Comparators.java revision f121f31fd91c5a557225cd6a97418e716529eb2d 
1/*
2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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25package java.util;
26
27import java.io.Serializable;
28import java.util.function.BinaryOperator;
29import java.util.function.Function;
30import java.util.function.ToDoubleFunction;
31import java.util.function.ToIntFunction;
32import java.util.function.ToLongFunction;
33
34/**
35 * Package private supporting class for {@link Comparator}.
36 */
37class Comparators {
38    private Comparators() {
39        throw new AssertionError("no instances");
40    }
41
42    /**
43     * Compares {@link Comparable} objects in natural order.
44     *
45     * @see Comparable
46     */
47    enum NaturalOrderComparator implements Comparator<Comparable<Object>> {
48        INSTANCE;
49
50        @Override
51        public int compare(Comparable<Object> c1, Comparable<Object> c2) {
52            return c1.compareTo(c2);
53        }
54
55        @Override
56        public Comparator<Comparable<Object>> reversed() {
57            return Comparator.reverseOrder();
58        }
59    }
60
61    /**
62     * Null-friendly comparators
63     */
64    final static class NullComparator<T> implements Comparator<T>, Serializable {
65        private static final long serialVersionUID = -7569533591570686392L;
66        private final boolean nullFirst;
67        // if null, non-null Ts are considered equal
68        private final Comparator<T> real;
69
70        @SuppressWarnings("unchecked")
71        NullComparator(boolean nullFirst, Comparator<? super T> real) {
72            this.nullFirst = nullFirst;
73            this.real = (Comparator<T>) real;
74        }
75
76        @Override
77        public int compare(T a, T b) {
78            if (a == null) {
79                return (b == null) ? 0 : (nullFirst ? -1 : 1);
80            } else if (b == null) {
81                return nullFirst ? 1: -1;
82            } else {
83                return (real == null) ? 0 : real.compare(a, b);
84            }
85        }
86
87        @Override
88        public Comparator<T> thenComparing(Comparator<? super T> other) {
89            Objects.requireNonNull(other);
90            return new NullComparator<>(nullFirst, real == null ? other : real.thenComparing(other));
91        }
92
93        @Override
94        public Comparator<T> reversed() {
95            return new NullComparator<>(!nullFirst, real == null ? null : real.reversed());
96        }
97    }
98}
99