mean that the quotient for the ordering is the equivalence
1.84 - * relation defined by the objects' {@link Object#equals(Object)
1.85 - * equals(Object)} method(s):<pre>
1.86 - * {(x, y) such that x.equals(y)}. </pre>
1.87 - *
1.88 - * <p>Unlike {@code Comparable}, a comparator may optionally permit
1.89 - * comparison of null arguments, while maintaining the requirements for
1.90 - * an equivalence relation.
1.91 - *
1.92 - * <p>This interface is a member of the
1.93 - * <a href="{@docRoot}/../technotes/guides/collections/index.html">
1.94 - * Java Collections Framework</a>.
1.95 - *
1.96 - * @param <T> the type of objects that may be compared by this comparator
1.97 - *
1.98 - * @author Josh Bloch
1.99 - * @author Neal Gafter
1.100 - * @see Comparable
1.101 - * @see java.io.Serializable
1.102 - * @since 1.2
1.103 - */
1.104 -
1.105 -public interface Comparator<T> {
1.106 - /**
1.107 - * Compares its two arguments for order. Returns a negative integer,
1.108 - * zero, or a positive integer as the first argument is less than, equal
1.109 - * to, or greater than the second.<p>
1.110 - *
1.111 - * In the foregoing description, the notation
1.112 - * <tt>sgn(</tt><i>expression</i><tt>)</tt> designates the mathematical
1.113 - * <i>signum</i> function, which is defined to return one of <tt>-1</tt>,
1.114 - * <tt>0</tt>, or <tt>1</tt> according to whether the value of
1.115 - * <i>expression</i> is negative, zero or positive.<p>
1.116 - *
1.117 - * The implementor must ensure that <tt>sgn(compare(x, y)) ==
1.118 - * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This
1.119 - * implies that <tt>compare(x, y)</tt> must throw an exception if and only
1.120 - * if <tt>compare(y, x)</tt> throws an exception.)<p>
1.121 - *
1.122 - * The implementor must also ensure that the relation is transitive:
1.123 - * <tt>((compare(x, y)>0) && (compare(y, z)>0))</tt> implies
1.124 - * <tt>compare(x, z)>0</tt>.<p>
1.125 - *
1.126 - * Finally, the implementor must ensure that <tt>compare(x, y)==0</tt>
1.127 - * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
1.128 - * <tt>z</tt>.<p>
1.129 - *
1.130 - * It is generally the case, but <i>not</i> strictly required that
1.131 - * <tt>(compare(x, y)==0) == (x.equals(y))</tt>. Generally speaking,
1.132 - * any comparator that violates this condition should clearly indicate
1.133 - * this fact. The recommended language is "Note: this comparator
1.134 - * imposes orderings that are inconsistent with equals."
1.135 - *
1.136 - * @param o1 the first object to be compared.
1.137 - * @param o2 the second object to be compared.
1.138 - * @return a negative integer, zero, or a positive integer as the
1.139 - * first argument is less than, equal to, or greater than the
1.140 - * second.
1.141 - * @throws NullPointerException if an argument is null and this
1.142 - * comparator does not permit null arguments
1.143 - * @throws ClassCastException if the arguments' types prevent them from
1.144 - * being compared by this comparator.
1.145 - */
1.146 - int compare(T o1, T o2);
1.147 -
1.148 - /**
1.149 - * Indicates whether some other object is "equal to" this
1.150 - * comparator. This method must obey the general contract of
1.151 - * {@link Object#equals(Object)}. Additionally, this method can return
1.152 - * <tt>true</tt> <i>only</i> if the specified object is also a comparator
1.153 - * and it imposes the same ordering as this comparator. Thus,
1.154 - * <code>comp1.equals(comp2)</code> implies that <tt>sgn(comp1.compare(o1,
1.155 - * o2))==sgn(comp2.compare(o1, o2))</tt> for every object reference
1.156 - * <tt>o1</tt> and <tt>o2</tt>.<p>
1.157 - *
1.158 - * Note that it is <i>always</i> safe <i>not</i> to override
1.159 - * <tt>Object.equals(Object)</tt>. However, overriding this method may,
1.160 - * in some cases, improve performance by allowing programs to determine
1.161 - * that two distinct comparators impose the same order.
1.162 - *
1.163 - * @param obj the reference object with which to compare.
1.164 - * @return <code>true</code> only if the specified object is also
1.165 - * a comparator and it imposes the same ordering as this
1.166 - * comparator.
1.167 - * @see Object#equals(Object)
1.168 - * @see Object#hashCode()
1.169 - */
1.170 - boolean equals(Object obj);
1.171 -}